使用系统自带的下载功能

package com.hebaijun.downloadtest;

import java.io.File;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;

import android.app.Activity;
import android.app.DownloadManager;
import android.app.DownloadManager.Request;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.preference.PreferenceManager;
import android.util.Log;
import android.webkit.MimeTypeMap;

public class DownloadTestActivity extends Activity {
    private DownloadManager downloadManager;
    private SharedPreferences prefs;
    private static final String DL_ID = "downloadI24d3222222";
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        downloadManager = (DownloadManager)getSystemService(DOWNLOAD_SERVICE);
        prefs = PreferenceManager.getDefaultSharedPreferences(this); 
    }
    @Override
    protected void onPause() {
        // TODO Auto-generated method stub
        super.onPause();
        unregisterReceiver(receiver);
    }
    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();
        if(!prefs.contains(DL_ID)) { 
            String url = "http://down.angeeks.com/c/d2/d10129/10129003.apk";
            //开始下载 
            Uri resource = Uri.parse(encodeGB(url)); 
            DownloadManager.Request request = new DownloadManager.Request(resource); 
            request.setAllowedNetworkTypes(Request.NETWORK_MOBILE | Request.NETWORK_WIFI); 
            request.setAllowedOverRoaming(false); 
            //设置文件类型
            MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
            String mimeString = mimeTypeMap.getMimeTypeFromExtension(MimeTypeMap.getFileExtensionFromUrl(url));
            request.setMimeType(mimeString);
            //在通知栏中显示 
            request.setShowRunningNotification(true);
            request.setVisibleInDownloadsUi(true);
            //sdcard的目录下的download文件夹
            request.setDestinationInExternalPublicDir("/download/", "G5223.apk");
            request.setTitle("移动G3广告"); 
            long id = downloadManager.enqueue(request); 
            //保存id 
            prefs.edit().putLong(DL_ID, id).commit(); 
        } else { 
            //下载已经开始，检查状态
            queryDownloadStatus(); 
        } 

        registerReceiver(receiver, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
    }
    
    /**
     * 如果服务器不支持中文路径的情况下需要转换url的编码。
     * @param string
     * @return
     */
    public String encodeGB(String string)
    {
        //转换中文编码
        String split[] = string.split("/");
        for (int i = 1; i < split.length; i++) {
            try {
                split[i] = URLEncoder.encode(split[i], "GB2312");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            split[0] = split[0]+"/"+split[i];
        }
        split[0] = split[0].replaceAll("\\+", "%20");//处理空格
        return split[0];
    }
    
    private BroadcastReceiver receiver = new BroadcastReceiver() { 
        @Override 
        public void onReceive(Context context, Intent intent) { 
            //这里可以取得下载的id，这样就可以知道哪个文件下载完成了。适用与多个下载任务的监听
            Log.v("intent", ""+intent.getLongExtra(DownloadManager.EXTRA_DOWNLOAD_ID, 0));
            queryDownloadStatus(); 
        } 
    }; 
    
    private void queryDownloadStatus() { 
        DownloadManager.Query query = new DownloadManager.Query(); 
        query.setFilterById(prefs.getLong(DL_ID, 0)); 
        Cursor c = downloadManager.query(query); 
        if(c.moveToFirst()) { 
            int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS)); 
            switch(status) { 
            case DownloadManager.STATUS_PAUSED: 
                Log.v("down", "STATUS_PAUSED");
            case DownloadManager.STATUS_PENDING: 
                Log.v("down", "STATUS_PENDING");
            case DownloadManager.STATUS_RUNNING: 
                //正在下载，不做任何事情
                Log.v("down", "STATUS_RUNNING");
                break; 
            case DownloadManager.STATUS_SUCCESSFUL: 
                //完成
                Log.v("down", "下载完成");
                Intent intent = new Intent(Intent.ACTION_VIEW);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                String installPath = Environment.getExternalStorageDirectory()+ "/download/G5223.apk";
                intent.setDataAndType(Uri.fromFile(new File(installPath)),"application/vnd.android.package-archive");
                startActivity(intent);
                break; 
            case DownloadManager.STATUS_FAILED: 
                //清除已下载的内容，重新下载
                Log.v("down", "STATUS_FAILED");
                downloadManager.remove(prefs.getLong(DL_ID, 0)); 
                prefs.edit().clear().commit(); 
                break; 
            } 
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hebaijun.downloadtest"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="8" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".DownloadTestActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION"/>
</manifest>