Android网络编程

Android平台有三种网络接口可以使用，他们分别是：java.net.*(标准Java接口)、Org.apache接口和Android.net.*(Android网络接口)。下面分别介绍这些接口的功能和作用。
1.标准Java接口
java.net.*提供与联网有关的类，包括流、数据包套接字(socket)、Internet协议、常见Http处理等。比如：创建URL，以及URLConnection/HttpURLConnection对象、设置链接参数、链接到服务器、向服务器写数据、从服务器读取数据等通信。这些在Java网络编程中均有涉及，我们看一个简单的socket编程，实现服务器回发客户端信息。

服务端：

public class Server implements Runnable{    @Override    public void run() {        Socket socket = null;        try {            ServerSocket server = new ServerSocket(18888);            //循环监听客户端链接请求            while(true){                System.out.println("start...");                //接收请求                socket = server.accept();                System.out.println("accept...");                //接收客户端消息                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));                String message = in.readLine();                //发送消息，向客户端                PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);                out.println("Server:" + message);                //关闭流                in.close();                out.close();            }        } catch (IOException e) {            e.printStackTrace();        }finally{            if (null != socket){                try {                    socket.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }            }    //启动服务器    public static void main(String[] args){        Thread server = new Thread(new Server());        server.start();    }}

客户端 MainActivity

public class MainActivity extends Activity {    private EditText editText;    private Button button;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                editText = (EditText)findViewById(R.id.editText1);        button = (Button)findViewById(R.id.button1);                button.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                Socket socket = null;                String message = editText.getText().toString()+ "\r\n" ;                try {                    //创建客户端socket,注意:不能用localhost或127.0.0.1，Android模拟器把自己作为localhost                    socket = new Socket("192.168.137.1",18888);   //ip地址                    PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter                            (socket.getOutputStream())),true);                    //发送数据                    out.println(message);                                        //接收数据                    BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));                    String msg = in.readLine();                    if (null != msg){                        editText.setText(msg);                        System.out.println(msg);                    }                    else{                        editText.setText("data error");                    }                    out.close();                    in.close();                } catch (UnknownHostException e) {                    e.printStackTrace();                } catch (IOException e) {                    e.printStackTrace();                }                finally{                    try {                        if (null != socket){                            socket.close();                        }                    } catch (IOException e) {                        e.printStackTrace();                    }                }            }        });    }}

布局文件：

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical" android:layout_width="fill_parent"    android:layout_height="fill_parent">    <TextView android:layout_width="fill_parent"        android:layout_height="wrap_content" android:text="@string/hello" />    <EditText android:layout_width="match_parent" android:id="@+id/editText1"        android:layout_height="wrap_content"        android:hint="input the message and click the send button"        ></EditText>    <Button android:text="send" android:id="@+id/button1"        android:layout_width="fill_parent" android:layout_height="wrap_content"></Button></LinearLayout>

启动服务器：

javac com/test/socket/Server.javajava com.test.socket.Server

运行客户端程序：

结果如图：

注意：服务器与客户端无法链接的可能原因有：
没有加访问网络的权限：<uses-permission android:name="android.permission.INTERNET"></uses-permission>