J2ME中使用Socket开发联网程序

1/5/2008来源:Java教程人气:6286


  在J2ME中基于UDP协议编程一文中介绍了如何使用Datagram和DatagramConnection来开发应用程序,本文将主要讲述在MIDP2.0中使用ServerSocketConnection和SocketConnection来开发联网应用程序。TCP协议是可以保证传输的质量的,这也是他和UDP的一大区别。由于以上谈到的四个类都属于GCF,他们在程序编写方面也非常相似,通常我们在Server端的某个端口监听,当客户端连接服务器的时候,则可以得到一个SocketConnection的实例。通过两端的SocketConnection则可以实现C/S结构的通信了。

  首先看一下,ServerSocketConnection类,它的一个非常重要的方法就是acceptAndOpen()方法,这个方法返回一个SocketConnection实例,从而使得客户端和服务器端可以通过socket通信了。典型的代码如下:

// Create the server listening socket for port 1234
ServerSocketConnection scn = (ServerSocketConnection)
Connector.open("socket://:1234");

// Wait for a connection.
SocketConnection sc = (SocketConnection) scn.acceptAndOpen();

// Set application specific hints on the socket.
sc.setSocketOption(DELAY, 0);
sc.setSocketOption(LINGER, 0);
sc.setSocketOption(KEEPALIVE, 0);
sc.setSocketOption(RCVBUF, 128);
sc.setSocketOption(SNDBUF, 128);

// Get the input stream of the connection.
DataInputStream is = sc.openDataInputStream();

// Get the output stream of the connection.
DataOutputStream os = sc.openDataOutputStream();

// Read the input data.
String result = is.readUTF();

// Echo the data back to the sender.
os.writeUTF(result);

// Close everything.
is.close();
os.close();
sc.close();
scn.close();
..


SocketConnection的使用也是非常简单,通过Connector的open方法我们可以得到一个SocketConnection的实例。
SocketConnection sc = (SocketConnection)
Connector.open("socket://host.com:79");
sc.setSocketOption(SocketConnection.LINGER, 5);

InputStream is = sc.openInputStream();
OutputStream os = sc.openOutputStream();

os.write("\r\n".getBytes());
int ch = 0;
while(ch != -1) {
 ch = is.read();
}

is.close();
os.close();
sc.close();
  其实我们在用socket编写程序的时候无非遵循这样的一种规则:服务器端建立监听端口等待连接,客户端通过open()方法与服务器端建立连接,两端通过建立的socket传输数据,关闭连接。
  下图是我在运行WTK中NetworkDemo的时候的截图!代码也一并发表出来。

J2ME中使用Socket开发联网程序

package socket;

import javax.microedition.midlet.*;
import javax.microedition.io.*;
import javax.microedition.lcdui.*;
import java.io.*;

public class SocketMIDlet extends MIDlet implements CommandListener {
 PRivate static final String SERVER = "Server";
 private static final String CLIENT = "Client";
 private static final String[] names = { SERVER, CLIENT };
 private static Display display;
 private Form f;
 private ChoiceGroup cg;
 private boolean isPaused;
 private Server server;
 private Client client;
 private Command exitCommand = new Command("Exit", Command.EXIT, 1);
 private Command startCommand = new Command("Start", Command.ITEM, 1);

 public SocketMIDlet() {
  display = Display.getDisplay(this);
  f = new Form("Socket Demo");
  cg = new ChoiceGroup("Please select peer", Choice.EXCLUSIVE, names,null);
  f.append(cg);

  f.addCommand(exitCommand);
  f.addCommand(startCommand);
  f.setCommandListener(this);

  display.setCurrent(f);
 }

 public boolean isPaused() {
  return isPaused;
 }

 public void startApp() {
  isPaused = false;
 }

 public void pauseApp() {
  isPaused = true;
 }

 public void destroyApp(boolean unconditional) {
  if (server != null) {
   server.stop();
  }
  if (client != null) {
   client.stop();
  }
 }

 public void commandAction(Command c, Displayable s) {
  if (c == exitCommand) {
   destroyApp(true);
   notifyDestroyed();
  } else if (c == startCommand) {
   String name = cg.getString(cg.getSelectedIndex());
   if (name.equals(SERVER)) {
    server = new Server(this);
    server.start();
   } else {
    client = new Client(this);
    client.start();
   }
  }
 }

}

package socket;

import javax.microedition.midlet.*;
import javax.microedition.io.*;
import javax.microedition.lcdui.*;
import java.io.*;

public class Server implements Runnable, CommandListener {
 private SocketMIDlet parent;
 private Display display;
 private Form f;
 private StringItem si;
 private TextField tf;
 private boolean stop;
 private Command sendCommand = new Command("Send", Command.ITEM, 1);
 private Command exitCommand = new Command("Exit", Command.EXIT, 1);
 InputStream is;
 OutputStream os;
 SocketConnection sc;
 ServerSocketConnection scn;
 Sender sender;
 
 public Server(SocketMIDlet m) {
  parent = m;
  display = Display.getDisplay(parent);
  f = new Form("Socket Server");
  si = new StringItem("Status:", " ");
  tf = new TextField("Send:", "", 30, TextField.ANY);
  f.append(si);
  f.append(tf);
  f.addCommand(exitCommand);
  f.setCommandListener(this);
  display.setCurrent(f);
 }

 public void start() {
  Thread t = new Thread(this);
  t.start();
 }

 public void run() {
  try {
   si.setText("Waiting for connection");
   scn = (ServerSocketConnection) Connector.open("socket://:5009");

   // Wait for a connection.
   sc = (SocketConnection) scn.acceptAndOpen();
   si.setText("Connection accepted");
   is = sc.openInputStream();
   os = sc.openOutputStream();
   sender = new Sender(os);
 
   // Allow sending of messages only after Sender is created
   f.addCommand(sendCommand);

   while (true) {
    StringBuffer sb = new StringBuffer();
    int c = 0;

    while (((c = is.read()) != '\n') && (c != -1)) {
     sb.append((char) c);
    }

    if (c == -1) {
     break;
    }
    si.setText("Message received - " + sb.toString());
   }
   stop();
   si.setText("Connection is closed");
   f.removeCommand(sendCommand);
  } catch (IOException ioe) {
   if (ioe.getMessage().equals("ServerSocket Open")) {
    Alert a = new Alert("Server", "Port 5000 is already taken.",null, AlertType.ERROR);
    a.setTimeout(Alert.FOREVER);
    a.setCommandListener(this);
    display.setCurrent(a);
   } else {
    if (!stop) {
     ioe.printStackTrace();
    }
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
 }

 public void commandAction(Command c, Displayable s) {
  if (c == sendCommand && !parent.isPaused()) {
   sender.send(tf.getString());
  }

  if ((c == Alert.DISMISS_COMMAND) (c == exitCommand)) {
   parent.notifyDestroyed();
   parent.destroyApp(true);
  }
 }

/**
* Close all open streams
*/

 public void stop() {
  try {
   stop = true;

   if (is != null) {
    is.close();
   }

   if (os != null) {
    os.close();
   }

   if (sc != null) {
    sc.close();
   }

   if (scn != null) {
    scn.close();
   }
  } catch (IOException ioe) {
 }
}
}

package socket;

import javax.microedition.midlet.*;
import javax.microedition.io.*;
import javax.microedition.lcdui.*;
import java.io.*;

public class Client implements Runnable, CommandListener {
 private SocketMIDlet parent;
 private Display display;
 private Form f;
 private StringItem si;
 private TextField tf;
 private boolean stop;
 private Command sendCommand = new Command("Send", Command.ITEM, 1);
 private Command exitCommand = new Command("Exit", Command.EXIT, 1);

 InputStream is;
 OutputStream os;
 SocketConnection sc;
 Sender sender;

 public Client(SocketMIDlet m) {
  parent = m;
  display = Display.getDisplay(parent);
  f = new Form("Socket Client");
  si = new StringItem("Status:", " ");
  tf = new TextField("Send:", "", 30, TextField.ANY);
  f.append(si);
  f.append(tf);
  f.addCommand(exitCommand);
  f.addCommand(sendCommand);
  f.setCommandListener(this);
  display.setCurrent(f);
 }

 /**
 * Start the client thread
 */
 public void start() {
  Thread t = new Thread(this);
  t.start();
 }

 public void run() {
  try {
   sc = (SocketConnection) Connector.open("socket://localhost:5009");
   si.setText("Connected to server");
   is = sc.openInputStream();
   os = sc.openOutputStream();

   // Start the thread for sending messages - see Sender's main
   // comment for eXPlanation
   sender = new Sender(os);
 
   // Loop forever, receiving data
   while (true) {
    StringBuffer sb = new StringBuffer();
    int c = 0;
    while (((c = is.read()) != '\n') && (c != -1)) {
     sb.append((char) c);
    }

    if (c == -1) {
     break;
    }
    // Display message to user
    si.setText("Message received - " + sb.toString());
   }
   stop();
   si.setText("Connection closed");
   f.removeCommand(sendCommand);
  } catch (ConnectionNotFoundException cnfe) {
   Alert a = new Alert("Client", "Please run Server MIDlet first",null, AlertType.ERROR);
   a.setTimeout(Alert.FOREVER);
   a.setCommandListener(this);
   display.setCurrent(a);
  } catch (IOException ioe) {
   if (!stop) {
    ioe.printStackTrace();
   }
  } catch (Exception e) {
  e.printStackTrace();
 }
}

public void commandAction(Command c, Displayable s) {
 if (c == sendCommand && !parent.isPaused()) {
  sender.send(tf.getString());
 }

 if ((c == Alert.DISMISS_COMMAND) (c == exitCommand)) {
  parent.notifyDestroyed();
  parent.destroyApp(true);
 }
}

/**
* Close all open streams
*/