学习WebSocket(二):使用Spring WebSocket做一个简单聊天室

　　聊天室高频率、低延时完全符合websocket的特点，所以聊天室使用websocket再适合不过了。

　　聊天室的功能并没有比上一节代码多多少，主要在握手阶段对用户的session做处理，对用户的消息进行分发和处理。

　　握手阶段HandshakeInterceptor需要做的处理　　

public class HandshakeInterceptor extends HttpSessionHandshakeInterceptor {
　　.........
    @Override
    public boolean beforeHandshake(ServerHttpRequest request, ServerHttpResponse response, WebSocketHandler wsHandler, Map<String, Object> attributes)throws Exception {
        System.out.println("Before Handshake");
        if (request instanceof ServletServerHttpRequest) {
            ServletServerHttpRequest servletRequest = (ServletServerHttpRequest) request;
            HttpSession session = servletRequest.getServletRequest().getSession(false);
            String username = (String) session.getAttribute("username");
            if(username != null && "".equals(""))
                attributes.put("username", username);
        }
        return super.beforeHandshake(request, response, wsHandler, attributes);
    }

　　MessageHandler需要对消息进行分发

public class MessageHandler extends TextWebSocketHandler {
    //保存用户的websocket连接
    private Map<String,WebSocketSession> users = new HashMap<String,WebSocketSession>();
    
    protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
        if(!"".equals(message.getPayload()))
            session.sendMessage(message);
        
    }
    
    public void afterConnectionEstablished(WebSocketSession session)throws Exception {
　　　　 //连接建立后，保存用户信息，并向全部在线用户发登陆信息
        users.put(session.getId(), session);
        String username = (String) session.getAttributes().get("username");
        if(users != null){
            for(WebSocketSession wssession : users.values()){
                handleMessage(wssession, new TextMessage(username + " joined!!"));
            }
        }
    }
    @Override
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
        //退出后，需要移除用户信息
        users.remove(session.getId());
        String username = (String) session.getAttributes().get("username");
        if(users != null){
            for(WebSocketSession wssession : users.values()){
                handleMessage(wssession, new TextMessage(username + " left!!"));
            }
        }
    }
    //群发信息
    public void sendMsgToUsers(TextMessage message) throws Exception{
        if(users != null){
            for(WebSocketSession wssession : users.values()){
                handleMessage(wssession, message);
            }
        }
    }
    
    
}