Jackson

first you need to add dependence:
gradle:

implementation 'com.fasterxml.jackson.core:jackson-databind:2.13.1'
implementation 'com.fasterxml.jackson.datatype:jackson-datatype-jsr310:2.13.1'

原生Jackson的使用示例:

/*** 原生Jackson的使用示例*/
public class JacksonUsageDemo {public static void main(String[] args) throws JsonProcessingException {Address address1 = new Address("北京", "王府井12号", true);Address address2 = new Address("成都", "天府大道55号", false);Person person = new Person("张三", 18, Gender.MALE, Arrays.asList(address1, address2));ObjectMapper objectMapper = new ObjectMapper();String json = objectMapper.writeValueAsString(person);System.out.println(json);Person result = objectMapper.readValue(json, Person.class);System.out.println(result);}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Person {private String name;private Integer age;private Gender gender;private List<Address> addressList;}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Address {private String city;private String detail;private Boolean isPrimary;}private enum Gender {MALE, FEMALE;}
}

if JSON and JavaBean are not same

场景一：JSON比JavaBean多字段，在反序列化时忽略未知字段

使用@JsonIgnoreProperties：可以忽略指定字段，也可以忽略本类所有未知字段

• @JsonIgnoreProperties(value = “year”):ignore the value of json
• @JsonIgnoreProperties(ignoreUnknown = true):ignore every unknown value of JSON

  @Data@NoArgsConstructor@AllArgsConstructor@JsonIgnoreProperties(value = "year")
//  @JsonIgnoreProperties(ignoreUnknown = true)private static class Car {private String color;private String type;}

场景二：需要的JSON比JavaBean少字段，在序列化时忽略多余字段

• 用@JsonIgnore在字段级别忽略
• 用@JsonIgnoreType在类级别忽略

@RestController
public class FieldsLessController {@GetMapping("/teachers/{id}")public Teacher getStudentById(@PathVariable("id") String id) {return new Teacher(id, "刘老师", Gender.FEMALE);}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Teacher {private String id;private String name;@JsonIgnoreprivate Gender gender;}//  @JsonIgnoreTypeprivate enum Gender {MALE, FEMALE;}
}

场景三：字段名不一致，在序列化和反序列化时改变字段名

• 使用@JsonProperty

@RestController
public class FieldsNameMismatchController {@GetMapping("/articles/{id}")public Article getStudentById(@PathVariable("id") String id) {return new Article(id, "论持久战");}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Article {@JsonProperty("articleId")private String id;@JsonProperty("articleTitle")private String title;}
}

json将会返回articleI&&articleTitle

场景四：结构不一致，在序列化时将对象拍平

• 使用@JsonUnwrapped

拍平后：
{
“id”: “1”,
“firstName”: “John”,
“lastName”: “Doe”
}

@RestController
@Slf4j
public class StructureMismatchController {@PostMapping("/employees")public void createEmployee(@RequestBody Employee employee) {log.info("create employee: {}", employee);}@GetMapping("/employees/{id}")public Employee getStudentById(@PathVariable("id") String id) {return new Employee(id, new Name("John", "Doe"));}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Employee {private String id;@JsonUnwrappedprivate Name name;}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Name {private String firstName;private String lastName;}
}

场景五：JSON中的枚举是数字形式，在序列化时使用枚举的序数值

• 使用@JsonValue

@RestController
public class EnumOrdinalController {@GetMapping("/users/v1/{id}")public User getUserById(@PathVariable String id) {return new User(id, "小红", Gender.FEMALE);}@Data@NoArgsConstructor@AllArgsConstructorprivate static class User {private String id;private String name;private Gender gender;}private static enum Gender {MALE, FEMALE;@JsonValuepublic int getOrdinal() {return ordinal();}}
}

场景六：JSON中的时间是特定格式，在序列化时指定时间格式

• 使用@JsonFormat

@RestController
public class TimeFormatController {@GetMapping("/events/{id}")public Event getEvent(@PathVariable("id") String id) {return new Event(id, "pay", new Date());}@Data@NoArgsConstructor@AllArgsConstructorprivate static class Event {private String id;private String name;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")private Date time;}
} 

使用自定义序列化器，枚举序列化成数字

@JsonSerialize(using = GenderSerializer.class)

@RestController
public class CustomSerializationController {@GetMapping("/users/v2/{id}")public User getUserById(@PathVariable String id) {return new User(id, "小红", Gender.FEMALE);}@Data@NoArgsConstructor@AllArgsConstructorprivate static class User {private String id;private String name;@JsonSerialize(using = GenderSerializer.class)private Gender gender;}private static enum Gender {MALE, FEMALE;}private static class GenderSerializer extends StdSerializer<Gender> {protected GenderSerializer() {super(Gender.class);}@Overridepublic void serialize(Gender value, JsonGenerator gen, SerializerProvider provider)throws IOException {gen.writeNumber(value.ordinal());}}
}