Socket（套接字）是一種通信機制，可以實現單機或跨網絡進行通信，其創建需要明確的區分C（客戶端）/S（服務器端），支持多個客戶端連接到同一個服務器。有兩種傳輸模式：

1）、面向連接的傳輸：基於TCP協議，可靠性高，但效率低；

2）、面向無連接的傳輸：基於UDP協議，可靠性低，但效率高；

Android中，直接采用Socket通信應該是我們遇到的最低級的網絡運用。盡管已經作了很大程度的抽象，但是純粹的Socket通信，仍然給開發者留下很多細節需要處理，尤其在服務器端，開發者需要處理多線程以及數據緩沖等的設計問題。相對而言，處於更高抽象層的HTTP等，已經對Socket通信中需要處理的技術細節進行了很好的封裝，開發者無須關心，因此，HTTP在網絡開發中通常具有決定性的優勢。

Android在其核心庫的java包中，提供了用於客戶端的Socket class和用於服務器端的ServerSocket class，分別位於$SOURCE/libcore/luni/src/main/java/java/net/Socket.java和$SOURCE/libcore/luni/src/main/java/java/net/ServerSocket.java文件中。分析兩個class的源碼，可以看出封裝考慮的很全面，只構造方法一向每個class都考慮了很多種使用情況。由於本人只是初學者，很多理解的不深入，這裡只拋磚引玉的對兩個class的構造方法分別介紹一種，就是我下面的程序中用到的：

Socket(String dstName, int dstPort)：創建一個以流的方式（基於TCP協議）連接到目標機（這裡可以理解為服務器）的客戶端Socket；dstName是目標機的IP地址，dstPort是要連接的目標機的端 口號。這裡要注意對端口的理解，它不能理解為物理上的一個接口，而是對計算機中一塊特殊內存區域的形象表述。

ServerSocket(int aport)：創建一個綁定到本機指定端口的服務端Socket；aport就是指定的本機端口。與上述客戶端Socket對應，通過TCP連接時，ServerSocket創建後需要在aport端口上進行監聽，等待客戶端的連接。

啟動 service 和 activity

mContext.startService(new Intent(mContext, SocketService.class));

Intent intent = new Intent();
intent.setClass(mContext, SocketClientDemo.class);
mContext.startActivity(intent);

service ：服務端

package com.android.settings;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;

public class SocketService extends Service {
Thread mServiceThread;

Socket client;

@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}

@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();

mServiceThread = new Thread(new SocketServerThread());
}

@Override
public void onStart(Intent intent, int startId) {
// TODO Auto-generated method stub
super.onStart(intent, startId);

mServiceThread.start();
}

@Override
public void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
}

public class SocketServerThread extends Thread {
private static final int PORT = 54321;

private SocketServerThread() {
}

@Override
public void run() {
try {
ServerSocket server = new ServerSocket(PORT);

while (true) {
System.out.println("tian begin client connected");
client = server.accept();
System.out.println(" tian client connected");

BufferedReader reader = new BufferedReader(
new InputStreamReader(client.getInputStream()));
System.out.println(" tian read from client:");

String textLine = reader.readLine();
if (textLine.equalsIgnoreCase("EXIT")) {
System.out
.println(" tian EXIT invoked, closing client");
break;
}

System.out.println(textLine);

PrintWriter writer = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(client.getOutputStream())));

System.out.println(" return tian read from client:"
+ textLine);
writer.println(" tian ECHO from server: " + textLine);
writer.flush();

writer.close();
reader.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
System.err.println(e);
}
}

}
}

package com.android.settings;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
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;

public class SocketClientDemo extends Activity {
private static final String SERVERIP = "127.0.0.1";
private static final int SERVERPORT = 54321;

private static final String TAG = "SocketClientDemo";

TextView mMsgRev;
EditText mMsgEdit;
Button mMsgSendBtn;

String mSendMsg;
String mReceivedMsg;

class MyThread implements Runnable {
private String name;

public MyThread(String name) {
this.name = name;
}

public void run() {
// for (int i = 0; i < 100; i++) {
// System.out.println("線程開始：" + this.name + ",i=" + i);

Log.d(TAG, "MyThread execu");
// }
}
};

class MyThread2 extends Thread {

@Override
public void run() {
// TODO Auto-generated method stub
Log.d(TAG, "MyThread2 execu");
}
};

class MyThread3 extends Thread {

private String name;

public MyThread3(String name) {
// super();
this.name = name;
}

@Override
public void run() {
// TODO Auto-generated method stub
Log.d(TAG, "MyThread3 execu" + "name=" + name);

Socket socket = null;
mSendMsg = mMsgEdit.getText().toString();

try {
socket = new Socket(SERVERIP, SERVERPORT);

PrintWriter writer = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())));
writer.println(mSendMsg);
writer.flush();

BufferedReader reader = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
mReceivedMsg = reader.readLine();

Message meaage = mHander.obtainMessage();
meaage.arg1 = 1;
mHander.sendMessage(meaage);

writer.close();
reader.close();
socket.close();
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.xml.beidou_detail_preference_settings);

mMsgRev = (TextView) findViewById(R.id.receive_msg);
mMsgEdit = (EditText) findViewById(R.id.edit_msg);
mMsgSendBtn = (Button) findViewById(R.id.send_msg);

mMsgSendBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {

/*
* MyThread thread = new MyThread("00"); new
* Thread(thread).start();
*
* new MyThread2().start();
*/

MyThread3 thread3 = new MyThread3("33");
thread3.start();

}
});
}

final Handler mHander = new Handler() {

@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub

if (mReceivedMsg != null) {
mMsgRev.setText(mReceivedMsg);
} else {
mMsgRev.setText("tian receive data error");
}
super.handleMessage(msg);
}

};
}

activity : 客戶端

package com.android.settings;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
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;

public class SocketClientDemo extends Activity {
private static final String SERVERIP = "127.0.0.1";
private static final int SERVERPORT = 54321;

private static final String TAG = "SocketClientDemo";

TextView mMsgRev;
EditText mMsgEdit;
Button mMsgSendBtn;

String mSendMsg;
String mReceivedMsg;

class MyThread implements Runnable {
private String name;

public MyThread(String name) {
this.name = name;
}

public void run() {
// for (int i = 0; i < 100; i++) {
// System.out.println("線程開始：" + this.name + ",i=" + i);

Log.d(TAG, "MyThread execu");
// }
}
};

class MyThread2 extends Thread {

@Override
public void run() {
// TODO Auto-generated method stub
Log.d(TAG, "MyThread2 execu");
}
};

class MyThread3 extends Thread {

private String name;

public MyThread3(String name) {
// super();
this.name = name;
}

@Override
public void run() {
// TODO Auto-generated method stub
Log.d(TAG, "MyThread3 execu" + "name=" + name);

Socket socket = null;
mSendMsg = mMsgEdit.getText().toString();

try {
socket = new Socket(SERVERIP, SERVERPORT);

PrintWriter writer = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())));
writer.println(mSendMsg);
writer.flush();

BufferedReader reader = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
mReceivedMsg = reader.readLine();

Message meaage = mHander.obtainMessage();
meaage.arg1 = 1;
mHander.sendMessage(meaage);

writer.close();
reader.close();
socket.close();
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.xml.beidou_detail_preference_settings);

mMsgRev = (TextView) findViewById(R.id.receive_msg);
mMsgEdit = (EditText) findViewById(R.id.edit_msg);
mMsgSendBtn = (Button) findViewById(R.id.send_msg);

mMsgSendBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {

/*
* MyThread thread = new MyThread("00"); new
* Thread(thread).start();
*
* new MyThread2().start();
*/

MyThread3 thread3 = new MyThread3("33");
thread3.start();

}
});
}

final Handler mHander = new Handler() {

@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub

if (mReceivedMsg != null) {
mMsgRev.setText(mReceivedMsg);
} else {
mMsgRev.setText("tian receive data error");
}
super.handleMessage(msg);
}

};
}