前言
大部分的web开发者，开发的业务都是基于Http协议的：前端请求后端接口，携带参数，后端执行业务代码，再返回结果给前端。作者参与开发的项目，有一个报警推送的功能，服务端实时推送报警信息给浏览器端；还有像抖音里面，如果有人关注、回复你的评论时，抖音就会推送相关消息给你了，你就会收到一条消息。
有些同学会说了，基于Http协议也能实现啊：前端定时访问后端（每隔3s或者几秒），后端返回消息数据，前端拿到后弹出消息。这种方式太low了，而且每个浏览器都这样，使用系统的人一多，服务器的压力就太大了些。那到底用什么技术手段实现呢？我们的主角就登场了。
WebSocket是在单个TCP连接上进行全双工通信的应用层协议(Http协议也是应用层)，浏览器端和服务端都可主动发送数据给另一端。这样是不是比Http协议更适合消息推送这种场景。
浏览器端
作者建了一个SpringBoot项目，Html放在src\main\resources\static下：
<!DOCTYPE html>
<html lang="zh" xmlns:th="http://www.thymeleaf.org">
<head>
<!-- 解决中文乱码-->
<meta charset="UTF-8"/>
<title></title>
<script type="text/javascript" src="./js/jquery.min.js"></script>
</head>
<body>
<input id="input1" type="text" /><br/>
<input type="button" value="浏览器发送服务端" onclick="btnClick()" />
<input type="button" value="服务端发送浏览器" onclick="btnClick1()" />
<input type="button" value="重新打开连接" onclick="btnClick2()" />
<br/>
<textarea id="textArea" style="height: 50px"></textarea>
<script>
var ws;
webSocketInit();
function webSocketInit() {
ws =new WebSocket('ws://localhost:8080/bootdemo/webSocket/10086');
// 获取连接状态
console.log('ws连接状态[初始]：' + ws.readyState);
//监听是否连接成功
ws.onopen = function () {
console.log('ws连接状态[成功]：' + ws.readyState);
};
// 接听服务器发回的信息并处理展示
ws.onmessage = function (obj) {
console.log('接收到来自服务器的消息：');
var txt = $("#textArea").val();
$("#textArea").val(txt + "\n" + obj.data);
$("#textArea").scrollTop($("#textArea")[0].scrollHeight);
//完成通信后关闭WebSocket连接
// ws.close();
};
// 监听连接关闭事件
ws.onclose = function () {
// 监听整个过程中websocket的状态
console.log('ws连接状态[关闭]：' + ws.readyState);
};
// 监听并处理error事件
ws.onerror = function (error) {
console.log(error);
};
}
function btnClick() {
console.log("浏览器端发送消息：");
//连接成功则发送一个数据
ws.send($("#input1").val());
}
function btnClick1() {
$.ajax({
url: 'http://localhost:8080/bootdemo/pushWebSocket/publish?' +
'userId=10086&message=' + $("#input1").val(),
type: 'GET',
success: function (data) {
// console.log(data);
}
});
}
function btnClick2() {
webSocketInit();
}
</script>
</body>
</html>服务器端
先引入依赖：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-websocket</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<scope>provided</scope>
</dependency>
bean上添加@ServerEndpoint，作为WebSocket的服务端。
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.CopyOnWriteArraySet;
@Component
@Slf4j
@ServerEndpoint("/webSocket/{userId}")
public class WebSocketServer {
//与某个客户端的连接会话，需要通过它来给客户端发送数据
private Session session;
private static final CopyOnWriteArraySet<WebSocketServer> webSockets =
new CopyOnWriteArraySet<>();
// 用来存在线连接数
private static final Map<String, Session> sessionPool =
new HashMap<String, Session>();
@OnOpen
public void onOpen(Session session, @PathParam(value = "userId")
String userId) {
try {
this.session = session;
webSockets.add(this);
sessionPool.put(userId, session);
}
catch (Exception e) {
}
}
@OnMessage
public void onMessage(String message) {
log.info("websocket消息: 收到客户端消息:" + message);
}
public void sendOneMessage(String userId, String message) {
Session session = sessionPool.get(userId);
if (session != null && session.isOpen()) {
try {
log.info("服务端推送消息：" + message);
session.getAsyncRemote().sendText(message);
}
catch (Exception e) {
e.printStackTrace();
}
}
}
}
进行注册：
@Configuration
public class WebSocketConfigOne {
@Bean
public ServerEndpointExporter serverEndpointExporter() {
return new ServerEndpointExporter();
}
}
推送消息的控制器：
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import java.util.HashMap;
import java.util.Map;
@Controller
@RequestMapping("/pushWebSocket")
public class WebSocketController {
@Autowired
private WebSocketServer webSocketServer;
@GetMapping("/publish")
@ResponseBody
public Map publish(String userId, String message) {
webSocketServer.sendOneMessage(userId, message);
HashMap<String, Object> map = new HashMap<>();
map.put("code", 200);
return map;
}
}
还有我的配置文件application.properties：
# web port
server.port=8080
server.servlet.context-path=/bootdemo
运行启动类后，访问html(localhost:8080/bootdemo/index.html)如下：
有的同学一思索，点击图中的第2个按钮"服务端发送浏览器"，你这好像也是前端先请求，再推送的消息；我们的WebSocketController#publish方法，在真实的场景下，可以在后端的定时任务中、消息中间件的消费者端调用，不用前端先发送请求。
当然SpringBoot有专门构建WebSocket服务端的方式。
核心配置类：
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.http.server.ServletServerHttpRequest;
import org.springframework.web.servlet.HandlerMapping;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;
import org.springframework.web.socket.server.HandshakeInterceptor;
import javax.servlet.http.HttpServletRequest;
import java.util.Map;
@Configuration
@EnableWebSocket
@Slf4j
public class WebSocketConfig1 implements WebSocketConfigurer {
@Override
public void registerWebSocketHandlers(WebSocketHandlerRegistry
registry) {
registry.addHandler(new MyWebSocketHandler(), "/webSocket/{userId}")//设置连接路径和处理
.setAllowedOrigins("*")
.addInterceptors(new MyWebSocketInterceptor());//设置拦截器
}
class MyWebSocketInterceptor implements HandshakeInterceptor {
//前置拦截一般用来注册用户信息，绑定 WebSocketSession
@Override
public boolean beforeHandshake(ServerHttpRequest request,
ServerHttpResponse response, WebSocketHandler wsHandler,
Map<String, Object> attributes) throws Exception {
log.info("前置拦截~~");
if (!(request instanceof ServletServerHttpRequest)) {
return true;
}
HttpServletRequest servletRequest =
((ServletServerHttpRequest)request).getServletRequest();
Map map = (Map)servletRequest.getAttribute(HandlerMapping.
URI_TEMPLATE_VARIABLES_ATTRIBUTE);
String userId = (String)map.get("userId");
attributes.put("userId", userId);
return true;
}
@Override
public void afterHandshake(ServerHttpRequest request,
ServerHttpResponse response, WebSocketHandler wsHandler,
Exception exception) {
log.info("后置拦截~~");
}
}
}核心处理器：
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.*;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
@Slf4j
@Component
public class MyWebSocketHandler implements WebSocketHandler {
private static final Map<String, WebSocketSession> SESSIONS =
new ConcurrentHashMap<>();
@Override
public void afterConnectionEstablished(WebSocketSession session)
throws Exception {
String userId = (String) session.getAttributes().get("userId");
SESSIONS.put(userId, session);
}
@Override
public void handleMessage(WebSocketSession session,
WebSocketMessage<?> message) throws Exception {
String msg = message.getPayload().toString();
log.info("收到客户端消息：" + msg);
}
@Override
public void handleTransportError(WebSocketSession session,
Throwable exception) throws Exception {
log.info("连接出错");
if (session.isOpen()) {
session.close();
}
}
@Override
public void afterConnectionClosed(WebSocketSession session,
CloseStatus closeStatus) throws Exception {
log.info("连接关闭：status:" + closeStatus);
}
@Override
public boolean supportsPartialMessages() {
return false;
}
public void sendMessage(String userId, String message) {
WebSocketSession webSocketSession = SESSIONS.get(userId);
if (webSocketSession == null || !webSocketSession.isOpen()) {
return;
}
try {
webSocketSession.sendMessage(new TextMessage(message));
}
catch (Exception ex) {
log.error("推送消息异常：" + ex);
}
}
}控制器也改造下：
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import java.util.HashMap;
import java.util.Map;
@Controller
@RequestMapping("/pushWebSocket")
public class WebSocketController {
@Autowired
private MyWebSocketHandler handler;
@GetMapping("/publish")
@ResponseBody
public Map publish(String userId, String message) {
handler.sendMessage(userId, message);
HashMap<String, Object> map = new HashMap<>();
map.put("code", 200);
return map;
}
}
前端部分不用做修改，和之前一样的代码。
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