简单使用URLConnection、HttpURLConnection和HttpClient访问网络资源

URL的openConnection方法将返回一个URLConnection，该对象表示应用程序和URL之间的通信连接。程序可以通过它的实例向该URL发送请求，读取URL引用的资源。

下面通过一个简单示例来演示：

Activity：

package com.home.urlconnection;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener {
	private Button urlConnectionBtn;
	private Button httpUrlConnectionBtn;
	private Button httpClientBtn;
	private TextView showTextView;
	private WebView webView;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		init();
	}

	private void init() {
		urlConnectionBtn = (Button) findViewById(R.id.test_url_main_btn_urlconnection);
		httpUrlConnectionBtn = (Button) findViewById(R.id.test_url_main_btn_httpurlconnection);
		httpClientBtn = (Button) findViewById(R.id.test_url_main_btn_httpclient);
		showTextView = (TextView) findViewById(R.id.test_url_main_tv_show);
		webView = (WebView) findViewById(R.id.test_url_main_wv);
		urlConnectionBtn.setOnClickListener(this);
		httpUrlConnectionBtn.setOnClickListener(this);
		httpClientBtn.setOnClickListener(this);
	}

	@Override
	public void onClick(View v) {
		if (v == urlConnectionBtn) {
			try {
				// 直接使用URLConnection对象进行连接
				URL url = new URL("http://192.168.1.100:8080/myweb/hello.jsp");
				// 得到URLConnection对象
				URLConnection connection = url.openConnection();
				InputStream is = connection.getInputStream();
				byte[] bs = new byte[1024];
				int len = 0;
				StringBuffer sb = new StringBuffer();
				while ((len = is.read(bs)) != -1) {
					String str = new String(bs, 0, len);
					sb.append(str);
				}
				showTextView.setText(sb.toString());
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		if (v == httpUrlConnectionBtn) {
			// 直接使用HttpURLConnection对象进行连接
			try {
				URL url = new URL(
						"http://192.168.1.100:8080/myweb/hello.jsp?username=abc");
				// 得到HttpURLConnection对象
				HttpURLConnection connection = (HttpURLConnection) url
						.openConnection();
				// 设置为GET方式
				connection.setRequestMethod("GET");
				if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
					// 得到响应消息
					String message = connection.getResponseMessage();
					showTextView.setText(message);
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		if (v == httpClientBtn) {
			try {
				// 使用ApacheHttp客户端进行连接(重要方法)
				HttpClient client = new DefaultHttpClient();

				// 如果是Get提交则创建HttpGet对象，否则创建HttpPost对象
				// POST提交的方式
				HttpPost httpPost = new HttpPost(
						"http://192.168.1.100:8080/myweb/hello.jsp");
				// 如果是Post提交可以将参数封装到集合中传递
				List dataList = new ArrayList();
				dataList.add(new BasicNameValuePair("username", "abc"));
				dataList.add(new BasicNameValuePair("pwd", "123"));
				// UrlEncodedFormEntity用于将集合转换为Entity对象
				httpPost.setEntity(new UrlEncodedFormEntity(dataList));

				// GET提交的方式
				// HttpGet httpGet = new
				// HttpGet("http://192.168.1.100:8080/myweb/hello.jsp?username=abc&pwd=321");

				// 获取相应消息
				HttpResponse httpResponse = client.execute(httpPost);
				// 获取消息内容
				HttpEntity entity = httpResponse.getEntity();
				// 把消息对象直接转换为字符串
				String content = EntityUtils.toString(entity);
				// 显示在TextView中
				// showTextView.setText(content);

				// 通过webview来解析网页
				webView.loadDataWithBaseURL(null, content, "text/html",
						"utf-8", null);
				// 直接根据url来进行解析
				// webView.loadUrl(url);
			} catch (ClientProtocolException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

}

上面使用到的url是部署在笔者本机的web应用，这里不再给出，大家可以换成自己的web应用即可。
布局XML：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/test_url_main_btn_urlconnection"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="使用URLConnection连接" />

    <Button
        android:id="@+id/test_url_main_btn_httpurlconnection"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="使用HttpURLConnection连接" />

    <Button
        android:id="@+id/test_url_main_btn_httpclient"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="使用Apache客户端连接" />

    <TextView
        android:id="@+id/test_url_main_tv_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <WebView
        android:id="@+id/test_url_main_wv"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

权限：

 <uses-permission android:name="android.permission.INTERNET" />