Android的网络通信的方式有两种：
- Socket
- HTTP
而其中，HTTP又包括两种编程方式：
- HttpURLConnection
- HttpClient
这篇文章介绍的就是，HttpURLConnection
首先，当然是创建HttpURLConnection的对象
URL url = new URL("www.baidu.com"); HttpURLConnection connection=(HttpURLConnection)url.openConnection(); 第二步是设置，其中最重要的就是 GET or POST？（GET是从服务器读取数据，POST是提交数据给服务器）
connection.setRequestMethod("GET");
connection.setConnectTimeout(8000);//连接超时
connection.setReadTimeout(8000);//读取超时
接着，就可以从connection中获取数据了
InputStream in = connection.getInputStream();
最后需要关闭连接
connection.disconnect();
例子
要访问网络，所以需要在清单文件里添加权限：
<uses-permission android:name="android.permission.INTERNET"/>
MainActivity.java
public class MainActivity extends Activity implements OnClickListener { private Button sendRequest; private TextView responseText; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); sendRequest = (Button) findViewById(R.id.send_request); responseText = (TextView) findViewById(R.id.response); sendRequest.setOnClickListener(this); } @Override public void onClick(View v) { // TODO Auto-generated method stub if (v.getId() == R.id.send_request) { sendRequestWithHttpURLConnection(); } } private void sendRequestWithHttpURLConnection() { new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub HttpURLConnection connection = null; try { URL url = new URL("www.baidu.com"); connection = (HttpURLConnection) url.openConnection(); connection.setConnectTimeout(8000); connection.setReadTimeout(8000); connection.setRequestMethod("GET"); String line = null; StringBuilder response = new StringBuilder(); InputStream in = connection.getInputStream(); BufferedReader reader = new BufferedReader( new InputStreamReader(in)); while ((line = reader.readLine()) != null) { response.append(line); Log.e("MainActivity", line); } responseText.setText(response.toString()); } catch (Exception e) { e.printStackTrace(); } finally { if (connection != null) connection.disconnect(); } } }).start(); }}上面代码的逻辑很简单，就是：点击“发送”按钮，从百度首页获取数据，并显示在文本框里。
但这里有两个问题需要注意：
- 写网址，也就是URL时，需要加上协议名，也就是"http://"
- 上面的代码如果真的运行，文本框里是不会显示任何内容的，因为子线程中无法对 UI 进行操作
第一个问题容易解决，加上http://就行了。
而第二个问题，解决的办法是：创建一个Message对象，使用Handler把它发送出去，在Handler的方法里来处理这条Message。
修改后的代码
public class MainActivity extends Activity implements OnClickListener { private Button sendRequest; private TextView responseText; public static final int SHOW_RESPONSE = 0; private Handler handler = new Handler(){ public void handleMessage(Message msg){ switch (msg.what) { case SHOW_RESPONSE: String response = (String)msg.obj; responseText.setText(response); break; default: break; } } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); sendRequest = (Button) findViewById(R.id.send_request); responseText = (TextView) findViewById(R.id.response); sendRequest.setOnClickListener(this); } @Override public void onClick(View v) { // TODO Auto-generated method stub if (v.getId() == R.id.send_request) { sendRequestWithHttpURLConnection(); } } private void sendRequestWithHttpURLConnection() { new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub HttpURLConnection connection = null; try { URL url = new URL("http://www.baidu.com"); connection = (HttpURLConnection) url.openConnection(); connection.setConnectTimeout(8000); connection.setReadTimeout(8000); connection.setRequestMethod("GET"); String line = null; StringBuilder response = new StringBuilder(); InputStream in = connection.getInputStream(); BufferedReader reader = new BufferedReader( new InputStreamReader(in)); while ((line = reader.readLine()) != null) { response.append(line); Log.e("MainActivity", line); } Message message = new Message(); message.what = SHOW_RESPONSE; message.obj = response.toString(); handler.sendMessage(message); } catch (Exception e) { e.printStackTrace(); } finally { if (connection != null) connection.disconnect(); } } }).start(); }}如果在本机上开了Tomcat服务器，那么URL里的内容就可以是http://192.168.0.100:8080
这样，点击按钮后，就能在文本框里显示本机里的这个URL的内容了。