websocket 简要介绍+代码（服务端代码）

websocket  是 全双工网络通信协议

一次握手，持久通信，可以由服务端发往客户端

【http协议，只能客户端发送请求，轮询刷新，频繁创建连接】

下面来看一下代码如何实现

服务端的实现

一，编程式  继承javax.websocket.Endpoint  实现它的方法

二，注解式   定义一个pojo类，添加@ServerEndpoint相关注解

代码采用注解式来实现

package com.websocket;

import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import org.apache.commons.lang3.StringUtils;
import org.springframework.stereotype.Component;
import cn.hutool.log.Log;
import cn.hutool.log.LogFactory;



@ServerEndpoint("/imserver/{userId}")
@Component
public class WebSocketServer {

    static Log log=LogFactory.get(WebSocketServer.class);
    
    private static int onlineCount = 0;
    
    private static ConcurrentHashMap webSocketMap = new ConcurrentHashMap<>();
    
    private Session session;
    
    private String userId="";

    
    @onOpen
    public void onOpen(Session session,@PathParam("userId") String userId) {
        this.session = session;
        this.userId=userId;
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);
            webSocketMap.put(userId,this);
            //加入set中
        }else{
            webSocketMap.put(userId,this);
            //加入set中
            addonlineCount();
            //在线数加1
        }

        log.info("用户连接:"+userId+",当前在线人数为:" + getonlineCount());

        try {
            sendMessage("连接成功");
        } catch (IOException e) {
            log.error("用户:"+userId+",网络异常!!!!!!");
        }
    }

    
    @onClose
    public void onClose() {
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);
            //从set中删除
            subonlineCount();
        }
        log.info("用户退出:"+userId+",当前在线人数为:" + getonlineCount());
    }

    
    @onMessage
    public void onMessage(String message, Session session) {
        log.info("用户消息:"+userId+",报文:"+message);
        //可以群发消息
        //消息保存到数据库、redis
        if(StringUtils.isNotBlank(message)){
            try {
                //解析发送的报文
                JSonObject jsonObject = JSON.parseObject(message);
                //追加发送人(防止串改)
                jsonObject.put("fromUserId",this.userId);
                String toUserId=jsonObject.getString("toUserId");
                //传送给对应toUserId用户的websocket
                if(StringUtils.isNotBlank(toUserId)&&webSocketMap.containsKey(toUserId)){
                    webSocketMap.get(toUserId).sendMessage(jsonObject.toJSonString());
                }else{
                    log.error("请求的userId:"+toUserId+"不在该服务器上");
                    //否则不在这个服务器上，发送到mysql或者redis
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    
    @onError
    public void onError(Session session, Throwable error) {
        log.error("用户错误:"+this.userId+",原因:"+error.getMessage());
        error.printStackTrace();
    }
    
    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }


    
    public static void sendInfo(String message,@PathParam("userId") String userId) throws IOException {
        log.info("发送消息到:"+userId+"，报文:"+message);
        if(StringUtils.isNotBlank(userId)&&webSocketMap.containsKey(userId)){
            webSocketMap.get(userId).sendMessage(message);
        }else{
            log.error("用户"+userId+",不在线！");
        }
    }

    public static synchronized int getonlineCount() {
        return onlineCount;
    }

    public static synchronized void addonlineCount() {
        WebSocketServer.onlineCount++;
    }

    public static synchronized void subonlineCount() {
        WebSocketServer.onlineCount--;
    }
}

websocket的启动类

package com.websocket;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;


@Configuration
public class WebSocketConfig {

    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }

}