谈谈Android的三种网络通信方式

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。

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