websocket协议是近些年随html5发展而诞生的，主要用于解决web服务器与客户端无法双向交互的问题。如今已经被W3C收入标准协议。

服务器支持：tomcat、jetty的最新版本都已支持websocket；如果不想更换现有服务器，也可用spring4.0作为替代。据说新版本的jre将收入websocket类，没具体接触。

客户端支持：目前的主流浏览器都已经实现了websocket，但由于前期协议版本变化太快，很多厂商没有跟上。android默认浏览器就不支持websocket，IE也直到IE10才支持。

网上已有通过html实现websocket client的例子，这里我们用java实现客户端连接。废话不说，上Demo：

1.服务器端

服务器用了tomcat 7.0，直接使用tomcat的websocket实现

1）连接管理类

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.ArrayList;
import java.util.List;
import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.WsOutbound;

public class MessageCenter
{
private static MessageCenter instance = new MessageCenter();

private List socketList;

private MessageCenter()
{
this.socketList = new ArrayList();
}

public static MessageCenter getInstance()
{
return instance;
}

public void addMessageInbound(MessageInbound inbound)
{
socketList.add(inbound);
}

public void removeMessageInbound(MessageInbound inbound)
{
socketList.remove(inbound);
}

public void broadcast(CharBuffer msg) throws IOException
{
for (MessageInbound messageInbound : socketList)
{
CharBuffer buffer = CharBuffer.wrap(msg);
WsOutbound outbound = messageInbound.getWsOutbound();
outbound.writeTextMessage(CharBuffer.wrap("broadcasting:" + msg));
// outbound.writeTextMessage(buffer);
outbound.flush();
}
}
}

2）消息入口类

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.util.Date;

import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.WsOutbound;

public class MyMessageInbound extends MessageInbound {

@Override
protected void onBinaryMessage(ByteBuffer arg0) throws IOException {
// TODO Auto-generated method stub

}

@Override
protected void onTextMessage(CharBuffer msg) throws IOException {
System.out.println("Received:"+msg);
MessageCenter.getInstance().broadcast(msg);

}

@Override
protected void onClose(int status) {
System.out.println("close:"+new Date());
MessageCenter.getInstance().removeMessageInbound(this);
super.onClose(status);
}

@Override
protected void onOpen(WsOutbound outbound) {
System.out.println("open :"+new Date());
super.onOpen(outbound);
MessageCenter.getInstance().addMessageInbound(this);
}
}

3）Websocket servlet

import javax.servlet.http.HttpServletRequest;

import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;

public class MeWebSocketServlet extends WebSocketServlet
{

private static final long serialVersionUID = -7178893327801338294L;

@Override
protected StreamInbound createWebSocketInbound(String subProtocol, HttpServletRequest request)
{
System.out.println("##########client login#########");
return new MeMessageInbound();
}

}

4）添加servlet到web.xml

< servlet>
< servlet-name> android
< servlet-class> MyWebSocketServlet

< servlet-mapping>
< servlet-name> android
< url-pattern> *.do

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