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：

[java] view plaincopy

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。