Spring WebSocket 404错误的解决方法

近来学习 spring websocket 时按照 Spring IN ACTioN 中示例编写代码，运行时浏览器报404 错误

WEBSocket connection to 'ws://localhost/websocket/marco' failed: Error during WebSocket handshake: Unexpected response code: 404

按照 Spring IN ACTION 中步骤：
首先，继承 AbstractWebSocketHandler，重载以下 3 个方法：
- handleTextMessage – 处理文本类型消息
- afterConnectionEstablished – 新连接建立后调用
- afterConnectionClosed – 连接关闭后调用

import org.springframework.web.socket.CloseStatus;import org.springframework.web.socket.TextMessage;import org.springframework.web.socket.WebSocketSession;import org.springframework.web.socket.handler.AbstractWebSocketHandler;public class MarcoHandler extends AbstractWebSocketHandler { protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {  System.out.println("Received message: " + message.getPayload());  Thread.sleep(2000);  session.sendMessage(new TextMessage("Polo!")); } @Override public void afterConnectionEstablished(WebSocketSession session) {  System.out.println("Connection established!"); } @Override public void afterConnectionClosed(WebSocketSession session, CloseStatus status) {  System.out.println("Connection closed. Status: " + status); }}