WebSocket实现长连接实时消息推送

WebSocket用于在Web浏览器和服务器之间进行任意的双向数据传输的一种技术。WebSocket协议基于
TCP协议实现，包含初始的握手过程，以及后续的多次数据帧双向传输过程。其目的是在WebSocket应用和
WebSocket服务器进行频繁双向通信时，可以使服务器避免打开多个HTTP连接进行工作来节约资源，提高 了工作效率和资源利用率。

1.POM文件添加依赖包

<dependency>
    <groupId>javax.websocket</groupId>
    <artifactId>javax.websocket-api</artifactId>
    <version>1.1</version>
    <scope>provided</scope>
 </dependency>

2.后台webSocket 服务端点工具类

package com.zyf.test.util;
 
import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import com.alibaba.fastjson.JSONObject;
import com.zyf.test.common.StringUtil;
 
 
@ServerEndpoint("/websocket/{username}")
public class WebSocketUtil {
    
    private static int onlineCount = 0;
    private static Map<String, WebSocketUtil> clients = new ConcurrentHashMap<String, WebSocketUtil>();
    private Session session;
    private String username;
    
    @OnOpen
    public void onOpen(@PathParam("username") String username, Session session) throws IOException {
        this.username = username;
        this.session = session;
        addOnlineCount();
        clients.put(username, this);
        System.out.println(username+"已连接，当前连接数："+getOnlineCount());
    }
 
    @OnClose
    public void onClose() throws IOException {
        clients.remove(username);
        subOnlineCount();
    }
    
    @OnMessage
    public void onMessage(String message) throws IOException {
        if(StringUtil.isNotEmpty(message)){
            JSONObject jsonTo = JSONObject.parseObject(message);
            if (!jsonTo.get("To").equals("All")) {
                sendMessageTo("给一个人", jsonTo.get("To").toString());
            } else {
                sendMessageAll("给所有人");
            }
        }
    }
    
    @OnError
    public void onError(Session session, Throwable error) {
        error.printStackTrace();
    }
    
    public void sendMessageTo(String message, String To) throws IOException {
        for (WebSocketUtil item : clients.values()) {
            String client = item.username.split("_")[0];
            if (client.equals(To)){
                item.session.getAsyncRemote().sendText(message);
                System.out.println("已给用户["+item.username+"]发送信息完毕！");
            }
        }
    }
    
    public void sendMessageAll(String message) throws IOException {
        for (WebSocketUtil item : clients.values()) {
            item.session.getAsyncRemote().sendText(message);
        }
    }
    
    public static synchronized int getOnlineCount() {
        return onlineCount;
    }
    
    public static synchronized void addOnlineCount() {
        WebSocketUtil.onlineCount++;
    }
    
    public static synchronized void subOnlineCount() {
        WebSocketUtil.onlineCount--;
    }
 
    public static synchronized Map<String, WebSocketUtil> getClients() {
        return clients;
    }
    
}

3.具体业务中应用，此处根据自身业务使用

//业务代码，例如：前台发起二维码扫码实名认证请求，需要后台认证完成后主动推送消息给前台修改二维码状态
WebSocketUtil webSocketUtil = new WebSocketUtil();
String message = "";//此处是传递给前台的数据，可以是json串，方便前端解析
String to="张三";//此参数为前端要接收信息的用户
try {
        webSocketUtil.sendMessageTo(message, to);
    } catch (IOException e) {
            e.printStackTrace();
        logger.error("给前台用户发送信息失败,异常：{}",e);
    }
//自己的业务处理代码

4.前端页面

var websocket = null;
//username 参数为客户端发起后台请求链接的用户
//初始链接之前二维码状态为未认证，
$("#verifyTs").html("未认证");
function verify(username) {
    var protocol = window.location.protocol;
    var webscoketProtocol="ws:";
    if("https:"==protocol){
        webscoketProtocol="wss:";
    }
    if('WebSocket' in window){
        var url = webscoketProtocol+'//' + window.location.host + projectName+'/websocket/'+username;
        websocket = new WebSocket(url);      //打开WebSocket
    }else{
        alert("你的浏览器不支持WebSocket");
    }
    //连接发生错误的回调方法  
    websocket.onerror = function() {  
        alert("WebSocket连接发生错误，请稍后再试！");
        console.log(username+"WebSocket连接发生错误，请稍后再试！");
    };
    websocket.onopen = function() {
        console.log(username+"WebSocket连接成功");
//        sock.send(JSON.stringify());//客户端发送消息
    };
    websocket.onmessage = function(e) {//接收消息
        e = e || event;
        var message = e.data;
        console.log(username+"接收到消息:"+message);
        //根据不同状态操作二维码
        if(message!=null){
            var verifyData=JSON.parse(message);
            if(verifyData!=null){
                var status=verifyData.statusCode;
                if(status==1){
                    $("#verifyTs").html("认证通过");
                    $("#srrzQrCodeDiv").attr("style","display:none;");
                    applyFallBack();
                }else if(status==2){
                    $("#verifyTs").html("认证未通过,原因:"+verifyData.auditConclusions);
                }else if(status==0){
                    $("#verifyTs").html("认证中");
                }else{
                    $("#verifyTs").html("未认证");
                }
            }
        }
    };
    websocket.onclose = function() {         //处理连接关闭事件
        console.log(username+"WebSocket连接关闭");
    };
    window.onbeforeunload = function() {  
         websocket.close();
    };
}