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("<span style="font-weight: bold;">10.0.2.2</span>",18888);
                     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.java
 java 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>
IP地址要使用：10.0.2.2
模拟器不能配置代理。

2。Apache接口
对于大部分应用程序而言JDK本身提供的网络功能已远远不够，这时就需要Android提供的Apache HttpClient了。它是一个开源项目，功能更加完善，为客户端的Http编程提供高效、最新、功能丰富的工具包支持。
下面我们以一个简单例子来看看如何使用HttpClient在Android客户端访问Web。
首先，要在你的机器上搭建一个web应用myapp，只有很简单的一个http.jsp
内容如下：

 <%@page language="java" import="java.util.*" pageEncoding="utf-8"%>
 <html>
 <head>
 <title>
 Http Test
 </title>
 </head>
 <body>
 <%
 String type = request.getParameter("parameter");
 String result = new String(type.getBytes("iso-8859-1"),"utf-8");
 out.println("<h1>" + result + "</h1>");
 %>
 </body>
 </html>

然后实现Android客户端，分别以post、get方式去访问myapp,代码如下：
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:gravity="center"
     android:id="@+id/textView"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:text="@string/hello"
     />
 <Button android:text="get" android:id="@+id/get" android:layout_width="match_parent" android:layout_height="wrap_content"></Button>
 <Button android:text="post" android:id="@+id/post" android:layout_width="match_parent" android:layout_height="wrap_content"></Button>
 </LinearLayout>

资源文件：
strings.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="hello">通过按钮选择不同方式访问网页</string>
     <string name="app_name">Http Get</string>
 </resources>

主Activity:

 public class MainActivity extends Activity {
     private TextView textView;
     private Button get,post;
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);

         textView = (TextView)findViewById(R.id.textView);
         get = (Button)findViewById(R.id.get);
         post = (Button)findViewById(R.id.post);

         //绑定按钮监听器
         get.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View v) {
                 //注意：此处ip不能用127.0.0.1或localhost,Android模拟器已将它自己作为了localhost
                 String uri = "http://192.168.22.28:8080/myapp/http.jsp?parameter=以Get方式发送请求";
                 textView.setText(get(uri));
             }
         });
         //绑定按钮监听器
         post.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View v) {
                 String uri = "http://192.168.22.28:8080/myapp/http.jsp";
                 textView.setText(post(uri));
             }
         });
     }
     /**
      * 以get方式发送请求，访问web
      * @param uri web地址
      * @return 响应数据
      */
     private static String get(String uri){
         BufferedReader reader = null;
         StringBuffer sb = null;
         String result = "";
         HttpClient client = new DefaultHttpClient();
         HttpGet request = new HttpGet(uri);
         try {
             //发送请求，得到响应
             HttpResponse response = client.execute(request);

             //请求成功
             if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                 reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
                 sb = new StringBuffer();
                 String line = "";
                 String NL = System.getProperty("line.separator");
                 while((line = reader.readLine()) != null){
                     sb.append(line);
                 }
             }
         } catch (ClientProtocolException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         }
         finally{
             try {
                 if (null != reader){
                     reader.close();
                     reader = null;
                 }
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
         if (null != sb){
             result =  sb.toString();
         }
         return result;
     }
     /**
      * 以post方式发送请求，访问web
      * @param uri web地址
      * @return 响应数据
      */
     private static String post(String uri){
         BufferedReader reader = null;
         StringBuffer sb = null;
         String result = "";
         HttpClient client = new DefaultHttpClient();
         HttpPost request = new HttpPost(uri);

         //保存要传递的参数
         List<NameValuePair> params = new ArrayList<NameValuePair>();
         //添加参数
         params.add(new BasicNameValuePair("parameter","以Post方式发送请求"));

         try {
             //设置字符集
             HttpEntity entity = new UrlEncodedFormEntity(params,"utf-8");
             //请求对象
             request.setEntity(entity);
             //发送请求
             HttpResponse response = client.execute(request);

             //请求成功
             if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                 System.out.println("post success");
                 reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
                 sb = new StringBuffer();
                 String line = "";
                 String NL = System.getProperty("line.separator");
                 while((line = reader.readLine()) != null){
                     sb.append(line);
                 }
             }
         } catch (ClientProtocolException e) {
             e.printStackTrace();
         } catch (IOException e) {
             e.printStackTrace();
         }
         finally{
             try {
                 //关闭流
                 if (null != reader){
                     reader.close();
                     reader = null;
                 }
             } catch (IOException e) {
                 e.printStackTrace();
             }
         }
         if (null != sb){
             result =  sb.toString();
         }
         return result;
     }
 }

运行结果如下：

3.android.net编程：
常常使用此包下的类进行Android特有的网络编程，如：访问WiFi，访问Android联网信息，邮件等功能。这里不详细讲。