利用websocket實現android消息推送
前段時間做一個項目，需要android客戶端作為管理工具與web服務器后臺實時交互，想了很多方法，包括androidpn、openfire+smack、xmpp協議，要么太繁瑣，要么無法滿足實時性。想來還是用socket，經人提醒想到了websocket。
websocket協議是近些年隨html5發展而誕生的，主要用于解決web服務器與客戶端無法雙向交互的問題。如今已經被W3C收入標準協議。
服務器支持：tomcat、jetty的最新版本都已支持websocket；如果不想更換現有服務器，也可用spring4.0作為替代。據說新版本的jre將收入websocket類，沒具體接觸。
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客戶端支持：目前的主流瀏覽器都已經實現了websocket，但由于前期協議版本變化太快，很多廠商沒有跟上。android默認瀏覽器就不支持websocket，IE也直到IE10才支持。
網上已有通過html實現websocket client的例子，這里我們用java實現客戶端連接。廢話不說，上Demo：
1.服務器端
服務器用了tomcat 7.0，直接使用tomcat的websocket實現
1）連接管理類
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(); } }}</pre></div>
2）消息入口類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); }}</pre>
</div>3）Websocket servletimport 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(); }}</pre>
</div>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.客戶端客戶端使用java實現websocket client，網上有人實現了Java-websocket：https://github.com/TooTallNate/Java-WebSocket 可以取得源碼，用maven編譯。最新jar包下載地址：
引用jar包后，實現簡單消息連接：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(); }}</pre></div>
注意，連接中使用的new Draft_17()就是使用的協議version，Tomcat 7.0的協議版本需要高于Draft_17。
總結websocket的利弊優點：與socket相比，可以節省額外的端口占用，直接使用一個公網域名訪問。另外協議對報文的流量消耗做了優化。
缺點：畢竟websocket底層也是socket連接，因而當大并發用戶連接時目測會消耗較多資源。
參考：Tomcat 7.0 api http://tomcat.apache.org/tomcat-7.0-doc/api/
來自：http://blog.csdn.net/chifengxin/article/details/14521093本文由用戶 jopen 自行上傳分享，僅供網友學習交流。所有權歸原作者，若您的權利被侵害，請聯系管理員。轉載本站原創文章，請注明出處，并保留原始鏈接、圖片水印。本站是一個以用戶分享為主的開源技術平臺，歡迎各類分享！相關經驗
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