口碑营销成功案例有哪些/搜索引擎优化培训中心

WEB

20) RequestMappingHandlerMapping 与 RequestMappingHandlerAdapter

RequestMappingHandlerMapping 与 RequestMappingHandlerAdapter 俩是一对，分别用来

• 处理 @RequestMapping 映射
• 调用控制器方法、并处理方法参数与方法返回值

演示1 - DispatcherServlet 初始化

代码参考

package com.itheima.a20;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.servlet.HandlerExecutionChain;
import org.springframework.web.servlet.mvc.method.RequestMappingInfo;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Map;public class A20 {private static final Logger log = LoggerFactory.getLogger(A20.class);public static void main(String[] args) throws Exception {AnnotationConfigServletWebServerApplicationContext context =new AnnotationConfigServletWebServerApplicationContext(WebConfig.class);// 作用 解析 @RequestMapping 以及派生注解，生成路径与控制器方法的映射关系, 在初始化时就生成RequestMappingHandlerMapping handlerMapping = context.getBean(RequestMappingHandlerMapping.class);// 获取映射结果Map<RequestMappingInfo, HandlerMethod> handlerMethods = handlerMapping.getHandlerMethods();handlerMethods.forEach((k, v) -> {System.out.println(k + "=" + v);});// 请求来了，获取控制器方法  返回处理器执行链对象MockHttpServletRequest request = new MockHttpServletRequest("GET", "/test4");request.setParameter("name", "张三");request.addHeader("token", "某个令牌");MockHttpServletResponse response = new MockHttpServletResponse();HandlerExecutionChain chain = handlerMapping.getHandler(request);System.out.println(chain);System.out.println(">>>>>>>>>>>>>>>>>>>>>");// HandlerAdapter 作用: 调用控制器方法MyRequestMappingHandlerAdapter handlerAdapter = context.getBean(MyRequestMappingHandlerAdapter.class);handlerAdapter.invokeHandlerMethod(request, response, (HandlerMethod) chain.getHandler());// 检查响应byte[] content = response.getContentAsByteArray();System.out.println(new String(content, StandardCharsets.UTF_8));/*System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有参数解析器");for (HandlerMethodArgumentResolver resolver : handlerAdapter.getArgumentResolvers()) {System.out.println(resolver);}System.out.println(">>>>>>>>>>>>>>>>>>>>> 所有返回值解析器");for (HandlerMethodReturnValueHandler handler : handlerAdapter.getReturnValueHandlers()) {System.out.println(handler);}*//*学到了什么a. DispatcherServlet 是在第一次被访问时执行初始化, 也可以通过配置修改为 Tomcat 启动后就初始化b. 在初始化时会从 Spring 容器中找一些 Web 需要的组件, 如 HandlerMapping、HandlerAdapter 等本章介绍两个最为重要的组件a. RequestMappingHandlerAdapter, 以 @RequestMapping 作为映射路径b. RequestMappingHandlerAdapter, 调用 handlerc. 控制器的具体方法会被当作 handler- handler 的参数和返回值多种多样- 需要解析方法参数, 由 HandlerMethodArgumentResolver 来做- 需要处理方法返回值, 由 HandlerMethodReturnValueHandler 来做*/}
}

package com.itheima.a20;import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.boot.autoconfigure.web.ServerProperties;
import org.springframework.boot.autoconfigure.web.servlet.DispatcherServletRegistrationBean;
import org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.DispatcherServlet;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping;
import org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.List;@Configuration
@ComponentScan
@PropertySource("classpath:application.properties")
@EnableConfigurationProperties({WebMvcProperties.class, ServerProperties.class})
public class WebConfig {// ⬅️内嵌 web 容器工厂@Beanpublic TomcatServletWebServerFactory tomcatServletWebServerFactory(ServerProperties serverProperties) {return new TomcatServletWebServerFactory(serverProperties.getPort());}// ⬅️创建 DispatcherServlet@Beanpublic DispatcherServlet dispatcherServlet() {return new DispatcherServlet();}// ⬅️注册 DispatcherServlet, Spring MVC 的入口@Beanpublic DispatcherServletRegistrationBean dispatcherServletRegistrationBean(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties) {DispatcherServletRegistrationBean registrationBean = new DispatcherServletRegistrationBean(dispatcherServlet, "/");registrationBean.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());return registrationBean;}// 如果用 DispatcherServlet 初始化时默认添加的组件, 并不会作为 bean, 给测试带来困扰// ⬅️1. 加入RequestMappingHandlerMapping@Beanpublic RequestMappingHandlerMapping requestMappingHandlerMapping() {return new RequestMappingHandlerMapping();}// ⬅️2. 继续加入RequestMappingHandlerAdapter, 会替换掉 DispatcherServlet 默认的 4 个 HandlerAdapter@Beanpublic MyRequestMappingHandlerAdapter requestMappingHandlerAdapter() {TokenArgumentResolver tokenArgumentResolver = new TokenArgumentResolver();YmlReturnValueHandler ymlReturnValueHandler = new YmlReturnValueHandler();MyRequestMappingHandlerAdapter handlerAdapter = new MyRequestMappingHandlerAdapter();handlerAdapter.setCustomArgumentResolvers(List.of(tokenArgumentResolver));handlerAdapter.setCustomReturnValueHandlers(List.of(ymlReturnValueHandler));return handlerAdapter;}public HttpMessageConverters httpMessageConverters() {return new HttpMessageConverters();}// ⬅️3. 演示 RequestMappingHandlerAdapter 初始化后, 有哪些参数、返回值处理器// ⬅️3.1 创建自定义参数处理器// ⬅️3.2 创建自定义返回值处理器}

收获💡

1. DispatcherServlet 是在第一次被访问时执行初始化, 也可以通过配置修改为 Tomcat 启动后就初始化
2. 在初始化时会从 Spring 容器中找一些 Web 需要的组件, 如 HandlerMapping、HandlerAdapter 等，并逐一调用它们的初始化
3. RequestMappingHandlerMapping 初始化时，会收集所有 @RequestMapping 映射信息，封装为 Map，其中
   • key 是 RequestMappingInfo 类型，包括请求路径、请求方法等信息
   • value 是 HandlerMethod 类型，包括控制器方法对象、控制器对象
   • 有了这个 Map，就可以在请求到达时，快速完成映射，找到 HandlerMethod 并与匹配的拦截器一起返回给 DispatcherServlet
4. RequestMappingHandlerAdapter 初始化时，会准备 HandlerMethod 调用时需要的各个组件，如：
   • HandlerMethodArgumentResolver 解析控制器方法参数
   • HandlerMethodReturnValueHandler 处理控制器方法返回值

演示2 - 自定义参数与返回值处理器

代码参考

package com.itheima.a20;import org.springframework.core.MethodParameter;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;public class TokenArgumentResolver implements HandlerMethodArgumentResolver {@Override// 是否支持某个参数public boolean supportsParameter(MethodParameter parameter) {Token token = parameter.getParameterAnnotation(Token.class);return token != null;}@Override// 解析参数public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {return webRequest.getHeader("token");}
}

package com.itheima.a20;import org.springframework.core.MethodParameter;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.yaml.snakeyaml.Yaml;import javax.servlet.http.HttpServletResponse;public class YmlReturnValueHandler implements HandlerMethodReturnValueHandler {@Overridepublic boolean supportsReturnType(MethodParameter returnType) {Yml yml = returnType.getMethodAnnotation(Yml.class);return yml != null;}@Override                   //  返回值public void handleReturnValue(Object returnValue, MethodParameter returnType,ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {// 1. 转换返回结果为 yaml 字符串String str = new Yaml().dump(returnValue);// 2. 将 yaml 字符串写入响应HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);response.setContentType("text/plain;charset=utf-8");response.getWriter().print(str);// 3. 设置请求已经处理完毕mavContainer.setRequestHandled(true);}
}

收获💡

1. 体会参数解析器的作用
2. 体会返回值处理器的作用

21) 参数解析器

演示 - 常见参数解析器

代码参考

package com.itheima.a21;import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.core.DefaultParameterNameDiscoverer;
import org.springframework.core.MethodParameter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockPart;
import org.springframework.util.AntPathMatcher;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.annotation.ExpressionValueMethodArgumentResolver;
import org.springframework.web.method.annotation.RequestHeaderMethodArgumentResolver;
import org.springframework.web.method.annotation.RequestParamMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodArgumentResolverComposite;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.multipart.support.StandardServletMultipartResolver;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.servlet.mvc.method.annotation.*;import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;/*目标: 解析控制器方法的参数值常见的参数处理器如下:org.springfr[e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail]@62dd[e-mail][e-mail][e-mail][e-mail][e-mail][e-mail]hodProcessor@35f8a9d3*/
public class A21 {public static void main(String[] args) throws Exception {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(WebConfig.class);DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();// 准备测试 RequestHttpServletRequest request = mockRequest();// 要点1. 控制器方法被封装为 HandlerMethodHandlerMethod handlerMethod = new HandlerMethod(new Controller(), Controller.class.getMethod("test", String.class, String.class, int.class, String.class, MultipartFile.class, int.class, String.class, String.class, String.class, HttpServletRequest.class, User.class, User.class, User.class));// 要点2. 准备对象绑定与类型转换ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);// 要点3. 准备 ModelAndViewContainer 用来存储中间 Model 结果ModelAndViewContainer container = new ModelAndViewContainer();// 要点4. 解析每个参数值for (MethodParameter parameter : handlerMethod.getMethodParameters()) {// 多个解析器组合HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();composite.addResolvers(//                                          false 表示必须有 @RequestParamnew RequestParamMethodArgumentResolver(beanFactory, false),new PathVariableMethodArgumentResolver(),new RequestHeaderMethodArgumentResolver(beanFactory),new ServletCookieValueMethodArgumentResolver(beanFactory),new ExpressionValueMethodArgumentResolver(beanFactory),new ServletRequestMethodArgumentResolver(),new ServletModelAttributeMethodProcessor(false), // 必须有 @ModelAttributenew RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())),new ServletModelAttributeMethodProcessor(true), // 省略了 @ModelAttributenew RequestParamMethodArgumentResolver(beanFactory, true) // 省略 @RequestParam);String annotations = Arrays.stream(parameter.getParameterAnnotations()).map(a -> a.annotationType().getSimpleName()).collect(Collectors.joining());String str = annotations.length() > 0 ? " @" + annotations + " " : " ";parameter.initParameterNameDiscovery(new DefaultParameterNameDiscoverer());if (composite.supportsParameter(parameter)) {// 支持此参数Object v = composite.resolveArgument(parameter, container, new ServletWebRequest(request), factory);
//                System.out.println(v.getClass());System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName() + "->" + v);System.out.println("模型数据为：" + container.getModel());} else {System.out.println("[" + parameter.getParameterIndex() + "] " + str + parameter.getParameterType().getSimpleName() + " " + parameter.getParameterName());}}/*学到了什么a. 每个参数处理器能干啥1) 看是否支持某种参数2) 获取参数的值b. 组合模式在 Spring 中的体现c. @RequestParam, @CookieValue 等注解中的参数名、默认值, 都可以写成活的, 即从 ${ } #{ }中获取*/}private static HttpServletRequest mockRequest() {MockHttpServletRequest request = new MockHttpServletRequest();request.setParameter("name1", "zhangsan");request.setParameter("name2", "lisi");request.addPart(new MockPart("file", "abc", "hello".getBytes(StandardCharsets.UTF_8)));Map<String, String> map = new AntPathMatcher().extractUriTemplateVariables("/test/{id}", "/test/123");System.out.println(map);request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, map);request.setContentType("application/json");request.setCookies(new Cookie("token", "123456"));request.setParameter("name", "张三");request.setParameter("age", "18");request.setContent("""{"name":"李四","age":20}""".getBytes(StandardCharsets.UTF_8));return new StandardServletMultipartResolver().resolveMultipart(request);}static class Controller {public void test(@RequestParam("name1") String name1, // name1=张三String name2,                        // name2=李四@RequestParam("age") int age,        // age=18@RequestParam(name = "home", defaultValue = "${JAVA_HOME}") String home1, // spring 获取数据@RequestParam("file") MultipartFile file, // 上传文件@PathVariable("id") int id,               //  /test/124   /test/{id}@RequestHeader("Content-Type") String header,@CookieValue("token") String token,@Value("${JAVA_HOME}") String home2, // spring 获取数据  ${} #{}HttpServletRequest request,          // request, response, session ...@ModelAttribute("abc") User user1,          // name=zhang&age=18User user2,                          // name=zhang&age=18@RequestBody User user3              // json) {}}static class User {private String name;private int age;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}}
}

收获💡

1. 初步了解 RequestMappingHandlerAdapter 的调用过程
   1. 控制器方法被封装为 HandlerMethod
   2. 准备对象绑定与类型转换
   3. 准备 ModelAndViewContainer 用来存储中间 Model 结果
   4. 解析每个参数值
2. 解析参数依赖的就是各种参数解析器，它们都有两个重要方法
   • supportsParameter 判断是否支持方法参数
   • resolveArgument 解析方法参数
3. 常见参数的解析
   • @RequestParam
   • 省略 @RequestParam
   • @RequestParam(defaultValue)
   • MultipartFile
   • @PathVariable
   • @RequestHeader
   • @CookieValue
   • @Value
   • HttpServletRequest 等
   • @ModelAttribute
   • 省略 @ModelAttribute
   • @RequestBody
4. 组合模式在 Spring 中的体现
5. @RequestParam, @CookieValue 等注解中的参数名、默认值, 都可以写成活的, 即从 ${ } #{ }中获取

22) 参数名解析

演示 - 两种方法获取参数名

代码参考

package com.itheima.a22;import org.springframework.core.LocalVariableTableParameterNameDiscoverer;
import org.springframework.core.StandardReflectionParameterNameDiscoverer;import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.Arrays;/*目标: 如何获取方法参数名, 注意把 a22 目录添加至模块的类路径1. a22 不在 src 是避免 idea 自动编译它下面的类2. spring boot 在编译时会加 -parameters3. 大部分 IDE 编译时都会加 -g*/
public class A22 {public static void main(String[] args) throws NoSuchMethodException, ClassNotFoundException {// 1. 反射获取参数名Method foo = Bean2.class.getMethod("foo", String.class, int.class);/*for (Parameter parameter : foo.getParameters()) {System.out.println(parameter.getName());}*/// 2. 基于 LocalVariableTable 本地变量表LocalVariableTableParameterNameDiscoverer discoverer = new LocalVariableTableParameterNameDiscoverer();String[] parameterNames = discoverer.getParameterNames(foo);System.out.println(Arrays.toString(parameterNames));/*学到了什么a. 如果编译时添加了 -parameters 可以生成参数表, 反射时就可以拿到参数名b. 如果编译时添加了 -g 可以生成调试信息, 但分为两种情况1. 普通类, 会包含局部变量表, 用 asm 可以拿到参数名2. 接口, 不会包含局部变量表, 无法获得参数名 (这也是 MyBatis 在实现 Mapper 接口时为何要提供 @Param 注解来辅助获得参数名)*/}}

收获💡

1. 如果编译时添加了 -parameters 可以生成参数表, 反射时就可以拿到参数名
2. 如果编译时添加了 -g 可以生成调试信息, 但分为两种情况
   • 普通类, 会包含局部变量表, 用 asm 可以拿到参数名
   • 接口, 不会包含局部变量表, 无法获得参数名
     • 这也是 MyBatis 在实现 Mapper 接口时为何要提供 @Param 注解来辅助获得参数名

23) 对象绑定与类型转换

底层第一套转换接口与实现

• Printer 把其它类型转为 String
• Parser 把 String 转为其它类型
• Formatter 综合 Printer 与 Parser 功能
• Converter 把类型 S 转为类型 T
• Printer、Parser、Converter 经过适配转换成 GenericConverter 放入 Converters 集合
• FormattingConversionService 利用其它们实现转换

底层第二套转换接口

• PropertyEditor 把 String 与其它类型相互转换
• PropertyEditorRegistry 可以注册多个 PropertyEditor 对象
• 与第一套接口直接可以通过 FormatterPropertyEditorAdapter 来进行适配

高层接口与实现

• 它们都实现了 TypeConverter 这个高层转换接口，在转换时，会用到 TypeConverter Delegate 委派ConversionService 与 PropertyEditorRegistry 真正执行转换（Facade 门面模式）
  • 首先看是否有自定义转换器, @InitBinder 添加的即属于这种 (用了适配器模式把 Formatter 转为需要的 PropertyEditor)
  • 再看有没有 ConversionService 转换
  • 再利用默认的 PropertyEditor 转换
  • 最后有一些特殊处理
• SimpleTypeConverter 仅做类型转换
• BeanWrapperImpl 为 bean 的属性赋值，当需要时做类型转换，走 Property
• DirectFieldAccessor 为 bean 的属性赋值，当需要时做类型转换，走 Field
• ServletRequestDataBinder 为 bean 的属性执行绑定，当需要时做类型转换，根据 directFieldAccess 选择走 Property 还是 Field，具备校验与获取校验结果功能

演示1 - 类型转换与数据绑定

代码参考

package com.itheima.a23;import org.springframework.beans.SimpleTypeConverter;import java.util.Date;public class TestSimpleConverter {public static void main(String[] args) {// 仅有类型转换的功能SimpleTypeConverter typeConverter = new SimpleTypeConverter();Integer number = typeConverter.convertIfNecessary("13", int.class);Date date = typeConverter.convertIfNecessary("1999/03/04", Date.class);System.out.println(number);System.out.println(date);}
}

package com.itheima.a23;import org.springframework.beans.BeanWrapperImpl;
import org.springframework.beans.SimpleTypeConverter;
import org.springframework.core.GenericTypeResolver;
import org.springframework.format.Formatter;
import org.springframework.format.support.FormatterPropertyEditorAdapter;
import org.springframework.format.support.FormattingConversionService;import java.util.Date;public class TestBeanWrapper {public static void main(String[] args) {// 利用反射原理, 为 bean 的属性赋值MyBean target = new MyBean();BeanWrapperImpl wrapper = new BeanWrapperImpl(target);wrapper.setPropertyValue("a", "10");wrapper.setPropertyValue("b", "hello");wrapper.setPropertyValue("c", "1999/03/04");System.out.println(target);}static class MyBean {private int a;private String b;private Date c;public int getA() {return a;}public void setA(int a) {this.a = a;}public String getB() {return b;}public void setB(String b) {this.b = b;}public Date getC() {return c;}public void setC(Date c) {this.c = c;}@Overridepublic String toString() {return "MyBean{" +"a=" + a +", b='" + b + '\'' +", c=" + c +'}';}}
}

package com.itheima.a23;import org.springframework.beans.MutablePropertyValues;
import org.springframework.validation.DataBinder;import java.util.Date;public class TestDataBinder {public static void main(String[] args) {// 执行数据绑定MyBean target = new MyBean();DataBinder dataBinder = new DataBinder(target);dataBinder.initDirectFieldAccess();MutablePropertyValues pvs = new MutablePropertyValues();pvs.add("a", "10");pvs.add("b", "hello");pvs.add("c", "1999/03/04");dataBinder.bind(pvs);System.out.println(target);}static class MyBean {private int a;private String b;private Date c;@Overridepublic String toString() {return "MyBean{" +"a=" + a +", b='" + b + '\'' +", c=" + c +'}';}}
}

package com.itheima.a23;import org.springframework.beans.MutablePropertyValues;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.validation.DataBinder;
import org.springframework.web.bind.ServletRequestDataBinder;
import org.springframework.web.bind.ServletRequestParameterPropertyValues;import java.util.Date;public class TestServletDataBinder {public static void main(String[] args) {// web 环境下数据绑定MyBean target = new MyBean();ServletRequestDataBinder dataBinder = new ServletRequestDataBinder(target);MockHttpServletRequest request = new MockHttpServletRequest();request.setParameter("a", "10");request.setParameter("b", "hello");request.setParameter("c", "1999/03/04");dataBinder.bind(new ServletRequestParameterPropertyValues(request));System.out.println(target);}static class MyBean {private int a;private String b;private Date c;public int getA() {return a;}public void setA(int a) {this.a = a;}public String getB() {return b;}public void setB(String b) {this.b = b;}public Date getC() {return c;}public void setC(Date c) {this.c = c;}@Overridepublic String toString() {return "MyBean{" +"a=" + a +", b='" + b + '\'' +", c=" + c +'}';}}
}

package com.itheima.a23;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.GenericTypeResolver;
import org.springframework.format.Formatter;import java.lang.reflect.Type;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;public class MyDateFormatter implements Formatter<Date> {private static final Logger log = LoggerFactory.getLogger(MyDateFormatter.class);private final String desc;public MyDateFormatter(String desc) {this.desc = desc;}@Overridepublic String print(Date date, Locale locale) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy|MM|dd");return sdf.format(date);}@Overridepublic Date parse(String text, Locale locale) throws ParseException {log.debug(">>>>>> 进入了: {}", desc);SimpleDateFormat sdf = new SimpleDateFormat("yyyy|MM|dd");return sdf.parse(text);}}

收获💡

基本的类型转换与数据绑定用法

• SimpleTypeConverter
• BeanWrapperImpl
• DirectFieldAccessor
• ServletRequestDataBinder

演示2 - 数据绑定工厂

代码参考

package com.itheima.a23;import org.springframework.boot.convert.ApplicationConversionService;
import org.springframework.format.annotation.DateTimeFormat;
import org.springframework.format.support.DefaultFormattingConversionService;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.web.bind.ServletRequestParameterPropertyValues;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.annotation.InitBinder;
import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.servlet.mvc.method.annotation.ServletRequestDataBinderFactory;import java.util.Date;public class TestServletDataBinderFactory {public static void main(String[] args) throws Exception {MockHttpServletRequest request = new MockHttpServletRequest();request.setParameter("birthday", "1999|01|02");request.setParameter("address.name", "西安");User target = new User();// "1. 用工厂, 无转换功能"
//        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);// "2. 用 @InitBinder 转换"          PropertyEditorRegistry PropertyEditor
//        InvocableHandlerMethod method = new InvocableHandlerMethod(new MyController(), MyController.class.getMethod("aaa", WebDataBinder.class));
//        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(List.of(method), null);// "3. 用 ConversionService 转换"    ConversionService Formatter
//        FormattingConversionService service = new FormattingConversionService();
//        service.addFormatter(new MyDateFormatter("用 ConversionService 方式扩展转换功能"));
//        ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
//        initializer.setConversionService(service);
//        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, initializer);// "4. 同时加了 @InitBinder 和 ConversionService"
//        InvocableHandlerMethod method = new InvocableHandlerMethod(new MyController(), MyController.class.getMethod("aaa", WebDataBinder.class));
//
//        FormattingConversionService service = new FormattingConversionService();
//        service.addFormatter(new MyDateFormatter("用 ConversionService 方式扩展转换功能"));
//        ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();
//        initializer.setConversionService(service);
//
//        ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(List.of(method), initializer);// "5. 使用默认 ConversionService 转换"ApplicationConversionService service = new ApplicationConversionService();ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();initializer.setConversionService(service);ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, initializer);WebDataBinder dataBinder = factory.createBinder(new ServletWebRequest(request), target, "user");dataBinder.bind(new ServletRequestParameterPropertyValues(request));System.out.println(target);}static class MyController {@InitBinderpublic void aaa(WebDataBinder dataBinder) {// 扩展 dataBinder 的转换器dataBinder.addCustomFormatter(new MyDateFormatter("用 @InitBinder 方式扩展的"));}}public static class User {@DateTimeFormat(pattern = "yyyy|MM|dd")private Date birthday;private Address address;public Address getAddress() {return address;}public void setAddress(Address address) {this.address = address;}public Date getBirthday() {return birthday;}public void setBirthday(Date birthday) {this.birthday = birthday;}@Overridepublic String toString() {return "User{" +"birthday=" + birthday +", address=" + address +'}';}}public static class Address {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Address{" +"name='" + name + '\'' +'}';}}
}

收获💡

ServletRequestDataBinderFactory 的用法和扩展点

1. 可以解析控制器的 @InitBinder 标注方法作为扩展点，添加自定义转换器
   • 控制器私有范围
2. 可以通过 ConfigurableWebBindingInitializer 配置 ConversionService 作为扩展点，添加自定义转换器
   • 公共范围
3. 同时加了 @InitBinder 和 ConversionService 的转换优先级
   1. 优先采用 @InitBinder 的转换器
   2. 其次使用 ConversionService 的转换器
   3. 使用默认转换器
   4. 特殊处理（例如有参构造）

演示3 - 获取泛型参数

代码参考

package com.itheima.a23.sub;import org.springframework.core.GenericTypeResolver;
import org.springframework.core.ResolvableType;import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;public class TestGenericType {public static void main(String[] args) {// 小技巧// 1. java apiSystem.out.println(">>>>>>>>>>>>>>>>>>>>>>>");Type type = TeacherDao.class.getGenericSuperclass();System.out.println(type);if (type instanceof ParameterizedType parameterizedType) {System.out.println(parameterizedType.getActualTypeArguments()[0]);}// 2. spring api 1System.out.println(">>>>>>>>>>>>>>>>>>>>>>>");Class<?> t = GenericTypeResolver.resolveTypeArgument(TeacherDao.class, BaseDao.class);System.out.println(t);// 3. spring api 2System.out.println(">>>>>>>>>>>>>>>>>>>>>>>");System.out.println(ResolvableType.forClass(TeacherDao.class).getSuperType().getGeneric().resolve());}}

收获💡

1. java api 获取泛型参数
2. spring api 获取泛型参数

24) @ControllerAdvice 之 @InitBinder

演示 - 准备 @InitBinder

准备 @InitBinder 在整个 HandlerAdapter 调用过程中所处的位置

• RequestMappingHandlerAdapter 在图中缩写为 HandlerAdapter
• HandlerMethodArgumentResolverComposite 在图中缩写为 ArgumentResolvers
• HandlerMethodReturnValueHandlerComposite 在图中缩写为 ReturnValueHandlers

package com.itheima.a24;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.web.method.ControllerAdviceBean;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;/*@InitBinder 的来源*/
public class A24 {private static final Logger log = LoggerFactory.getLogger(A24.class);public static void main(String[] args) throws Exception {/*@InitBinder 的来源有两个1. @ControllerAdvice 中 @InitBinder 标注的方法，由 RequestMappingHandlerAdapter 在初始化时解析并记录2. @Controller 中 @InitBinder 标注的方法，由 RequestMappingHandlerAdapter 会在控制器方法首次执行时解析并记录*/AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(WebConfig.class);RequestMappingHandlerAdapter handlerAdapter = new RequestMappingHandlerAdapter();handlerAdapter.setApplicationContext(context);handlerAdapter.afterPropertiesSet();log.debug("1. 刚开始...");showBindMethods(handlerAdapter);Method getDataBinderFactory = RequestMappingHandlerAdapter.class.getDeclaredMethod("getDataBinderFactory", HandlerMethod.class);getDataBinderFactory.setAccessible(true);log.debug("2. 模拟调用 Controller1 的 foo 方法时 ...");getDataBinderFactory.invoke(handlerAdapter, new HandlerMethod(new WebConfig.Controller1(), WebConfig.Controller1.class.getMethod("foo")));showBindMethods(handlerAdapter);log.debug("3. 模拟调用 Controller2 的 bar 方法时 ...");getDataBinderFactory.invoke(handlerAdapter, new HandlerMethod(new WebConfig.Controller2(), WebConfig.Controller2.class.getMethod("bar")));showBindMethods(handlerAdapter);context.close();/*学到了什么a. Method 对象的获取利用了缓存来进行加速b. 绑定器工厂的扩展点(advice 之一), 通过 @InitBinder 扩展类型转换器*/}@SuppressWarnings("all")private static void showBindMethods(RequestMappingHandlerAdapter handlerAdapter) throws NoSuchFieldException, IllegalAccessException {Field initBinderAdviceCache = RequestMappingHandlerAdapter.class.getDeclaredField("initBinderAdviceCache");initBinderAdviceCache.setAccessible(true);Map<ControllerAdviceBean, Set<Method>> globalMap = (Map<ControllerAdviceBean, Set<Method>>) initBinderAdviceCache.get(handlerAdapter);log.debug("全局的 @InitBinder 方法 {}",globalMap.values().stream().flatMap(ms -> ms.stream().map(m -> m.getName())).collect(Collectors.toList()));Field initBinderCache = RequestMappingHandlerAdapter.class.getDeclaredField("initBinderCache");initBinderCache.setAccessible(true);Map<Class<?>, Set<Method>> controllerMap = (Map<Class<?>, Set<Method>>) initBinderCache.get(handlerAdapter);log.debug("控制器的 @InitBinder 方法 {}",controllerMap.entrySet().stream().flatMap(e -> e.getValue().stream().map(v -> e.getKey().getSimpleName() + "." + v.getName())).collect(Collectors.toList()));}
}

收获💡

1. RequestMappingHandlerAdapter 初始化时会解析 @ControllerAdvice 中的 @InitBinder 方法
2. RequestMappingHandlerAdapter 会以类为单位，在该类首次使用时，解析此类的 @InitBinder 方法
3. 以上两种 @InitBinder 的解析结果都会缓存来避免重复解析
4. 控制器方法调用时，会综合利用本类的 @InitBinder 方法和 @ControllerAdvice 中的 @InitBinder 方法创建绑定工厂

25) 控制器方法执行流程

图1

HandlerMethod 需要

• bean 即是哪个 Controller
• method 即是 Controller 中的哪个方法

ServletInvocableHandlerMethod 需要

• WebDataBinderFactory 负责对象绑定、类型转换
• ParameterNameDiscoverer 负责参数名解析
• HandlerMethodArgumentResolverComposite 负责解析参数
• HandlerMethodReturnValueHandlerComposite 负责处理返回值

图2

图3

26) @ControllerAdvice 之 @ModelAttribute

演示 - 准备 @ModelAttribute

代码参考

package com.itheima.a26;import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.core.DefaultParameterNameDiscoverer;
import org.springframework.http.HttpStatus;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.support.DefaultSessionAttributeStore;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.annotation.*;
import org.springframework.web.method.support.HandlerMethodArgumentResolverComposite;
import org.springframework.web.method.support.InvocableHandlerMethod;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.method.annotation.*;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.List;import static com.itheima.a26.WebConfig.*;public class A26 {public static void main(String[] args) throws Exception {AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(WebConfig.class);RequestMappingHandlerAdapter adapter = new RequestMappingHandlerAdapter();adapter.setApplicationContext(context);adapter.afterPropertiesSet();MockHttpServletRequest request = new MockHttpServletRequest();request.setParameter("name", "张三");/*现在可以通过 ServletInvocableHandlerMethod 把这些整合在一起, 并完成控制器方法的调用, 如下*/ServletInvocableHandlerMethod handlerMethod = new ServletInvocableHandlerMethod(new Controller1(), Controller1.class.getMethod("foo", User.class));ServletRequestDataBinderFactory factory = new ServletRequestDataBinderFactory(null, null);handlerMethod.setDataBinderFactory(factory);handlerMethod.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());handlerMethod.setHandlerMethodArgumentResolvers(getArgumentResolvers(context));ModelAndViewContainer container = new ModelAndViewContainer();// 获取模型工厂方法Method getModelFactory = RequestMappingHandlerAdapter.class.getDeclaredMethod("getModelFactory", HandlerMethod.class, WebDataBinderFactory.class);getModelFactory.setAccessible(true);ModelFactory modelFactory = (ModelFactory) getModelFactory.invoke(adapter, handlerMethod, factory);// 初始化模型数据modelFactory.initModel(new ServletWebRequest(request), container, handlerMethod);handlerMethod.invokeAndHandle(new ServletWebRequest(request), container);System.out.println(container.getModel());context.close();/*学到了什么a. 控制器方法是如何调用的b. 模型数据如何产生c. advice 之二, @ModelAttribute 补充模型数据*/}public static HandlerMethodArgumentResolverComposite getArgumentResolvers(AnnotationConfigApplicationContext context) {HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();composite.addResolvers(new RequestParamMethodArgumentResolver(context.getDefaultListableBeanFactory(), false),new PathVariableMethodArgumentResolver(),new RequestHeaderMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ServletCookieValueMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ExpressionValueMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ServletRequestMethodArgumentResolver(),new ServletModelAttributeMethodProcessor(false),new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())),new ServletModelAttributeMethodProcessor(true),new RequestParamMethodArgumentResolver(context.getDefaultListableBeanFactory(), true));return composite;}}

package com.itheima.a26;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpStatus;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;@Configuration
public class WebConfig {@ControllerAdvicestatic class MyControllerAdvice {@ModelAttribute("a")public String aa() {return "aa";}}@Controllerstatic class Controller1 {@ModelAttribute("b")public String aa() {return "bb";}@ResponseStatus(HttpStatus.OK)public ModelAndView foo(@ModelAttribute("u") User user) {System.out.println("foo");return null;}}static class User {private String name;public void setName(String name) {this.name = name;}public String getName() {return name;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +'}';}}
}

准备 @ModelAttribute 在整个 HandlerAdapter 调用过程中所处的位置

收获💡

1. RequestMappingHandlerAdapter 初始化时会解析 @ControllerAdvice 中的 @ModelAttribute 方法
2. RequestMappingHandlerAdapter 会以类为单位，在该类首次使用时，解析此类的 @ModelAttribute 方法
3. 以上两种 @ModelAttribute 的解析结果都会缓存来避免重复解析
4. 控制器方法调用时，会综合利用本类的 @ModelAttribute 方法和 @ControllerAdvice 中的 @ModelAttribute 方法创建模型工厂

27) 返回值处理器

演示 - 常见返回值处理器

代码参考

package com.itheima.a27;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.mvc.method.annotation.*;
import org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator;
import org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver;
import org.springframework.web.util.UrlPathHelper;import java.lang.reflect.Method;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Locale;/*目标: 解析控制器方法的返回值常见的返回值处理器org.springframework.web.se[e-mail]@5d1e09bcorg.springframewor[e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail][e-mail]@6ff37443org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor@65cc8228*/
public class A27 {private static final Logger log = LoggerFactory.getLogger(A27.class);public static void main(String[] args) throws Exception {AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(WebConfig.class);// 1. 测试返回值类型为 ModelAndView// 2. 测试返回值类型为 String 时, 把它当做视图名// 3. 测试返回值添加了 @ModelAttribute 注解时, 此时需找到默认视图名// 4. 测试返回值不加 @ModelAttribute 注解且返回非简单类型时, 此时需找到默认视图名// 5. 测试返回值类型为 ResponseEntity 时, 此时不走视图流程// 6. 测试返回值类型为 HttpHeaders 时, 此时不走视图流程// 7. 测试返回值添加了 @ResponseBody 注解时, 此时不走视图流程test7(context);/*学到了什么a. 每个返回值处理器能干啥1) 看是否支持某种返回值2) 返回值或作为模型、或作为视图名、或作为响应体 ...b. 组合模式在 Spring 中的体现 + 1*/}private static void test7(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test7");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();ServletWebRequest webRequest = new ServletWebRequest(request, response);if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());if (!container.isRequestHandled()) {renderView(context, container, webRequest); // 渲染视图} else {for (String name : response.getHeaderNames()) {System.out.println(name + "=" + response.getHeader(name));}System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));}}}private static void test6(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test6");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();ServletWebRequest webRequest = new ServletWebRequest(request, response);if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());if (!container.isRequestHandled()) {renderView(context, container, webRequest); // 渲染视图} else {for (String name : response.getHeaderNames()) {System.out.println(name + "=" + response.getHeader(name));}System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));}}}private static void test5(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test5");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();ServletWebRequest webRequest = new ServletWebRequest(request, response);if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());if (!container.isRequestHandled()) {renderView(context, container, webRequest); // 渲染视图} else {System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));}}}private static void test4(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test4");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();MockHttpServletRequest request = new MockHttpServletRequest();request.setRequestURI("/test4");UrlPathHelper.defaultInstance.resolveAndCacheLookupPath(request);ServletWebRequest webRequest = new ServletWebRequest(request, new MockHttpServletResponse());if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());renderView(context, container, webRequest); // 渲染视图}}private static void test3(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test3");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();MockHttpServletRequest request = new MockHttpServletRequest();request.setRequestURI("/test3");UrlPathHelper.defaultInstance.resolveAndCacheLookupPath(request);ServletWebRequest webRequest = new ServletWebRequest(request, new MockHttpServletResponse());if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());renderView(context, container, webRequest); // 渲染视图}}private static void test2(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test2");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();ServletWebRequest webRequest = new ServletWebRequest(new MockHttpServletRequest(), new MockHttpServletResponse());if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());renderView(context, container, webRequest); // 渲染视图}}private static void test1(AnnotationConfigApplicationContext context) throws Exception {Method method = Controller.class.getMethod("test1");Controller controller = new Controller();Object returnValue = method.invoke(controller); // 获取返回值HandlerMethod methodHandle = new HandlerMethod(controller, method);ModelAndViewContainer container = new ModelAndViewContainer();HandlerMethodReturnValueHandlerComposite composite = getReturnValueHandler();ServletWebRequest webRequest = new ServletWebRequest(new MockHttpServletRequest(), new MockHttpServletResponse());if (composite.supportsReturnType(methodHandle.getReturnType())) { // 检查是否支持此类型的返回值composite.handleReturnValue(returnValue, methodHandle.getReturnType(), container, webRequest);System.out.println(container.getModel());System.out.println(container.getViewName());renderView(context, container, webRequest); // 渲染视图}}public static HandlerMethodReturnValueHandlerComposite getReturnValueHandler() {HandlerMethodReturnValueHandlerComposite composite = new HandlerMethodReturnValueHandlerComposite();composite.addHandler(new ModelAndViewMethodReturnValueHandler());composite.addHandler(new ViewNameMethodReturnValueHandler());composite.addHandler(new ServletModelAttributeMethodProcessor(false));composite.addHandler(new HttpEntityMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())));composite.addHandler(new HttpHeadersReturnValueHandler());composite.addHandler(new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())));composite.addHandler(new ServletModelAttributeMethodProcessor(true));return composite;}@SuppressWarnings("all")private static void renderView(AnnotationConfigApplicationContext context, ModelAndViewContainer container,ServletWebRequest webRequest) throws Exception {log.debug(">>>>>> 渲染视图");FreeMarkerViewResolver resolver = context.getBean(FreeMarkerViewResolver.class);String viewName = container.getViewName() != null ? container.getViewName() : new DefaultRequestToViewNameTranslator().getViewName(webRequest.getRequest());log.debug("没有获取到视图名, 采用默认视图名: {}", viewName);// 每次渲染时, 会产生新的视图对象, 它并非被 Spring 所管理, 但确实借助了 Spring 容器来执行初始化View view = resolver.resolveViewName(viewName, Locale.getDefault());view.render(container.getModel(), webRequest.getRequest(), webRequest.getResponse());System.out.println(new String(((MockHttpServletResponse) webRequest.getResponse()).getContentAsByteArray(), StandardCharsets.UTF_8));}static class Controller {private static final Logger log = LoggerFactory.getLogger(Controller.class);public ModelAndView test1() {log.debug("test1()");ModelAndView mav = new ModelAndView("view1");mav.addObject("name", "张三");return mav;}public String test2() {log.debug("test2()");return "view2";}@ModelAttribute
//        @RequestMapping("/test3")public User test3() {log.debug("test3()");return new User("李四", 20);}public User test4() {log.debug("test4()");return new User("王五", 30);}public HttpEntity<User> test5() {log.debug("test5()");return new HttpEntity<>(new User("赵六", 40));}public HttpHeaders test6() {log.debug("test6()");HttpHeaders headers = new HttpHeaders();headers.add("Content-Type", "text/html");return headers;}@ResponseBodypublic User test7() {log.debug("test7()");return new User("钱七", 50);}}// 必须用 public 修饰, 否则 freemarker 渲染其 name, age 属性时失败public static class User {private String name;private int age;public User(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}}
}

package com.itheima.a27;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.view.AbstractUrlBasedView;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer;
import org.springframework.web.servlet.view.freemarker.FreeMarkerView;
import org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver;@Configuration
public class WebConfig {@Beanpublic FreeMarkerConfigurer freeMarkerConfigurer() {FreeMarkerConfigurer configurer = new FreeMarkerConfigurer();configurer.setDefaultEncoding("utf-8");configurer.setTemplateLoaderPath("classpath:templates");return configurer;}@Bean // FreeMarkerView 在借助 Spring 初始化时，会要求 web 环境才会走 setConfiguration, 这里想办法去掉了 web 环境的约束public FreeMarkerViewResolver viewResolver(FreeMarkerConfigurer configurer) {FreeMarkerViewResolver resolver = new FreeMarkerViewResolver() {@Overrideprotected AbstractUrlBasedView instantiateView() {FreeMarkerView view = new FreeMarkerView() {@Overrideprotected boolean isContextRequired() {return false;}};view.setConfiguration(configurer.getConfiguration());return view;}};resolver.setContentType("text/html;charset=utf-8");resolver.setPrefix("/");resolver.setSuffix(".ftl");resolver.setExposeSpringMacroHelpers(false);return resolver;}
}

收获💡

1. 常见的返回值处理器
   • ModelAndView，分别获取其模型和视图名，放入 ModelAndViewContainer
   • 返回值类型为 String 时，把它当做视图名，放入 ModelAndViewContainer
   • 返回值添加了 @ModelAttribute 注解时，将返回值作为模型，放入 ModelAndViewContainer
     • 此时需找到默认视图名
   • 返回值省略 @ModelAttribute 注解且返回非简单类型时，将返回值作为模型，放入 ModelAndViewContainer
     • 此时需找到默认视图名
   • 返回值类型为 ResponseEntity 时
     • 此时走 MessageConverter，并设置 ModelAndViewContainer.requestHandled 为 true
   • 返回值类型为 HttpHeaders 时
     • 会设置 ModelAndViewContainer.requestHandled 为 true
   • 返回值添加了 @ResponseBody 注解时
     • 此时走 MessageConverter，并设置 ModelAndViewContainer.requestHandled 为 true
2. 组合模式在 Spring 中的体现 + 1

28) MessageConverter

演示 - MessageConverter 的作用

代码参考

package com.itheima.a28;import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.springframework.core.MethodParameter;
import org.springframework.http.MediaType;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter;
import org.springframework.mock.http.MockHttpInputMessage;
import org.springframework.mock.http.MockHttpOutputMessage;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor;import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.List;public class A28 {public static void main(String[] args) throws IOException, NoSuchMethodException, HttpMediaTypeNotAcceptableException {
//        test1();
//        test2();
//        test3();test4();/*学到了什么a. MessageConverter 的作用, @ResponseBody 是返回值处理器解析的, 但具体转换工作是 MessageConverter 做的b. 如何选择 MediaType- 首先看 @RequestMapping 上有没有指定- 其次看 request 的 Accept 头有没有指定- 最后按 MessageConverter 的顺序, 谁能谁先转换*/}private static void test4() throws IOException, HttpMediaTypeNotAcceptableException, NoSuchMethodException {MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();ServletWebRequest webRequest = new ServletWebRequest(request, response);request.addHeader("Accept", "application/xml");response.setContentType("application/json");RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter(), new MappingJackson2XmlHttpMessageConverter()));processor.handleReturnValue(new User("张三", 18),new MethodParameter(A28.class.getMethod("user"), -1),new ModelAndViewContainer(),webRequest);System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));}@ResponseBody@RequestMapping(produces = "application/json")public User user() {return null;}private static void test3() throws IOException {MockHttpInputMessage message = new MockHttpInputMessage("""{"name":"李四","age":20}""".getBytes(StandardCharsets.UTF_8));MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();if (converter.canRead(User.class, MediaType.APPLICATION_JSON)) {Object read = converter.read(User.class, message);System.out.println(read);}}private static void test2() throws IOException {MockHttpOutputMessage message = new MockHttpOutputMessage();MappingJackson2XmlHttpMessageConverter converter = new MappingJackson2XmlHttpMessageConverter();if (converter.canWrite(User.class, MediaType.APPLICATION_XML)) {converter.write(new User("李四", 20), MediaType.APPLICATION_XML, message);System.out.println(message.getBodyAsString());}}public static void test1() throws IOException {MockHttpOutputMessage message = new MockHttpOutputMessage();MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();if (converter.canWrite(User.class, MediaType.APPLICATION_JSON)) {converter.write(new User("张三", 18), MediaType.APPLICATION_JSON, message);System.out.println(message.getBodyAsString());}}public static class User {private String name;private int age;@JsonCreatorpublic User(@JsonProperty("name") String name, @JsonProperty("age") int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}}
}

收获💡

1. MessageConverter 的作用
   • @ResponseBody 是返回值处理器解析的
   • 但具体转换工作是 MessageConverter 做的
2. 如何选择 MediaType
   • 首先看 @RequestMapping 上有没有指定
   • 其次看 request 的 Accept 头有没有指定
   • 最后按 MessageConverter 的顺序, 谁能谁先转换

29) @ControllerAdvice 之 ResponseBodyAdvice

演示 - ResponseBodyAdvice 增强

代码参考

package com.itheima.a29;import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.core.DefaultParameterNameDiscoverer;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.ControllerAdviceBean;
import org.springframework.web.method.annotation.ExpressionValueMethodArgumentResolver;
import org.springframework.web.method.annotation.RequestHeaderMethodArgumentResolver;
import org.springframework.web.method.annotation.RequestParamMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodArgumentResolverComposite;
import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.mvc.method.annotation.*;import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;public class A29 {// {"name":"王五","age":18}// {"code":xx, "msg":xx, data: {"name":"王五","age":18} }public static void main(String[] args) throws Exception {AnnotationConfigApplicationContext context =new AnnotationConfigApplicationContext(WebConfig.class);ServletInvocableHandlerMethod handlerMethod = new ServletInvocableHandlerMethod(context.getBean(WebConfig.MyController.class),WebConfig.MyController.class.getMethod("user"));handlerMethod.setDataBinderFactory(new ServletRequestDataBinderFactory(Collections.emptyList(), null));handlerMethod.setParameterNameDiscoverer(new DefaultParameterNameDiscoverer());handlerMethod.setHandlerMethodArgumentResolvers(getArgumentResolvers(context));handlerMethod.setHandlerMethodReturnValueHandlers(getReturnValueHandlers(context));MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();ModelAndViewContainer container = new ModelAndViewContainer();handlerMethod.invokeAndHandle(new ServletWebRequest(request, response), container);System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));/*学到了什么a. advice 之三, ResponseBodyAdvice 返回响应体前包装*/}public static HandlerMethodArgumentResolverComposite getArgumentResolvers(AnnotationConfigApplicationContext context) {HandlerMethodArgumentResolverComposite composite = new HandlerMethodArgumentResolverComposite();composite.addResolvers(new RequestParamMethodArgumentResolver(context.getDefaultListableBeanFactory(), false),new PathVariableMethodArgumentResolver(),new RequestHeaderMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ServletCookieValueMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ExpressionValueMethodArgumentResolver(context.getDefaultListableBeanFactory()),new ServletRequestMethodArgumentResolver(),new ServletModelAttributeMethodProcessor(false),new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())),new ServletModelAttributeMethodProcessor(true),new RequestParamMethodArgumentResolver(context.getDefaultListableBeanFactory(), true));return composite;}public static HandlerMethodReturnValueHandlerComposite getReturnValueHandlers(AnnotationConfigApplicationContext context) {// 添加 adviceList<ControllerAdviceBean> annotatedBeans = ControllerAdviceBean.findAnnotatedBeans(context);List<Object> collect = annotatedBeans.stream().filter(b -> ResponseBodyAdvice.class.isAssignableFrom(b.getBeanType())).collect(Collectors.toList());HandlerMethodReturnValueHandlerComposite composite = new HandlerMethodReturnValueHandlerComposite();composite.addHandler(new ModelAndViewMethodReturnValueHandler());composite.addHandler(new ViewNameMethodReturnValueHandler());composite.addHandler(new ServletModelAttributeMethodProcessor(false));composite.addHandler(new HttpEntityMethodProcessor(List.of(new MappingJackson2HttpMessageConverter())));composite.addHandler(new HttpHeadersReturnValueHandler());composite.addHandler(new RequestResponseBodyMethodProcessor(List.of(new MappingJackson2HttpMessageConverter()), collect));composite.addHandler(new ServletModelAttributeMethodProcessor(true));return composite;}
}

package com.itheima.a29;import org.springframework.context.annotation.Configuration;
import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;@Configuration
public class WebConfig {@ControllerAdvicestatic class MyControllerAdvice implements ResponseBodyAdvice<Object> {// 满足条件才转换public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {if (returnType.getMethodAnnotation(ResponseBody.class) != null ||AnnotationUtils.findAnnotation(returnType.getContainingClass(), ResponseBody.class) != null) {
//                returnType.getContainingClass().isAnnotationPresent(ResponseBody.class)) {return true;}return false;}// 将 User 或其它类型统一为 Result 类型public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {if (body instanceof Result) {return body;}return Result.ok(body);}}// @Controller// @ResponseBody@RestControllerpublic static class MyController {public User user() {return new User("王五", 18);}}public static class User {private String name;private int age;public User(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}
}

ResponseBodyAdvice 增强 在整个 HandlerAdapter 调用过程中所处的位置

收获💡

1. ResponseBodyAdvice 返回响应体前包装

30) 异常解析器

演示 - ExceptionHandlerExceptionResolver

代码参考

package com.itheima.a30;import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;public class A30 {public static void main(String[] args) throws NoSuchMethodException {ExceptionHandlerExceptionResolver resolver = new ExceptionHandlerExceptionResolver();resolver.setMessageConverters(List.of(new MappingJackson2HttpMessageConverter()));resolver.afterPropertiesSet();MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();// 1.测试 json
//        HandlerMethod handlerMethod = new HandlerMethod(new Controller1(), Controller1.class.getMethod("foo"));
//        Exception e = new ArithmeticException("被零除");
//        resolver.resolveException(request, response, handlerMethod, e);
//        System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));// 2.测试 mav
//        HandlerMethod handlerMethod = new HandlerMethod(new Controller2(), Controller2.class.getMethod("foo"));
//        Exception e = new ArithmeticException("被零除");
//        ModelAndView mav = resolver.resolveException(request, response, handlerMethod, e);
//        System.out.println(mav.getModel());
//        System.out.println(mav.getViewName());// 3.测试嵌套异常
//        HandlerMethod handlerMethod = new HandlerMethod(new Controller3(), Controller3.class.getMethod("foo"));
//        Exception e = new Exception("e1", new RuntimeException("e2", new IOException("e3")));
//        resolver.resolveException(request, response, handlerMethod, e);
//        System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));// 4.测试异常处理方法参数解析HandlerMethod handlerMethod = new HandlerMethod(new Controller4(), Controller4.class.getMethod("foo"));Exception e = new Exception("e1");resolver.resolveException(request, response, handlerMethod, e);System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));/*学到了什么a. ExceptionHandlerExceptionResolver 能够重用参数解析器、返回值处理器，实现组件重用b. 能够支持嵌套异常*/}static class Controller1 {public void foo() {}@ExceptionHandler@ResponseBodypublic Map<String, Object> handle(ArithmeticException e) {return Map.of("error", e.getMessage());}}static class Controller2 {public void foo() {}@ExceptionHandlerpublic ModelAndView handle(ArithmeticException e) {return new ModelAndView("test2", Map.of("error", e.getMessage()));}}static class Controller3 {public void foo() {}@ExceptionHandler@ResponseBodypublic Map<String, Object> handle(IOException e3) {return Map.of("error", e3.getMessage());}}static class Controller4 {public void foo() {}@ExceptionHandler@ResponseBodypublic Map<String, Object> handler(Exception e, HttpServletRequest request) {System.out.println(request);return Map.of("error", e.getMessage());}}
}

收获💡

1. 它能够重用参数解析器、返回值处理器，实现组件重用
2. 它能够支持嵌套异常

31) @ControllerAdvice 之 @ExceptionHandler

演示 - 准备 @ExceptionHandler

代码参考

package com.itheima.a31;import com.itheima.a30.A30;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.mock.web.MockHttpServletRequest;
import org.springframework.mock.web.MockHttpServletResponse;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver;import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Map;public class A31 {public static void main(String[] args) throws NoSuchMethodException {MockHttpServletRequest request = new MockHttpServletRequest();MockHttpServletResponse response = new MockHttpServletResponse();//        ExceptionHandlerExceptionResolver resolver = new ExceptionHandlerExceptionResolver();
//        resolver.setMessageConverters(List.of(new MappingJackson2HttpMessageConverter()));
//        resolver.afterPropertiesSet();AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(WebConfig.class);ExceptionHandlerExceptionResolver resolver = context.getBean(ExceptionHandlerExceptionResolver.class);HandlerMethod handlerMethod = new HandlerMethod(new Controller5(), Controller5.class.getMethod("foo"));Exception e = new Exception("e1");resolver.resolveException(request, response, handlerMethod, e);System.out.println(new String(response.getContentAsByteArray(), StandardCharsets.UTF_8));}static class Controller5 {public void foo() {}}
}

package com.itheima.a31;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver;import java.util.List;
import java.util.Map;@Configuration
public class WebConfig {@ControllerAdvicestatic class MyControllerAdvice {@ExceptionHandler@ResponseBodypublic Map<String, Object> handle(Exception e) {return Map.of("error", e.getMessage());}}@Beanpublic ExceptionHandlerExceptionResolver resolver() {ExceptionHandlerExceptionResolver resolver = new ExceptionHandlerExceptionResolver();resolver.setMessageConverters(List.of(new MappingJackson2HttpMessageConverter()));return resolver;}
}

收获💡

1. ExceptionHandlerExceptionResolver 初始化时会解析 @ControllerAdvice 中的 @ExceptionHandler 方法
2. ExceptionHandlerExceptionResolver 会以类为单位，在该类首次处理异常时，解析此类的 @ExceptionHandler 方法
3. 以上两种 @ExceptionHandler 的解析结果都会缓存来避免重复解析

32) Tomcat 异常处理

• 我们知道 @ExceptionHandler 只能处理发生在 mvc 流程中的异常，例如控制器内、拦截器内，那么如果是 Filter 出现了异常，如何进行处理呢？

• 在 Spring Boot 中，是这么实现的：

  1. 因为内嵌了 Tomcat 容器，因此可以配置 Tomcat 的错误页面，Filter 与 错误页面之间是通过请求转发跳转的，可以在这里做手脚
  2. 先通过 ErrorPageRegistrarBeanPostProcessor 这个后处理器配置错误页面地址，默认为 /error 也可以通过 ${server.error.path} 进行配置
  3. 当 Filter 发生异常时，不会走 Spring 流程，但会走 Tomcat 的错误处理，于是就希望转发至 /error 这个地址
     • 当然，如果没有 @ExceptionHandler，那么最终也会走到 Tomcat 的错误处理
  4. Spring Boot 又提供了一个 BasicErrorController，它就是一个标准 @Controller，@RequestMapping 配置为 /error，所以处理异常的职责就又回到了 Spring
  5. 异常信息由于会被 Tomcat 放入 request 作用域，因此 BasicErrorController 里也能获取到
  6. 具体异常信息会由 DefaultErrorAttributes 封装好
  7. BasicErrorController 通过 Accept 头判断需要生成哪种 MediaType 的响应
     • 如果要的不是 text/html，走 MessageConverter 流程
     • 如果需要 text/html，走 mvc 流程，此时又分两种情况
       • 配置了 ErrorViewResolver，根据状态码去找 View
       • 没配置或没找到，用 BeanNameViewResolver 根据一个固定为 error 的名字找到 View，即所谓的 WhitelabelErrorView

评价

• 一个错误处理搞得这么复杂，就问恶心不？

演示1 - 错误页处理

关键代码

@Bean // ⬅️修改了 Tomcat 服务器默认错误地址, 出错时使用请求转发方式跳转
public ErrorPageRegistrar errorPageRegistrar() {return webServerFactory -> webServerFactory.addErrorPages(new ErrorPage("/error"));
}@Bean // ⬅️TomcatServletWebServerFactory 初始化前用它增强, 注册所有 ErrorPageRegistrar
public ErrorPageRegistrarBeanPostProcessor errorPageRegistrarBeanPostProcessor() {return new ErrorPageRegistrarBeanPostProcessor();
}

收获💡

1. Tomcat 的错误页处理手段

演示2 - BasicErrorController

关键代码

@Bean // ⬅️ErrorProperties 封装环境键值, ErrorAttributes 控制有哪些错误信息
public BasicErrorController basicErrorController() {ErrorProperties errorProperties = new ErrorProperties();errorProperties.setIncludeException(true);return new BasicErrorController(new DefaultErrorAttributes(), errorProperties);
}@Bean // ⬅️名称为 error 的视图, 作为 BasicErrorController 的 text/html 响应结果
public View error() {return new View() {@Overridepublic void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {System.out.println(model);response.setContentType("text/html;charset=utf-8");response.getWriter().print("""<h3>服务器内部错误</h3>""");}};
}@Bean // ⬅️收集容器中所有 View 对象, bean 的名字作为视图名
public ViewResolver viewResolver() {return new BeanNameViewResolver();
}

收获💡

1. Spring Boot 中 BasicErrorController 如何工作

33) BeanNameUrlHandlerMapping 与 SimpleControllerHandlerAdapter

演示 - 本组映射器和适配器

关键代码

@Bean
public BeanNameUrlHandlerMapping beanNameUrlHandlerMapping() {return new BeanNameUrlHandlerMapping();
}@Bean
public SimpleControllerHandlerAdapter simpleControllerHandlerAdapter() {return new SimpleControllerHandlerAdapter();
}@Bean("/c3")
public Controller controller3() {return (request, response) -> {response.getWriter().print("this is c3");return null;};
}

收获💡

1. BeanNameUrlHandlerMapping，以 / 开头的 bean 的名字会被当作映射路径
2. 这些 bean 本身当作 handler，要求实现 Controller 接口
3. SimpleControllerHandlerAdapter，调用 handler
4. 模拟实现这组映射器和适配器

34) RouterFunctionMapping 与 HandlerFunctionAdapter

演示 - 本组映射器和适配器

关键代码

@Bean
public RouterFunctionMapping routerFunctionMapping() {return new RouterFunctionMapping();
}@Bean
public HandlerFunctionAdapter handlerFunctionAdapter() {return new HandlerFunctionAdapter();
}@Bean
public RouterFunction<ServerResponse> r1() {//           ⬇️映射条件   ⬇️handlerreturn route(GET("/r1"), request -> ok().body("this is r1"));
}

收获💡

1. RouterFunctionMapping, 通过 RequestPredicate 条件映射
2. handler 要实现 HandlerFunction 接口
3. HandlerFunctionAdapter, 调用 handler

35) SimpleUrlHandlerMapping 与 HttpRequestHandlerAdapter

演示1 - 本组映射器和适配器

代码参考

org.springframework.boot.autoconfigure.web.servlet.A35

关键代码

@Bean
public SimpleUrlHandlerMapping simpleUrlHandlerMapping(ApplicationContext context) {SimpleUrlHandlerMapping handlerMapping = new SimpleUrlHandlerMapping();Map<String, ResourceHttpRequestHandler> map = context.getBeansOfType(ResourceHttpRequestHandler.class);handlerMapping.setUrlMap(map);return handlerMapping;
}@Bean
public HttpRequestHandlerAdapter httpRequestHandlerAdapter() {return new HttpRequestHandlerAdapter();
}@Bean("/**")
public ResourceHttpRequestHandler handler1() {ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();handler.setLocations(List.of(new ClassPathResource("static/")));return handler;
}@Bean("/img/**")
public ResourceHttpRequestHandler handler2() {ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();handler.setLocations(List.of(new ClassPathResource("images/")));return handler;
}

收获💡

1. SimpleUrlHandlerMapping 不会在初始化时收集映射信息，需要手动收集
2. SimpleUrlHandlerMapping 映射路径
3. ResourceHttpRequestHandler 作为静态资源 handler
4. HttpRequestHandlerAdapter, 调用此 handler

演示2 - 静态资源解析优化

关键代码

@Bean("/**")
public ResourceHttpRequestHandler handler1() {ResourceHttpRequestHandler handler = new ResourceHttpRequestHandler();handler.setLocations(List.of(new ClassPathResource("static/")));handler.setResourceResolvers(List.of(// ⬇️缓存优化new CachingResourceResolver(new ConcurrentMapCache("cache1")),// ⬇️压缩优化new EncodedResourceResolver(),// ⬇️原始资源解析new PathResourceResolver()));return handler;
}

收获💡

1. 责任链模式体现
2. 压缩文件需要手动生成

演示3 - 欢迎页

关键代码

@Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext context) {Resource resource = context.getResource("classpath:static/index.html");return new WelcomePageHandlerMapping(null, context, resource, "/**");
}@Bean
public SimpleControllerHandlerAdapter simpleControllerHandlerAdapter() {return new SimpleControllerHandlerAdapter();
}

收获💡

1. 欢迎页支持静态欢迎页与动态欢迎页
2. WelcomePageHandlerMapping 映射欢迎页（即只映射 ‘/’）
   • 它内置的 handler ParameterizableViewController 作用是不执行逻辑，仅根据视图名找视图
   • 视图名固定为 forward:index.html
3. SimpleControllerHandlerAdapter, 调用 handler
   • 转发至 /index.html
   • 处理 /index.html 又会走上面的静态资源处理流程

映射器与适配器小结

1. HandlerMapping 负责建立请求与控制器之间的映射关系
   • RequestMappingHandlerMapping (与 @RequestMapping 匹配)
   • WelcomePageHandlerMapping (/)
   • BeanNameUrlHandlerMapping (与 bean 的名字匹配 以 / 开头)
   • RouterFunctionMapping (函数式 RequestPredicate, HandlerFunction)
   • SimpleUrlHandlerMapping (静态资源 通配符 /** /img/**)
   • 之间也会有顺序问题, boot 中默认顺序如上
2. HandlerAdapter 负责实现对各种各样的 handler 的适配调用
   • RequestMappingHandlerAdapter 处理：@RequestMapping 方法
     • 参数解析器、返回值处理器体现了组合模式
   • SimpleControllerHandlerAdapter 处理：Controller 接口
   • HandlerFunctionAdapter 处理：HandlerFunction 函数式接口
   • HttpRequestHandlerAdapter 处理：HttpRequestHandler 接口 (静态资源处理)
   • 这也是典型适配器模式体现

36) mvc 处理流程

当浏览器发送一个请求 http://localhost:8080/hello 后，请求到达服务器，其处理流程是：

1. 服务器提供了 DispatcherServlet，它使用的是标准 Servlet 技术

   • 路径：默认映射路径为 /，即会匹配到所有请求 URL，可作为请求的统一入口，也被称之为前控制器
     • jsp 不会匹配到 DispatcherServlet
     • 其它有路径的 Servlet 匹配优先级也高于 DispatcherServlet
   • 创建：在 Boot 中，由 DispatcherServletAutoConfiguration 这个自动配置类提供 DispatcherServlet 的 bean
   • 初始化：DispatcherServlet 初始化时会优先到容器里寻找各种组件，作为它的成员变量
     • HandlerMapping，初始化时记录映射关系
     • HandlerAdapter，初始化时准备参数解析器、返回值处理器、消息转换器
     • HandlerExceptionResolver，初始化时准备参数解析器、返回值处理器、消息转换器
     • ViewResolver

2. DispatcherServlet 会利用 RequestMappingHandlerMapping 查找控制器方法

   • 例如根据 /hello 路径找到 @RequestMapping(“/hello”) 对应的控制器方法

   • 控制器方法会被封装为 HandlerMethod 对象，并结合匹配到的拦截器一起返回给 DispatcherServlet

   • HandlerMethod 和拦截器合在一起称为 HandlerExecutionChain（调用链）对象

3. DispatcherServlet 接下来会：

   1. 调用拦截器的 preHandle 方法
   2. RequestMappingHandlerAdapter 调用 handle 方法，准备数据绑定工厂、模型工厂、ModelAndViewContainer、将 HandlerMethod 完善为 ServletInvocableHandlerMethod
      • @ControllerAdvice 全局增强点1️⃣：补充模型数据
      • @ControllerAdvice 全局增强点2️⃣：补充自定义类型转换器
      • 使用 HandlerMethodArgumentResolver 准备参数
        • @ControllerAdvice 全局增强点3️⃣：RequestBody 增强
      • 调用 ServletInvocableHandlerMethod
      • 使用 HandlerMethodReturnValueHandler 处理返回值
        • @ControllerAdvice 全局增强点4️⃣：ResponseBody 增强
      • 根据 ModelAndViewContainer 获取 ModelAndView
        • 如果返回的 ModelAndView 为 null，不走第 4 步视图解析及渲染流程
          • 例如，有的返回值处理器调用了 HttpMessageConverter 来将结果转换为 JSON，这时 ModelAndView 就为 null
        • 如果返回的 ModelAndView 不为 null，会在第 4 步走视图解析及渲染流程
   3. 调用拦截器的 postHandle 方法
   4. 处理异常或视图渲染
      • 如果 1~3 出现异常，走 ExceptionHandlerExceptionResolver 处理异常流程
        • @ControllerAdvice 全局增强点5️⃣：@ExceptionHandler 异常处理
      • 正常，走视图解析及渲染流程
   5. 调用拦截器的 afterCompletion 方法