/*
 *   這部分js將websocket封裝起來
 */
  var websocket = null;
  //判斷當前瀏覽器是否支持WebSocket
  if ('WebSocket' in window) {
    websocket = new WebSocket("ws://localhost:8080/GoodMan/ChatService");
  }
  else {
    alert('當前瀏覽器 Not support websocket')
  }
  
   //連接成功建立的回調(diào)方法
  websocket.onopen = function () {
    alert("WebSocket連接成功");
  }

  //連接發(fā)生錯誤的回調(diào)方法
  websocket.onerror = function () {
    alert("WebSocket連接發(fā)生錯誤");
  };
  
   //發(fā)送消息
  function sendMess(content) {
     var json ="{'username':'"+'${sessionScope.username }'+"', 'content':'"+content+"'}";
    websocket.send(json);
  }

  //接收到消息的回調(diào)方法
  websocket.onmessage = function (event) {
    var jsonString = event.data;    //接收到的信息存放在event.data中
    var data = JSON.parse(jsonString);  //將json字符串轉(zhuǎn)換成js對象
    // 然后輸出data
  }

   //連接關(guān)閉的回調(diào)方法
  websocket.onclose = function () {
    alert("WebSocket連接關(guān)閉");
  }

  //監(jiān)聽窗口關(guān)閉事件，當窗口關(guān)閉時，主動去關(guān)閉websocket連接，防止連接還沒斷開就關(guān)閉窗口，server端會拋異常。
  window.onbeforeunload = function () {
    closeWebSocket();
  }

  //關(guān)閉WebSocket連接
  function closeWebSocket() {
    websocket.close();
  }

import java.io.IOException;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import com.google.gson.Gson;

class Mess{    //封裝一條消息
  private String username;
  private String content;
  private String date;
  public Mess(String username, String content, String date) {
    super();
    this.username = username;
    this.content = content;
    this.date = date;
  }
  public String getUsername() {
    return username;
  }
  public void setUsername(String username) {
    this.username = username;
  }
  public String getContent() {
    return content;
  }
  public void setContent(String content) {
    this.content = content;
  }
  public String getDate() {
    return date;
  }
  public void setDate(String date) {
    this.date = date;
  }
}

@ServerEndpoint("/ChatService")
public class ChatService {      //每進入一個用戶，就新建一個ChatService對象
  
  private static int onlineCount = 0; //靜態(tài)變量， 用來記錄當前在線連接數(shù)
  private static Set webSocketSet = new HashSet<>();    //靜態(tài)變量，用來存放在線用戶
  private Session session;   //用于存儲與該用戶的會話，要通過它來給客戶端發(fā)送數(shù)據(jù)

  /**
   * 連接建立成功調(diào)用的方法
   * @param session 可選的參數(shù)。session為與某個客戶端的連接會話，需要通過它來給客戶端發(fā)送數(shù)據(jù)
   */
  @OnOpen
  public void onOpen(Session session){
    this.session = session;
    webSocketSet.add(this);   //加入set中
    addOnlineCount();      //在線數(shù)加1
    System.out.println("有新連接加入！當前在線人數(shù)為" + getOnlineCount());
  }
  
  /**
   * 連接關(guān)閉調(diào)用的方法
   */
  @OnClose
  public void onClose(){
    webSocketSet.remove(this); //從set中刪除
    subOnlineCount();      //在線數(shù)減1
    System.out.println("有一連接關(guān)閉！當前在線人數(shù)為" + getOnlineCount());
  }

  /**
   * 收到客戶端消息后調(diào)用的方法
   * @param message 客戶端發(fā)送過來的消息
   * @param session 可選的參數(shù)
   */
  @OnMessage
  public void onMessage(String data, Session session) {
    Mess mess = new Gson().fromJson(data, Mess.class);
    System.out.printf("來%s的消息:%s\n", mess.getUsername(), mess.getContent());
    //群發(fā)消息
    for(ChatService item: webSocketSet){
      try {
        item.sendMessage(mess);
      } catch (IOException e) {
        e.printStackTrace();
        continue;
      }
    }
  }
  
  /**
   * 發(fā)生錯誤時調(diào)用
   * @param session
   * @param error
   */
  @OnError
  public void onError(Session session, Throwable error){
    System.out.println("發(fā)生錯誤");
    error.printStackTrace();
  }

  //以下為輔助函數(shù)
  public void sendMessage(Mess mess) throws IOException{

    String datatime = new java.text.SimpleDateFormat("yyyy-MM-dd hh:mm:ss").format(new Date());
    mess.setDate(datatime);
    String jsonInfo = new Gson().toJson(mess);    //將消息對象轉(zhuǎn)換成json字符串
    this.session.getAsyncRemote().sendText(jsonInfo); //通過session異步地將信息發(fā)送到客戶端上
  }

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

  public static synchronized void addOnlineCount() {
    ChatService.onlineCount++;
  }

  public static synchronized void subOnlineCount() {
    ChatService.onlineCount--;
  }
}