使用Http协议访问网络--HttpClient

最新推荐文章于 2020-06-29 19:09:22 发布

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最新推荐文章于 2020-06-29 19:09:22 发布

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本文链接：https://blog.youkuaiyun.com/DouDouLee_blog/article/details/51740965

本文介绍如何使用Apache HttpClient发起HTTP GET请求并处理响应。主要内容包括创建HttpClient实例、构造HttpGet对象、执行请求、处理响应状态码及内容，并通过Handler机制更新UI。

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public interface

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(){
		@Override
		public 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(){
		@Override
		public void handleMessage(Message msg){
			if(msg.what == SEND_REQUEST){
				String response = (String)msg.obj;
				responseTextView.setText(response);
			}
		}
	};
	@Override
	protected 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);
		
	}
	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		if(v.getId() == R.id.requestBtn){
			sendRequestWithHttpClient();
		}
	}

	private void sendRequestWithHttpClient(){
		new Thread(new Runnable(){
			@Override
			public 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();
	}
	
}