webscoket服务端向客户端发送消息

package org.meal.controller;

import java.io.IOException;
import java.util.concurrent.CopyOnWriteArraySet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint("/websockets")
public class WebscoketsController extends HttpServlet{
	//concurrent包的线程安全Set，用来存放每个客户端对应的MyWebSocket对象。若要实现服务端与单一客户端通信的话，可以使用Map来存放，其中Key可以为用户标识
    private static CopyOnWriteArraySet<WebscoketsController> webSocketSet = new CopyOnWriteArraySet<WebscoketsController>();
    //这个session不是Httpsession，相当于用户的唯一标识，用它进行与指定用户通讯
    private  javax.websocket.Session session=null;

    public void doGet(HttpServletRequest request, HttpServletResponse response,long deskId,long shopid) throws ServletException,IOException {
            //发送更新信号
            sendMessage(deskId,shopid);
           
        //response.sendRedirect("http://localhost:8080/order_meal/checkstand/index.jsp");
    }
    public void doPost(HttpServletRequest request,HttpServletResponse reponse) throws ServletException, IOException {
        doGet(request,reponse);
    }

   

    /**
     * @OnOpen allows us to intercept the creation of a new session.
     * The session class allows us to send data to the user.
     * In the method onOpen, we'll let the user know that the handshake was
     * successful.
     * 建立websocket连接时调用
     */
    @OnOpen
    public void onOpen(Session session){
        System.out.println("Session " + session.getId() + " has opened a connection");
        try {
            this.session=session;
            webSocketSet.add(this);     //加入set中
            session.getBasicRemote().sendText("Connection Established");
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    /**
     * When a user sends a message to the server, this method will intercept the message
     * and allow us to react to it. For now the message is read as a String.
     * 接收到客户端消息时使用，这个例子里没用
     */
    @OnMessage
    public void onMessage(String message, Session session){
        System.out.println("Message from " + session.getId() + ": " + message);
    }

    /**
     * The user closes the connection.
     *
     * Note: you can't send messages to the client from this method
     * 关闭连接时调用
     */
    @OnClose
    public void onClose(Session session){
        webSocketSet.remove(this);  //从set中删除
        System.out.println("Session " +session.getId()+" has closed!");
    }

    /**
     * 注意: OnError() 只能出现一次.   其中的参数都是可选的。
     * @param session
     * @param t
     */
    @OnError
    public void onError(Session session, Throwable t) {
        t.printStackTrace();
    }

    /**
     * 这个方法与上面几个方法不一样。没有用注解，是根据自己需要添加的方法。
     * @throws IOException
     * 发送自定义信号，“1”表示告诉前台，数据库发生改变了，需要刷新
     */
    public void sendMessage(long deskId,long shopid) throws IOException{
    	String id=String.valueOf(deskId);
    	String shop=String.valueOf(shopid);
    	String ids=id+","+shop;
        //群发消息
        for(WebscoketsController item: webSocketSet){
            try {
                item.session.getBasicRemote().sendText(ids);
            } catch (IOException e) {
                e.printStackTrace();
                continue;
            }
        }

    }
}


//在传送消息时，需要调用webscoket的doget函数
WebscoketsController controller2 = new WebscoketsController();
	try {
		controller2.doGet(request, response, list.get(list.size()-1).getDeskId(), shopId);
	} catch (ServletException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			} catch (IOException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
				}
jsp页面
 var websocket = null;
      //判断当前浏览器是否支持WebSocket
      if ('WebSocket' in window) {
    //建立连接，这里的/websocket ，是ManagerServlet中开头注解中的那个值
          websocket = new WebSocket("ws://115.158.20.211:8080/order_meal/websockets");
      }
      else {
          alert('当前浏览器 Not support websocket')
      }
      //连接发生错误的回调方法
      websocket.onerror = function () {
          setMessageInnerHTML("WebSocket连接发生错误");
      };
      //连接成功建立的回调方法
      websocket.onopen = function () {
          setMessageInnerHTML("WebSocket连接成功");
      }
      //接收到消息的回调方法
      websocket.onmessage = function (event) {
          setMessageInnerHTML(event.data);
          if(event.data=="1"){
              location.reload();
          }
      }
      //连接关闭的回调方法
      websocket.onclose = function () {
          setMessageInnerHTML("WebSocket连接关闭");
      }
      //监听窗口关闭事件，当窗口关闭时，主动去关闭websocket连接，防止连接还没断开就关闭窗口，server端会抛异常。
      window.onbeforeunload = function () {
          closeWebSocket();
      }
      //将消息显示在网页上
      function setMessageInnerHTML(innerHTML) {
    	  var ids=innerHTML.split(",");
    	  var deskId;
    	  var shopId;
    	  var shop="${admin.shopId}";
    	  console.log(shop)
    	  for(var i=0;i<ids.length;i++){
    		  	deskId=ids[i];
    		  	shopId=ids[i+1];
    		  	break;
    	}
    	  if(shop==shopId){
    		  $('#imgdiv').append(' <img alt="" src="images/message.png" class="imgclass" id="message">');
    		  var msg = "测试语音播放";
              var re = /^[0-9]+.?[0-9]*$/;
             
              if (re.test(innerHTML)){
            	  var str=deskId+'号餐桌已结账';
            	  voiceAnnouncements(str);
              }
              console.log(innerHTML);
    	  }
         
          
      }
      //关闭WebSocket连接
      function closeWebSocket() {
          websocket.close();
      }
      function voiceAnnouncements(str){
    	    //百度
    	    var url = "http://tts.baidu.com/text2audio?lan=zh&ie=UTF-8&text=" + encodeURI(str);        // baidu
    	    var n = new Audio(url);
    	    n.src = url;
    	    n.play();
    	}
	</script> 
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转载于:https://juejin.im/post/5c2d6f836fb9a049ff4e3d8f