Spring 4.0的一个最大更新是增加了websocket的支持。websocket提供了一个在web应用中的高效、双向的通讯，需要考虑到客户端（浏览器）和服务器之间的高频和低延时消息交换。一般的应用场景有：在线交易、游戏、协作、数据可视化等。

使用websocket需要考虑的浏览器的支持（IE<10不支持），目前主流的浏览器都能很好的支持websocket。

websocket协议中有一些子协议，可以从更高的层次实现编程模型，就像我们使用HTTP而不是TCP一样。这些子协议有STOMP,WAMP等。

本教程只考虑websocket的简单实用，包含Spring对JSR-356的支持及Spring WebSocket API。

1、Java API for WebSocket(JSR-356)

Java API for WebSocket已经是Java EE 7的一部分。它定义了两类endpoit（都是EndPoint类的子类），使用注解标识@ClientEndpoint和@ServerEndpoint。

1.1 Servlet容器扫描初始化

通过Spring初始化一个endpoint，只需配置一个SpringConfigurator在类上的@ServerEndpoint注解上。

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package org.springframework.samples.websocket.config;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.samples.websocket.echo.DefaultEchoService;

import org.springframework.samples.websocket.echo.EchoEndpoint;

import org.springframework.samples.websocket.echo.EchoService;

import org.springframework.web.socket.server.standard.ServerEndpointExporter;

import org.springframework.web.socket.server.standard.ServerEndpointRegistration;

@Configuration

public class EndpointConfig {

    @Bean

    public ServerEndpointExporter endpointExporter() {

        return new ServerEndpointExporter();

    }

    @Bean

    public ServerEndpointRegistration echo() {

        return new ServerEndpointRegistration("/echo", EchoEndpoint.class);

    }

    @Bean

    public ServerEndpointRegistration echoSingleton() {

        return new ServerEndpointRegistration("/echoSingleton", new EchoEndpoint(echoService()));

    }

//    @Bean

//    public EchoAnnotatedEndpoint echoAnnotatedSingleton() {

//        return new EchoAnnotatedEndpoint(echoService());

//    }

    @Bean

    public EchoService echoService() {

        return new DefaultEchoService("Did you say \"%s\"?");

    }

}

上例假设SpringContextLoaderListener用来加载配置，这是个典型的web应用。Servlet容器将通过扫描@ServerEndpoint和SpringConfigurator初始化一个新的websocket会话。

1.2 Spring 初始化

如果你想使用一个单独的实例而不使用Servlet容器扫描，将EchoEndpoint类声明称一个bean，并增加一个ServerEndpointExporter的bean：

EchoEndpoint 可以通过EndPointRegistration发布

2、Spring WebSocket API

Spring WebSocket API提供了SockJS的支持，且有些容器如Jetty 9目前还没有对JSR-356的支持，所以有Spring WebSocket API是必要的。

Spring WebSocket API的核心接口是WebSocketHandler。下面是一个处理文本消息的handler的实现：

import org.springframework.web.socket.adapter.TextWebSocketHandlerAdapter;
public class EchoHandler extends TextWebSocketHandlerAdapter {
@Override
public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
session.sendMessage(message);
}
}

WebSocketHandler可以通过WebSocketHttpRequestHandler插入到Spring MVC里：

import org.springframework.web.socket.server.support.WebSocketHttpRequestHandler;
@Configuration
public class WebConfig {
@Bean
public SimpleUrlHandlerMapping handlerMapping() {
Map<String, Object> urlMap = new HashMap<String, Object>();
urlMap.put("/echo", new WebSocketHttpRequestHandler(new EchoHandler()));
SimpleUrlHandlerMapping hm = new SimpleUrlHandlerMapping();
hm.setUrlMap(urlMap);
return hm;
}
}

SockJS服务器端的支持

SockJs是一个脚本框架，它提供类似于websocket的编程模式但是可以适应不同的浏览器（包括不支持websocket的浏览器）。

开启SockJS的支持，声明一个SockJsService，和一个url映射，然后提供一个WebSocketHandler来处理消息。虽然我们是哟个SockJS我们开发的方式是一样的，但是随着浏览器的不同传输的协议可以是Http Streaming，long polling等。

import org.springframework.web.socket.sockjs.SockJsService;
// ...
@Configuration
public class WebConfig {
@Bean
public SimpleUrlHandlerMapping handlerMapping() {
SockJsService sockJsService = new DefaultSockJsService(taskScheduler());
Map<String, Object> urlMap = new HashMap<String, Object>();
urlMap.put("/echo/**", new SockJsHttpRequestHandler(sockJsService, new EchoHandler()));
SimpleUrlHandlerMapping hm = new SimpleUrlHandlerMapping();
hm.setUrlMap(urlMap);
return hm;
}
@Bean
public ThreadPoolTaskScheduler taskScheduler() {
ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
taskScheduler.setThreadNamePrefix("SockJS-");
return taskScheduler;
}
}

在我们实际使用中我们会使用WebSocketConfigurer集中注册WebSocket服务：

@Configuration
@EnableWebMvc
@EnableWebSocket//开启websocket
public class WebConfig extends WebMvcConfigurerAdapter implements WebSocketConfigurer {
@Override
public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
registry.addHandler(echoWebSocketHandler(), "/echo"); //提供符合W3C标准的Websocket数据
registry.addHandler(snakeWebSocketHandler(), "/snake");
registry.addHandler(echoWebSocketHandler(), "/sockjs/echo").withSockJS();//提供符合SockJS的数据
registry.addHandler(snakeWebSocketHandler(), "/sockjs/snake").withSockJS();
}
@Bean
public WebSocketHandler echoWebSocketHandler() {
return new EchoWebSocketHandler(echoService());
}
@Bean
public WebSocketHandler snakeWebSocketHandler() {
return new PerConnectionWebSocketHandler(SnakeWebSocketHandler.class);
}
@Bean
public DefaultEchoService echoService() {
return new DefaultEchoService("Did you say \"%s\"?");
}
// Allow serving HTML files through the default Servlet
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable();
}
}

SockJS客户端代码：

<script type="text/javascript">

        var ws = null;

        function setConnected(connected) {

            document.getElementById('connect').disabled = connected;

            document.getElementById('disconnect').disabled = !connected;

            document.getElementById('echo').disabled = !connected;

        }

        function connect() {

            var target = document.getElementById('target').value;

            if (target == '') {

                alert('Please select server side connection implementation.');

                return;

            }

            if ('WebSocket' in window) {

                ws = new WebSocket(target);

            } else if ('MozWebSocket' in window) {

                ws = new MozWebSocket(target);

            } else {

                alert('WebSocket is not supported by this browser.');

                return;

            }

            ws.onopen = function () {

                setConnected(true);

                log('Info: WebSocket connection opened.');

            };

            ws.onmessage = function (event) {

                log('Received: ' + event.data);

            };

            ws.onclose = function () {

                setConnected(false);

                log('Info: WebSocket connection closed.');

            };

        }

        function disconnect() {

            if (ws != null) {

                ws.close();

                ws = null;

            }

            setConnected(false);

        }

        function echo() {

            if (ws != null) {

                var message = document.getElementById('message').value;

                log('Sent: ' + message);

                ws.send(message);

            } else {

                alert('WebSocket connection not established, please connect.');

            }

        }

        function updateTarget(target) {

            if (window.location.protocol == 'http:') {

                document.getElementById('target').value = 'ws://' + window.location.host + target;

            } else {

                document.getElementById('target').value = 'wss://' + window.location.host + target;

            }

        }

        function log(message) {

            var console = document.getElementById('console');

            var p = document.createElement('p');

            p.style.wordWrap = 'break-word';

            p.appendChild(document.createTextNode(message));

            console.appendChild(p);

            while (console.childNodes.length > 25) {

                console.removeChild(console.firstChild);

            }

            console.scrollTop = console.scrollHeight;

        }

    </script>

ws://localhost:8080/spring-websocket-test/echo

ws://localhost:8080/spring-websocket-test/echoSingleton

ws://localhost:8080/spring-websocket-test/echoAnnotated

程序用maven打成war后用tomcat 8发布查看效果。

E:\myspace\spring-websocket-test-endpoint>mvn -DskipTests clean package

在target目录下生成了spring-websocket-test.war，部署到tomcat下，测试结果如下：

本例源码：spring-websocket-test-master.zip

巴特西

spring4.0之九：websocket简单应用