websocker无法注入依赖

在公司中准备用websocker统计在线人数，在WebSocketServer使用StringRedisTemplate保存数据到redis中去，但是在保存的时候显示

 StringRedisTemplate变量为null

  详细问题 

2023-08-20 10:37:14.109 ERROR 28240 --- [nio-7125-exec-1] o.a.t.websocket.pojo.PojoEndpointBase    : Failed to call onClose method of POJO end point for POJO of type [com.example.pipayshopapi.component.WebSocketServer]java.lang.reflect.InvocationTargetException: nullat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_382]at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_382]at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_382]at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_382]at org.apache.tomcat.websocket.pojo.PojoEndpointBase.onClose(PojoEndpointBase.java:103) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.WsSession.fireEndpointOnClose(WsSession.java:556) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.WsSession.doClose(WsSession.java:502) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.WsSession.doClose(WsSession.java:460) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.WsSession.close(WsSession.java:447) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.WsSession.close(WsSession.java:441) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.pojo.PojoEndpointBase.handleOnOpenOrCloseError(PojoEndpointBase.java:92) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.pojo.PojoEndpointBase.doOnOpen(PojoEndpointBase.java:77) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.pojo.PojoEndpointServer.onOpen(PojoEndpointServer.java:64) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:135) [tomcat-embed-websocket-9.0.41.jar:9.0.41]at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:935) [tomcat-embed-core-9.0.41.jar:9.0.41]at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597) [tomcat-embed-core-9.0.41.jar:9.0.41]at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.41.jar:9.0.41]at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_382]at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_382]at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.41.jar:9.0.41]at java.lang.Thread.run(Thread.java:750) [na:1.8.0_382]
Caused by: java.lang.NullPointerException: nullat com.example.pipayshopapi.component.WebSocketServer.onClose(WebSocketServer.java:70) ~[classes/:na]... 21 common frames omitted2023-08-20 10:37:14.109 ERROR 28240 --- [nio-7125-exec-1] c.e.p.component.WebSocketServer          : 发生错误
java.lang.NullPointerExceptionat com.example.pipayshopapi.component.WebSocketServer.onOpen(WebSocketServer.java:56)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at org.apache.tomcat.websocket.pojo.PojoEndpointBase.doOnOpen(PojoEndpointBase.java:65)at org.apache.tomcat.websocket.pojo.PojoEndpointServer.onOpen(PojoEndpointServer.java:64)at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:135)at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:935)at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Thread.java:750)
java.lang.reflect.InvocationTargetExceptionat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at org.apache.tomcat.websocket.pojo.PojoEndpointBase.onClose(PojoEndpointBase.java:103)at org.apache.tomcat.websocket.WsSession.fireEndpointOnClose(WsSession.java:556)at org.apache.tomcat.websocket.WsSession.doClose(WsSession.java:502)at org.apache.tomcat.websocket.WsSession.doClose(WsSession.java:460)at org.apache.tomcat.websocket.WsSession.close(WsSession.java:447)at org.apache.tomcat.websocket.WsSession.close(WsSession.java:441)at org.apache.tomcat.websocket.pojo.PojoEndpointBase.handleOnOpenOrCloseError(PojoEndpointBase.java:92)at org.apache.tomcat.websocket.pojo.PojoEndpointBase.doOnOpen(PojoEndpointBase.java:77)at org.apache.tomcat.websocket.pojo.PojoEndpointServer.onOpen(PojoEndpointServer.java:64)at org.apache.tomcat.websocket.server.WsHttpUpgradeHandler.init(WsHttpUpgradeHandler.java:135)at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:935)at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1597)at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Thread.java:750)
Caused by: java.lang.NullPointerExceptionat com.example.pipayshopapi.component.WebSocketServer.onClose(WebSocketServer.java:70)... 21 more

最后在网上搜索之后得出答案：

因为spring对象的创建都是以单例模式创建的，但是每一个用户连接websocker，都会创建一次webscket对象，所以当你启动项目时，你想要注入的对象已经注入进去，但是当用户连接是，新创建的websocket对象没有你要注入的对象，所以会报NullPointerException。

总结：spring管理的都是单例（singleton），和 websocket （多对象）相冲突.
解决方法：

在WebSocketServer中，使用set方法传入上下文

 private static StringRedisTemplate stringRedisTemplate;@Autowiredpublic void setChatService(StringRedisTemplate stringRedisTemplate) {WebSocketServer.stringRedisTemplate = stringRedisTemplate;}

 完整代码

import com.example.pipayshopapi.service.UserInfoService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Component;import javax.annotation.Resource;
import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;/*** @author websocket服务*/@Component
@ServerEndpoint(value = "/dailyActive/{userId}")
public class WebSocketServer {private static final Logger log = LoggerFactory.getLogger(WebSocketServer.class);// 注入查看聊天列表的服务/*** 记录当前在线连接数*/public static final Map<String, Session> dailyActiveCount = new ConcurrentHashMap<>();public static final String dailyActiveName="dailyActiveName";private RedisHandler redisHandler=RedisHandler.getInstance();private static StringRedisTemplate stringRedisTemplate;@Autowiredpublic void setChatService(StringRedisTemplate stringRedisTemplate) {WebSocketServer.stringRedisTemplate = stringRedisTemplate;}/*** 连接建立成功调用的方法*/@OnOpenpublic void onOpen(Session session, @PathParam("userId") String userId) {log.error(userId+"----------------------------------------------进入");// 保存当前用户sessiondailyActiveCount.put(userId, session);// 存入redis中去
//        redisHandler.savedailyActive(dailyActiveName,dailyActiveCount.size());stringRedisTemplate.opsForValue().set(dailyActiveName,String.valueOf(dailyActiveCount.size()));}/*** 连接关闭调用的方法*/@OnClosepublic void onClose(Session session, @PathParam("userId") String userId) {log.error(userId+"----------------------------------------------关闭");// 移除当前用户sessiondailyActiveCount.remove(userId);// 存入redis中去
//        redisHandler.savedailyActive(dailyActiveName,dailyActiveCount.size());stringRedisTemplate.opsForValue().set(dailyActiveName,String.valueOf(dailyActiveCount.size()));}/*** 收到客户端消息后调用的方法* 后台收到客户端发送过来的消息* onMessage 是一个消息的中转站* 接受 浏览器端 socket.send 发送过来的 json数据*/@OnMessagepublic void onMessage(Session session, String message,@PathParam("userId") String userId) {}@OnErrorpublic void onError(Session session, Throwable error) {log.error("发生错误");error.printStackTrace();}}