利用websocket实现android消息推送

  前段时间做一个项目，需要android客户端作为管理工具与web服务器后台实时交互，想了很多方法，包括androidpn、openfire+smack、xmpp协议，要么太繁琐，要么无法满足实时性。想来还是用socket，经人提醒想到了websocket。

 

    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

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

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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

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

2.客户端

    客户端使用java实现websocket client，

    网上有人实现了Java-websocket：https://github.com/TooTallNate/Java-WebSocket 可以取得源码，用maven编译。

    最新jar包下载地址：

    http://download.csdn.net/detail/chifengxin/6524283

 

    引用jar包后，实现简单消息连接：

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import java.net.URI; import java.net.URISyntaxException;   import org.java_websocket.client.WebSocketClient; import org.java_websocket.drafts.Draft; import org.java_websocket.drafts.Draft_10; import org.java_websocket.drafts.Draft_17; import org.java_websocket.framing.Framedata; import org.java_websocket.handshake.ServerHandshake;   /** This example demonstrates how to create a websocket connection to a server. Only the most important callbacks are overloaded. */ public class ExampleClient extends WebSocketClient {           public ExampleClient( URI serverUri , Draft draft ) {                 super( serverUri, draft );         }           public ExampleClient( URI serverURI ) {                 super( serverURI );         }           @Override         public void onOpen( ServerHandshake handshakedata ) {                 System.out.println( "opened connection" );                 // if you plan to refuse connection based on ip or httpfields overload: onWebsocketHandshakeReceivedAsClient         }           @Override         public void onMessage( String message ) {                 System.out.println( "received: " + message );         }           @Override         public void onFragment( Framedata fragment ) {                 System.out.println( "received fragment: " + new String( fragment.getPayloadData().array() ) );         }           @Override         public void onClose( int code, String reason, boolean remote ) {                 // The codecodes are documented in class org.java_websocket.framing.CloseFrame                 System.out.println( "Connection closed by " + ( remote ? "remote peer" : "us" ) );         }           @Override         public void onError( Exception ex ) {                 ex.printStackTrace();                 // if the error is fatal then onClose will be called additionally         }           public static void main( String[] args ) throws URISyntaxException {                 ExampleClient c = new ExampleClient( new URI( "ws://localhost:8080/myweb/android.do" ), new Draft_17() );                 c.connect();         }   }

注意，连接中使用的new Draft_17()就是使用的协议version，Tomcat 7.0的协议版本需要高于Draft_17。

 

总结websocket的利弊

优点：

与socket相比，可以节省额外的端口占用，直接使用一个公网域名访问。另外协议对报文的流量消耗做了优化。

 

缺点：

毕竟websocket底层也是socket连接，因而当大并发用户连接时目测会消耗较多资源。

 

参考：

Tomcat 7.0 api http://tomcat.apache.org/tomcat-7.0-doc/api/