在安卓中，可以直接用java的java.net.URL包访问网络下载数据。不同的是，安卓程序需要权限，需要在AndroidManifest.xml文件中声明权限

 <!-- 网络权限 --><uses-permission android:name="android.permission.INTERNET"/><!-- 操作sd卡权限 --><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

不过有个需要注意的是，我使用的是最新的adt安卓开发集成eclipse的安装包，在使用网络服务的时候，处理网络请求的代码，不能在主线程中进行，不然安卓会提示错误。

但是，有些组件设置值，他必须是在主线程的循环中，才可以。

Looper loop = Looper.getMainLooper();
handler = new Handler(loop){@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);switch (msg.what) {case SETTEXT://主线程ui更新text值text.setText(msg.obj.toString());break;}}
};download.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View arg0) {//新线程下载new Thread(new Runnable() {@Overridepublic void run() {//新建一个下载Download load = new Download(url);String value = load.downloadAsString();Message msg = handler.obtainMessage();msg.obj = value;msg.what = SETTEXT;msg.sendToTarget();}}).start();}
});

Download类：

package com.example.org.suju.download;import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;import android.os.Environment;
import android.util.Log;public class Download {/** 连接url */private String urlstr;/** sd卡目录路径 */private String sdcard;/** http连接管理类 */private HttpURLConnection urlcon;public Download(String url){this.urlstr = url;//获取设备sd卡目录this.sdcard = Environment.getExternalStorageDirectory() + "/";urlcon = getConnection();}/** 读取网络文本*/public String downloadAsString(){StringBuilder sb = new StringBuilder();String temp = null;try {InputStream is = urlcon.getInputStream();BufferedReader br = new BufferedReader(new InputStreamReader(is));while ((temp = br.readLine()) != null) {sb.append(temp);}br.close();} catch (Exception e) {e.printStackTrace();}return sb.toString();}/** 获取http连接处理类HttpURLConnection*/private HttpURLConnection getConnection(){URL url;HttpURLConnection urlcon = null;try {url = new URL(urlstr);urlcon = (HttpURLConnection) url.openConnection();} catch (Exception e) {e.printStackTrace();}return urlcon;}/** 获取连接文件长度。*/public int getLength(){return urlcon.getContentLength();}/** 写文件到sd卡 demo* 前提需要设置模拟器sd卡容量，否则会引发EACCES异常* 先创建文件夹，在创建文件*/public int down2sd(String dir, String filename, downhandler handler){StringBuilder sb = new StringBuilder(sdcard).append(dir);File file = new File(sb.toString());if (!file.exists()) {file.mkdirs();//创建文件夹Log.d("log", sb.toString());}//获取文件全名sb.append(filename);file = new File(sb.toString());FileOutputStream fos = null;try {InputStream is = urlcon.getInputStream();//创建文件file.createNewFile();fos = new FileOutputStream(file);byte[] buf = new byte[1024];while ((is.read(buf)) != -1) {fos.write(buf);//同步更新数据handler.setSize(buf.length);}is.close();} catch (Exception e) {return 0;} finally {try {fos.close();} catch (IOException e) {e.printStackTrace();}}return 1;}/** 内部回调接口类*/public abstract class downhandler{public abstract void setSize(int size);}
}

线程下载提示Activity：

用一个线程循环处理网络下载，并使用下载类回调函数，发送处理消息给主线程消息处理方法，同步更新滚动条值。

        @Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.onCreate(savedInstanceState);setContentView(R.layout.download);text = (TextView) findViewById(R.id.label);load = (ProgressBar) findViewById(R.id.load);//获取传递的Intent的Bundle的url键值final String url = getIntent().getExtras().getString("url");final Handler handler = new Handler(){@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);//这里就一条消息int pro = load.getProgress() + msg.arg1;load.setProgress(pro);text.setText(Integer.toString(pro));if (pro >= load.getMax()) {finish();   //结束下载进度框}}};

      new Thread(new Runnable() {@Overridepublic void run() {//另起线程执行下载，安卓最新sdk规范，网络操作不能再主线程。Download l = new Download(url);load.setMax(l.getLength());/*** 下载文件到sd卡，虚拟设备必须要开始设置sd卡容量* downhandler是Download的内部类，作为回调接口实时显示下载数据*/int status = l.down2sd("downtemp/", "1.ddd", l.new downhandler() {@Overridepublic void setSize(int size) {Message msg = handler.obtainMessage();msg.arg1 = size;msg.sendToTarget();Log.d("log", Integer.toString(size));}});//log输出Log.d("log", Integer.toString(status));}}).start();}

对话框模式的Activity需要设置一个属性android:theme。

<activity
android:name="com.example.org.suju.download.DownloadActivity"
android:theme="@android:style/Theme.Dialog"></activity>

使用一个按钮启动下载对话框Activity，并传递数据

down2sd.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View arg0) {Intent intent = new Intent();intent.setClass(MainActivity.this, DownloadActivity.class);Bundle bundle = new Bundle();bundle.putString("url", urlstr.getText().toString());intent.putExtras(bundle);startActivity(intent);}
});