Socket Programming on Android

Socket 编程基础知识：
主要分服务器端编程和客户端编程。
服务器端编程步骤：
1： 创建服务器端套接字并绑定到一个端口上（0-1023是系统预留的，最好大约1024）
2： 套接字设置监听模式等待连接请求
3： 接受连接请求后进行通信
4： 返回，等待赢一个连接请求

客户端编程步骤：
1： 创建客户端套接字（指定服务器端IP地址与端口号）
2： 连接（Android 创建Socket时会自动连接）
3： 与服务器端进行通信
4： 关闭套接字

Android Socket 通信原理注意：
1： 中间的管道连接是通过InputStream/OutputStream流实现的。
2： 一旦管道建立起来可进行通信
3： 关闭管道的同时意味着关闭Socket
4： 当对同一个Socket创建重复管道时会异常
5： 通信过程中顺序很重要：服务器端首先得到输入流，然后将输入流信息输出到其各个客户端
    客户端先建立连接后先写入输出流，然后再获得输入流。不然活有EOFException的异常。

下面是关于在服务器端编程的代码：

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;

/**
 *@author Andrew.Lee
 *@create 2011-6-1 下午04:45:19
 *@version 1.0
 *@see
 */
public class Server {
    static ServerSocket aServerSocket = null; // Server Socet.
    DataInputStream aDataInput = null; // Server input Stream that to
    // receive msg from client.
    DataOutputStream aDataOutput = null; // Server output Stream that to
    static ArrayList list = new ArrayList();

    public static void main(String[] args) {
        try {
            aServerSocket = new ServerSocket(50003); // listen 8888 port.
            System.out.println("already listen 50003 port.");
        } catch (Exception e) {
            e.printStackTrace();
        }
        int num = 0;
        while (num < 10) {
            Socket aSessionSoket = null;
            try {
                aSessionSoket = aServerSocket.accept();
                MyThread thread = new Server().new MyThread(aSessionSoket);
                thread.start();
                num = list.size();
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        }
    }

    class MyThread extends Thread {
        Socket aSessionSoket = null;

        public MyThread(Socket socket) {
            aSessionSoket = socket;
        }

        public void run() {
            try {
                aDataInput = new DataInputStream(aSessionSoket.getInputStream());
                aDataOutput = new DataOutputStream(aSessionSoket
                        .getOutputStream());
                list.add(aDataOutput);
                while (true) {
                    String msg = aDataInput.readUTF(); // read msg.
                    if (!msg.equals("connect...")) {
                        System.out.println("ip: "
                                + aSessionSoket.getInetAddress());// ip.
                        System.out.println("receive msg: " + msg);
                        for (int i = 0; i < list.size(); i++) {
                            DataOutputStream output = (DataOutputStream) list
                                    .get(i);
                            output.writeUTF(msg + "----" + list.size());
                        }
                        if (msg.equals("end"))
                            break;
                    }
                    aDataOutput.writeUTF("");
                }

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                try {
                    aDataInput.close();
                    if (aDataOutput != null)
                        aDataOutput.close();
                    list.remove(aDataOutput);
                    aSessionSoket.close();

                } catch (Exception e2) {
                    e2.printStackTrace();
                }

            }

        }
    }
}

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;

/**
 *@author Andrew.Lee
 *@create 2011-6-1 下午04:45:19
 *@version 1.0
 *@see
 */
public class Server {
	static ServerSocket aServerSocket = null; // Server Socet.
	DataInputStream aDataInput = null; // Server input Stream that to
	// receive msg from client.
	DataOutputStream aDataOutput = null; // Server output Stream that to
	static ArrayList list = new ArrayList();

	public static void main(String[] args) {
		try {
			aServerSocket = new ServerSocket(50003); // listen 8888 port.
			System.out.println("already listen 50003 port.");
		} catch (Exception e) {
			e.printStackTrace();
		}
		int num = 0;
		while (num < 10) {
			Socket aSessionSoket = null;
			try {
				aSessionSoket = aServerSocket.accept();
				MyThread thread = new Server().new MyThread(aSessionSoket);
				thread.start();
				num = list.size();
			} catch (IOException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
		}
	}

	class MyThread extends Thread {
		Socket aSessionSoket = null;

		public MyThread(Socket socket) {
			aSessionSoket = socket;
		}

		public void run() {
			try {
				aDataInput = new DataInputStream(aSessionSoket.getInputStream());
				aDataOutput = new DataOutputStream(aSessionSoket
						.getOutputStream());
				list.add(aDataOutput);
				while (true) {
					String msg = aDataInput.readUTF(); // read msg.
					if (!msg.equals("connect...")) {
						System.out.println("ip: "
								+ aSessionSoket.getInetAddress());// ip.
						System.out.println("receive msg: " + msg);
						for (int i = 0; i < list.size(); i++) {
							DataOutputStream output = (DataOutputStream) list
									.get(i);
							output.writeUTF(msg + "----" + list.size());
						}
						if (msg.equals("end"))
							break;
					}
					aDataOutput.writeUTF("");
				}

			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} finally {
				try {
					aDataInput.close();
					if (aDataOutput != null)
						aDataOutput.close();
					list.remove(aDataOutput);
					aSessionSoket.close();

				} catch (Exception e2) {
					e2.printStackTrace();
				}

			}

		}
	}
}

注意问题：为了实现对于多个客户端的处理，使用了多线程的操作，每个线程维护一个Socket的连接与通信，新连接的Socket的管道被加入到ArrayList中。对于输出流的操作是对于所有的连接的客户端进行写数据。对于关闭了Socket的客户端管道从List中移除。
客户端编程代码：

package com.daisy.android.network;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.UnknownHostException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

/**
 *@author Andrew.Lee
 *@create 2011-5-28 下午02:26:20
 *@version 1.0
 *@see
 */

public class SocketActivity extends Activity {
    EditText editText = null;
    Button sendButton = null;
    TextView display = null;
    Socket client = null;
    MyHandler myHandler;
    DataOutputStream dout;
    DataInputStream din;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.clientsocket);
        editText = (EditText) findViewById(R.id.message);
        sendButton = (Button) findViewById(R.id.send);
        display = (TextView) findViewById(R.id.display);
        sendButton.setOnClickListener(listener);
        try {
            client = new Socket("192.168.0.120", 50003);
            dout = new DataOutputStream(client.getOutputStream());
            din = new DataInputStream(client.getInputStream());
        } catch (UnknownHostException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        myHandler = new MyHandler();

        MyThread m = new MyThread();
        m.start();
    }

    class MyHandler extends Handler {
        public MyHandler() {
        }

        // 子类必须重写此方法,接受数据
        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            Log.d("MyHandler", "handleMessage......");
            super.handleMessage(msg);
            // 此处可以更新UI

            if (client != null && client.isConnected()) {
                Log.i("handler..", "*-----*");
                try {
                    dout.writeUTF("connect...");
                    String message = din.readUTF();
                    if (!message.equals(""))
                        display.setText(display.getText().toString() + "\n"
                                + "服务器发来的消息--：" + message);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

        }
    }

    class MyThread extends Thread {
        public void run() {
            while (true) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                Message msg = new Message();
                SocketActivity.this.myHandler.sendMessage(msg);
            }
        }
    }

    OnClickListener listener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            String sendText = editText.getText().toString();
            try {
                // din = new DataInputStream(client.getInputStream());
                dout.writeUTF(sendText);
                /*
                 * display.setText(display.getText().toString() + "\n" +
                 * "服务器发来的消息：" + din.readUTF());
                 */
                /*
                 * display.setText(display.getText().toString() + "\n" +
                 * "服务器发来的消息--：" + din.readUTF());
                 */
            } catch (UnknownHostException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    };
}

package com.daisy.android.network;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.UnknownHostException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

/**
 *@author Andrew.Lee
 *@create 2011-5-28 下午02:26:20
 *@version 1.0
 *@see
 */

public class SocketActivity extends Activity {
	EditText editText = null;
	Button sendButton = null;
	TextView display = null;
	Socket client = null;
	MyHandler myHandler;
	DataOutputStream dout;
	DataInputStream din;

	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.clientsocket);
		editText = (EditText) findViewById(R.id.message);
		sendButton = (Button) findViewById(R.id.send);
		display = (TextView) findViewById(R.id.display);
		sendButton.setOnClickListener(listener);
		try {
			client = new Socket("192.168.0.120", 50003);
			dout = new DataOutputStream(client.getOutputStream());
			din = new DataInputStream(client.getInputStream());
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

		myHandler = new MyHandler();

		MyThread m = new MyThread();
		m.start();
	}

	class MyHandler extends Handler {
		public MyHandler() {
		}

		// 子类必须重写此方法,接受数据
		@Override
		public void handleMessage(Message msg) {
			// TODO Auto-generated method stub
			Log.d("MyHandler", "handleMessage......");
			super.handleMessage(msg);
			// 此处可以更新UI

			if (client != null && client.isConnected()) {
				Log.i("handler..", "*-----*");
				try {
					dout.writeUTF("connect...");
					String message = din.readUTF();
					if (!message.equals(""))
						display.setText(display.getText().toString() + "\n"
								+ "服务器发来的消息--：" + message);
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}

		}
	}

	class MyThread extends Thread {
		public void run() {
			while (true) {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				Message msg = new Message();
				SocketActivity.this.myHandler.sendMessage(msg);
			}
		}
	}

	OnClickListener listener = new OnClickListener() {

		@Override
		public void onClick(View v) {
			// TODO Auto-generated method stub
			String sendText = editText.getText().toString();
			try {
				// din = new DataInputStream(client.getInputStream());
				dout.writeUTF(sendText);
				/*
				 * display.setText(display.getText().toString() + "\n" +
				 * "服务器发来的消息：" + din.readUTF());
				 */
				/*
				 * display.setText(display.getText().toString() + "\n" +
				 * "服务器发来的消息--：" + din.readUTF());
				 */
			} catch (UnknownHostException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	};
}

注意：为实现对于UI的间歇性刷新操作，使用到了Handler的消息机制。

附注：以上只是对Android的Socket编程的大致思路和过程，其中缺少了对于InputStream/OututStream 的异常处理，连接超时等处理。