一:概述
作为HTML5新特性之一的WebSocket组件,在实时性有一定要求的WEB应用开发中还是有一定用武之地,高版本的IE、Chrome、FF浏览器都支持Websocket,标准的Websocket通信是基于RFC6455实现服务器端与客户端握手与消息接发的。如果对Websocket通信不是太理解,可以查看RFC文档即可,简单说就是通过发送HTTP请求,实现双方握手,将无状态的HTTP通信协议进一步升级成有状态的通信协议,同时Websocket还支持子协议选项与安全传输。标准的websocket连接URL以ws开头,如果是基于TLS的则以wss开头。基于Websocket可以很方便的开发基于web聊天程序,各种网页消息通知与推送通知。
如果非要扒一扒websocket的今生前世的话,还记得最早的基于HTTP轮询实现网页即时通信的方式,那种做法比较消耗资源、于是有人改进了编程CometD长连接方式,可是本质上还是换汤不换药,而websocket的出现正好解决了这些问题,但是很多浏览器的低版本还是不支持websocket,于是还催生了一些基于websocket理念实现的JS通信框架,其中学得比较像的有SockJS与socket.io,他们都号称支持websocket,然后如果浏览器端不支持原生的websocket,它们会自动启用fallback选项使用其它诸如ajax、Http轮询、长轮询/连接、甚至是flash的socket等机制实现模拟websocket的工作方式,但是他们最大的弊端是如果客户端使用了这些框架,服务器必须用它们,否则等待开发者就是一大堆无法回避的问题,同时很多都是无解的。主要原因在于它们实现自己的协议集,不照它们的格式处理数据没法玩。闲话说的有点多。
二 : 实现步骤
Tomcat7的高版本中实现了websocket服务器端RFC6455标准协议,可以跟浏览器端websocket进行通信,首先要做好如下几步:
1. 安装高版本JDK – JDK8
2. 安装tomcat 7.0.64
3. 在eclipse中建立一个动态的web项目
根据JSR标准,Java中实现websocket的标准接口可以基于注解方式,tomcat也搞好了,只有我们实现如下代码,即可创建一个websocket回声服务器:
package com.websocket.demo; import java.io.IOException; import java.nio.ByteBuffer; import javax.websocket.OnMessage; import javax.websocket.OnOpen; import javax.websocket.Session; import javax.websocket.server.ServerEndpoint; @ServerEndpoint(value = "/echo") public class EchoExample { @OnMessage public void echoTextMessage(Session session, String msg, boolean last) { try { if (session.isOpen()) { System.out.println("received from client message = " + msg); session.getBasicRemote().sendText(msg, last); } } catch (IOException e) { try { session.close(); } catch (IOException e1) { } } } @OnOpen public void openConn(Session session) throws IOException { session.getBasicRemote().sendText("hello web socket"); // means open it } @OnMessage public void echoBinaryMessage(Session session, ByteBuffer bb, boolean last) { System.out.println("send binary message..."); try { if (session.isOpen()) { System.out.println("byte buffer lenghth : " + bb.array().length); System.out.println("byte buffer content: " + ((bb.array()[0]) & 0xff)); System.out.println("byte buffer content: " + ((bb.array()[1]) & 0xff)); System.out.println("byte buffer content: " + ((bb.array()[2]) & 0xff)); session.getBasicRemote().sendBinary(bb, last); } } catch (IOException e) { try { session.close(); } catch (IOException e1) { // Ignore } } } }
如何在tomcat中启动websocket服务器,首先需要在web.xml添加如下配置:
<listener> <listener-class>org.apache.tomcat.websocket.server.WsContextListener</listener-class> </listener>
然后实现ServerApplicationConfig接口,实现如下:
/* * */ package com.config.websocket.client; import java.util.HashSet; import java.util.Set; import javax.websocket.Endpoint; import javax.websocket.server.ServerApplicationConfig; import javax.websocket.server.ServerEndpointConfig; public class ScanWebSocketSeverConfig implements ServerApplicationConfig { @Override public Set<ServerEndpointConfig> getEndpointConfigs(Set<Class<? extends Endpoint>> scanned) { Set<ServerEndpointConfig> result = new HashSet<ServerEndpointConfig>(); /* if (scanned.contains(EchoWsChatSever.class)) { result.add(ServerEndpointConfig.Builder.create(EchoWsChatSever.class, "/echo").build()); }*/ return result; } @Override public Set<Class<?>> getAnnotatedEndpointClasses(Set<Class<?>> scanned) { Set<Class<?>> results = new HashSet<Class<?>>(); for (Class<?> clazz : scanned) { if (clazz.getPackage().getName().startsWith("com.websocket.")) { System.out.println("find end point : " + clazz.getName()); results.add(clazz); } } return results; } }
创建网页echo.html,内容如下:
<html> <head> <title>Web Socket Echo Test</title> <script> var ws = null; var count = 0; 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); if(event.data instanceof ArrayBuffer) { var bytes = new Uint8Array(event.data); alert(bytes.length + " : " + bytes[0]); } }; ws.onclose = function (event) { setConnected(false); log('Info: WebSocket connection closed, Code: ' + event.code + (event.reason == "" ? "" : ", Reason: " + event.reason)); }; } function disconnect() { if (ws != null) { ws.doClose(); ws = null; } setConnected(false); } function echo() { if (ws != null) { var message = document.getElementById('message').value; log('Sent: ' + message); ws.send(JSON.stringify({'textMessage': message})); count++ } else { alert('WebSocket connection not established, please connect.'); } } function log(message) { var echomsg = document.getElementById('echomsg'); var p = document.createElement('p'); p.style.wordWrap = 'break-word'; p.appendChild(document.createTextNode(message)); echomsg.appendChild(p); while (echomsg.childNodes.length > 25) { echomsg.removeChild(console.firstChild); } echomsg.scrollTop = console.scrollHeight; } document.addEventListener("DOMContentLoaded", function() { // Remove elements with "noscript" class - <noscript> is not allowed in XHTML var noscripts = document.getElementsByClassName("noscript"); for (var i = 0; i < noscripts.length; i++) { noscripts[i].parentNode.removeChild(noscripts[i]); } }, false); </script> </head> <body> <div> <h4>URL - ws://localhost:8080/websocket/echo</h4> <input id="target" type="text" size="40" style="width: 350px" /> </div> <div> <button id="connect" οnclick="connect();">Connect</button> <button id="disconnect" disabled="disabled" οnclick="disconnect();">Disconnect</button> </div> <div> <textarea id="message" style="width: 350px">Here is a message!</textarea> </div> <div> <button id="echo" οnclick="echo();" disabled="disabled">Echo message</button> </div> <div id="echomsg"> </div> </body> </html>
三 :运行与测试
打包部署到tomcat之后,启动chrom浏览器,输入地址:
http://localhost:8080/websocket/echo.html
后来,我还发现,tomcat实现websocket服务器端居然不支持子协议
跟3W上的测试URL结果不一样。