HttpClient

org.apache.http.client.HttpClient

HttpClient是Apache提供的Http网络访问接口。

1、创建HttpClient实例

HttpClient是一个接口，无法直接创建实例，通常创建一个DefaultHttpClient（HttpClient 的SubClass）实例。

HttpClient httpClient = new DefaultHttpClient();

2、如果想要发起一条GET请求 ,可以创建一个HttpGet对象，传入目标地址，之后调用HttpClient的execute()方法

HttpGet = new HttpClient("http://www.baidu.com");
httpClient.execute(httpGet);

3、执行execute()后，会返回一个HttpResponse对象，服务器返回的所有信息都在这里面，通常都会先取出服务器返回的状态吗，若等于200则说明请求和相应都成功了

if(httpResponse.getStatusLine().getStatusCode() == 200){
}

接下来在这个if判断内部取出服务返回的具体内容，可以调用httpResponse getEntity()获得一个HttpEntity实例，再调用EntityUtils.toString这个静态方法将HttpEntity转换成字符串

HttpEntity httpEntity = httpResponse.getEntity();
String responseString = EntityUtils.toString(httpEntity,"utf-8");

由于在子线程中无法对UI操作，最后使用Message，将服务器返回的数据放到Message对象中，用Handler将messge发送出去，在主线程进行UI操作

//将服务器返回的结果存放到Message对象中
Message message = Message.obtain(mHandler, SEND_REQUEST, responseString);
mHandler.sendMessage(message);

Handler mHandler = new Handler(){@Overridepublic void handleMessage(Message msg){if(msg.what == SEND_REQUEST){String response = (String)msg.obj;responseTextView.setText(response);}}};

主要代码：

public class MainActivity extends ActionBarActivity implements OnClickListener{private Button sendRequestBtn;private TextView responseTextView;private int SEND_REQUEST = 0;Handler mHandler = new Handler(){@Overridepublic void handleMessage(Message msg){if(msg.what == SEND_REQUEST){String response = (String)msg.obj;responseTextView.setText(response);}}};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);sendRequestBtn = (Button)findViewById(R.id.requestBtn);responseTextView = (TextView)findViewById(R.id.responseText);sendRequestBtn.setOnClickListener(this);}@Overridepublic void onClick(View v) {// TODO Auto-generated method stubif(v.getId() == R.id.requestBtn){sendRequestWithHttpClient();}}private void sendRequestWithHttpClient(){new Thread(new Runnable(){@Overridepublic void run(){try{HttpClient httpClient = new DefaultHttpClient();HttpGet httpGet= new HttpGet("http://www.baidu.com");HttpResponse httpResponse = httpClient.execute(httpGet);if(httpResponse.getStatusLine().getStatusCode() == 200){//获得消息的响应实体HttpEntity httpEntity = httpResponse.getEntity();String responseString = EntityUtils.toString(httpEntity,"utf-8");//将服务器返回的结果存放到Message对象中Message message = Message.obtain(mHandler, SEND_REQUEST, responseString);mHandler.sendMessage(message);}}catch(Exception e){e.printStackTrace();}}}).start();}}