ch34 网络编程(二)UDP通信.doc

J2ME程序设计之网络编程（二）UDP通信UDP编程知识UDP是什么?UDP是数据报，只负责传输信息，并不保证信息一定会被收到，TCP基于连接，UDP基于报文。UDP通信开发流程：1.服务器监听某个端口2.客户端连接服务器某个端口3.通过Datagram通信服务器监听某个端口：javax.microedition.io.UDPDatagramConnectionjavax.microedition.io.Connector专门负责建立各种连接open(“datagram:/:端口”),返回UDPDatagramConnectionUDPDatagramConnection可以获得服务器IP和端口客户端连接服务器端javax.microedition.io.Connector专门负责建立各种连接open(“datagram:/IP地址:端口”),返回UDPDatagramConnectionUDPDatagramConnection重要方法:1newDatagram()2receive()3send()【案例1】客户端与服务器端建立连接ServerMIDlet1.java文件import javax.microedition.io.Connector; import javax.microedition.io.UDPDatagramConnection;import javax.microedition.midlet.MIDlet; import javax.microedition.midlet.MIDletStateChangeException;public class ServerMIDlet1 extends MIDlet protected void startApp() throws MIDletStateChangeException try/监听端口UDPDatagramConnection udc = (UDPDatagramConnection)Connector.open(datagram:/:9999);/System.out.println(IP + udc.getLocalAddress();/System.out.println(端口 + udc.getLocalPort();catch(Exception ex)ex.printStackTrace();ClientMIDLet1.java文件import javax.microedition.io.Connector; import javax.microedition.io.UDPDatagramConnection;import javax.microedition.midlet.MIDlet;import javax.microedition.midlet.MIDletStateChangeException;public class ClientMIDlet1 extends MIDlet protected void startApp() throws MIDletStateChangeException try/连接到服务器端UDPDatagramConnection udc = (UDPDatagramConnection)Connector.open(datagram:/127.0.0.1:9999);catch(Exception ex)ex.printStackTrace();【案例2】客户端连接服务器，在服务器显示客户端信息ServerMIDlet2.java文件import javax.microedition.midlet.MIDletStateChangeException;public class ServerMIDlet2 extends MIDlet private final int MAX = 255;protected void startApp() throws MIDletStateChangeException try/监听端口UDPDatagramConnection udc = (UDPDatagramConnection)Connector.open(datagram:/:9999);/接受数据报Datagram dg = udc.newDatagram(MAX);udc.receive(dg);byte data = dg.getData();System.out.println(new String(data,0,dg.getLength();catch(Exception ex)ex.printStackTrace();ClientMIDlet2文件public class ClientMIDlet2 extends MIDlet protected void startApp() throws MIDletStateChangeException try/连接到服务器端UDPDatagramConnection udc = (UDPDatagramConnection)Connector.open(datagram:/127.0.0.1:9999);/送给服务器一个数据报String str = 我是客户端;Datagram dg = udc.newDatagram(str.getBytes(), str.getBytes().length);udc.send(dg);/送给服务器端catch(Exception ex)ex.printStackTrace();【案例3】客户端与服务器聊天，使用UDP实现ChatServerMIDlet.java文件public class ChatServerMIDlet extends MIDlet implements CommandListener,Runnableprivate TextField tfMsg = new TextField(输入聊天信息,255,TextField.ANY);private Command cmdSend = new Command(发送,Command.SCREEN,1);private Form frmChat = new Form(聊天界面);private Display display;private UDPDatagramConnection udc = null;private final int MAX = 255;private String address;protected void startApp() throws MIDletStateChangeException display = Display.getDisplay(this);display.setCurrent(frmChat);frmChat.addCommand(cmdSend);frmChat.append(tfMsg);frmChat.setCommandListener(this);tryudc = (UDPDatagramConnection)Connector.open(datagram:/:9999);new Thread(this).start();catch(Exception ex)ex.printStackTrace();public void commandAction(Command c,Displayable d)if(c=cmdSend)/发送String msg = tfMsg.getString();tryDatagram dg = udc.newDatagram(msg.getBytes(), msg.getBytes().length);dg.setAddress(address);udc.send(dg);catch(Exception ex)ex.printStackTrace();public void run()while(true)tryDatagram dg = udc.newDatagram(MAX);udc.receive(dg);address = dg.getAddress();String msg = new String(dg.getData(),0,dg.getLength();frmChat.append(msg + n);catch(Exception ex)ex.printStackTrace();ChatClientMIDlet.java文件public class ChatClientMIDlet extends MIDlet implements CommandListener,Runnableprivate TextField tfMsg = new TextField(输入聊天信息,255,TextField.ANY);private Command cmdSend = new Command(发送,Command.SCREEN,1);private Form frmChat = new Form(聊天界面);private Display display;private UDPDatagramConnection udc = null;private final int MAX = 255;protected void startApp() throws MIDletStateChangeException display = Display.getDisplay(this);display.setCurrent(frmChat);frmChat.addCommand(cmdSend);frmChat.append(tfMsg);frmChat.setCommandListener(this);tryudc = (UDPDatagramConnection)Connector.open(datagram:/127.0.0.1:9999);new Thread(this).start();catch(Exception ex)ex.printStackTrace();public void commandAction(Command c,Displayable d)if(c=cmdSend)/发送String msg = tfMsg.getString();tryDatagram dg = udc.newDatagram(msg.getBytes(), msg.getBytes().length);udc.send(dg);catch(Except