在前一章中讲的是Android使用HttpURLConnection下载图片，这一章使用HttpClient下载图片

HttpURLConnection与HttpClient的区别：

HttpClient是个很不错的开源框架（org.appache.http），封装了访问http的请求头，参数，内容体，响应等等，使用起来更方面更强大。
HttpURLConnection是java的标准类，可以实现简单的基于URL请求、响应功能，什么都没封装，用起来太原始，比如重访问的自定义，以及一些高级功能等。

还是在上一章的基础上添加HttpClient

关键下载代码

/**
	 * 通过Get获取网页内容
	 * 
	 * @param url
	 *            如：http://preview.quanjing.com/is002/ev601-025.jpg
	 * @return
	 * @throws ClientProtocolException
	 * @throws IOException
	 * @date 2014.05.10
	 */
	public static Bitmap getHttpGetBitmap(String url)
			throws ClientProtocolException, IOException {
		Bitmap bitmap = null;
		// 新建一个默认的连接
		HttpClient client = new DefaultHttpClient();
		// 新建一个Get方法
		HttpGet get = new HttpGet(url);
		// 得到网络的回应
		HttpResponse response = client.execute(get);

		// 如果服务器响应的是OK的话！
		if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {
			InputStream is = response.getEntity().getContent();
			bitmap = BitmapFactory.decodeStream(is);
			is.close();
		}
		return bitmap;
	}

访问互联网权限

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

package com.dzt.downloadimage;

import java.io.IOException;
import java.net.MalformedURLException;

import org.apache.http.client.ClientProtocolException;

import android.app.Activity;
import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

import com.dzt.downloadimage.utils.HttpUtils;

public class MainActivity extends Activity implements OnClickListener {

	private Bitmap mDownloadImage = null;
	private ImageView image = null;
	private downloadImageTask task;
	private boolean _isExe = false;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		initWidgets();
		task = new downloadImageTask();
	}

	@Override
	protected void onStop() {
		// TODO Auto-generated method stub
		super.onStop();
		if (_isExe) {
			task.cancel(true); // 取消操作
		}
	}

	private void initWidgets() {
		image = (ImageView) findViewById(R.id.img);
		Button btn = (Button) findViewById(R.id.download_btn);
		btn.setOnClickListener(this);
	}

	@Override
	public void onClick(View v) {
		// TODO Auto-generated method stub
		switch (v.getId()) {
		case R.id.download_btn:
			if (!_isExe) {
				task.execute("http://preview.quanjing.com/is002/ev601-025.jpg"); // 执行异步操作
				_isExe = true;
			}
			break;

		default:
			break;
		}
	}

	class downloadImageTask extends AsyncTask<String, Integer, Boolean> {

		@Override
		protected Boolean doInBackground(String... params) {
			// TODO Auto-generated method stub
			System.out.println("[downloadImageTask->]doInBackground "
					+ params[0]);
			// try {
			// mDownloadImage = HttpUtils.getNetWorkBitmap(params[0]);
			// } catch (MalformedURLException e) {
			// // TODO Auto-generated catch block
			// e.printStackTrace();
			// } catch (IOException e) {
			// // TODO Auto-generated catch block
			// e.printStackTrace();
			// }
			try {
				mDownloadImage = HttpUtils.getHttpGetBitmap(params[0]);
			} catch (ClientProtocolException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			return true;
		}

		// 下载完成回调
		@Override
		protected void onPostExecute(Boolean result) {
			// TODO Auto-generated method stub
			image.setImageBitmap(mDownloadImage);
			System.out.println("result = " + result);
			super.onPostExecute(result);
		}

		// 更新进度回调
		@Override
		protected void onProgressUpdate(Integer... values) {
			// TODO Auto-generated method stub
			super.onProgressUpdate(values);
		}

	}
}