讲到http就必需要了解URI和URL

URI (uniform resource identifier)统一资源标志符；
URL(uniform resource location )统一资源定位符（或统一资源定位器）；

可以理解成URL是URI的子集，URI是一抽象的标识符，URL可以理解成具体的标识符；只要是网络上的资源就能找到唯一的URL。

目录结构

效果图

关键代码

HttpUtils.java类

package com.dzt.downloadimage.utils;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

/**
 * http工具类 http可以使用HttpURLConnection或HttpClient
 * 
 * @author Administrator
 * @date 2014.05.10
 * @version V1.0
 */
public class HttpUtils {

	/**
	 * 获取网络图片
	 * 
	 * @param urlString
	 *            如：http://f.hiphotos.baidu.com/image/w%3D2048/sign=3
	 *            b06d28fc91349547e1eef6462769358
	 *            /d000baa1cd11728b22c9e62ccafcc3cec2fd2cd3.jpg
	 * @return
	 * @date 2014.05.10
	 */
	public static Bitmap getNetWorkBitmap(String urlString) {
		URL imgUrl = null;
		Bitmap bitmap = null;
		try {
			imgUrl = new URL(urlString);
			// 使用HttpURLConnection打开连接
			HttpURLConnection urlConn = (HttpURLConnection) imgUrl
					.openConnection();
			urlConn.setDoInput(true);
			urlConn.connect();
			// 将得到的数据转化成InputStream
			InputStream is = urlConn.getInputStream();
			// 将InputStream转换成Bitmap
			bitmap = BitmapFactory.decodeStream(is);
			is.close();
		} catch (MalformedURLException e) {
			// TODO Auto-generated catch block
			System.out.println("[getNetWorkBitmap->]MalformedURLException");
			e.printStackTrace();
		} catch (IOException e) {
			System.out.println("[getNetWorkBitmap->]IOException");
			e.printStackTrace();
		}
		return bitmap;
	}
}

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

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]);
			mDownloadImage = HttpUtils.getNetWorkBitmap(params[0]);
			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);
		}

	}