android实现断点续传

代码如下:

package com.example.downloaderstopsart;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.StrictMode;
import android.app.ListActivity;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends ListActivity  {

         // 固定下载的资源路径，这里可以设置网络上的地址
          private static final String URL = "http://10.81.36.193:8080/";
          // 固定存放下载的音乐的路径：SD卡目录下
          private static final String SD_PATH = "/mnt/sdcard/";
          // 存放各个下载器
          private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();
          // 存放与下载器对应的进度条
          private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();
          /**
           * 利用消息处理机制适时更新进度条
           */
          private Handler mHandler = new Handler() {
              public void handleMessage(Message msg) {
                  if (msg.what == 1) {
                      String url = (String) msg.obj;
                      int length = msg.arg1;
                      ProgressBar bar = ProgressBars.get(url);
                      if (bar != null) {
                          // 设置进度条按读取的length长度更新
                          bar.incrementProgressBy(length);
                          if (bar.getProgress() == bar.getMax()) {
                              Toast.makeText(MainActivity.this, "下载完成！", 0).show();
                              // 下载完成后清除进度条并将map中的数据清空
                              LinearLayout layout = (LinearLayout) bar.getParent();
                              layout.removeView(bar);
                              ProgressBars.remove(url);
                              downloaders.get(url).delete(url);
                              downloaders.get(url).reset();
                              downloaders.remove(url);
                          }
                      }
                  }
              }
          };
          @Override
          public void onCreate(Bundle savedInstanceState) {
              super.onCreate(savedInstanceState);
              setContentView(R.layout.activity_main);
              showListView();
              StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().detectDiskWrites().detectNetwork().penaltyLog().build());
              StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder().detectLeakedSqlLiteObjects().detectLeakedClosableObjects().penaltyLog().penaltyDeath().build());
          }
          // 显示listView，这里可以随便添加音乐
          private void showListView() {
              List<Map<String, String>> data = new ArrayList<Map<String, String>>();
              Map<String, String> map = new HashMap<String, String>();
              map.put("name", "mm.mp3");
              data.add(map);
              map = new HashMap<String, String>();
              map.put("name", "pp.mp3");
              data.add(map);
              map = new HashMap<String, String>();
              map.put("name", "tt.mp3");
              data.add(map);
              map = new HashMap<String, String>();
              map.put("name", "ou.mp3");
              data.add(map);
              SimpleAdapter adapter = new SimpleAdapter(this, data, R.layout.list_item, new String[] { "name" },
                      new int[] { R.id.tv_resouce_name });
              setListAdapter(adapter);
          }
          /**
           * 响应开始下载按钮的点击事件
           */
          public void startDownload(View v) {
              // 得到textView的内容
              LinearLayout layout = (LinearLayout) v.getParent();
              String musicName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
              String urlstr = URL + musicName;
              String localfile = SD_PATH + musicName;
              //设置下载线程数为4，这里是我为了方便随便固定的
              int threadcount = 4;
              // 初始化一个downloader下载器
              Downloader downloader = downloaders.get(urlstr);
              if (downloader == null) {
                  downloader = new Downloader(urlstr, localfile, threadcount, this, mHandler);
                  downloaders.put(urlstr, downloader);
              }
              if (downloader.isdownloading())
                 return;
             // 得到下载信息类的个数组成集合
             LoadInfo loadInfo = downloader.getDownloaderInfors();
             // 显示进度条
             showProgress(loadInfo, urlstr, v);
             // 调用方法开始下载
             downloader.download();
         }

         /**
          * 显示进度条
          */
         private void showProgress(LoadInfo loadInfo, String url, View v) {
             ProgressBar bar = ProgressBars.get(url);
             if (bar == null) {
                 bar = new ProgressBar(this, null, android.R.attr.progressBarStyleHorizontal);
                 bar.setMax(loadInfo.getFileSize());
                 bar.setProgress(loadInfo.getComplete());
                 ProgressBars.put(url, bar);
                 LinearLayout.LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, 5);
                 ((LinearLayout) ((LinearLayout) v.getParent()).getParent()).addView(bar, params);
             }
         }
         /**
          * 响应暂停下载按钮的点击事件
          */
         public void pauseDownload(View v) {
             LinearLayout layout = (LinearLayout) v.getParent();
             String musicName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();
             String urlstr = URL + musicName;
             downloaders.get(urlstr).pause();
         }
     }

DBHelper：

package com.example.downloaderstopsart;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * 建立一个数据库帮助类
 */
public class DBHelper extends SQLiteOpenHelper {
    // download.db-->数据库名
    public DBHelper(Context context) {
        super(context, "download.db", null, 1);
    }

    /**
     * 在download.db数据库下创建一个download_info表存储下载信息
     */
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "
                + "start_pos integer, end_pos integer, compelete_size integer,url char)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

}

DownloadInfo：

package com.example.downloaderstopsart;

public class DownloadInfo {
    private int threadId;// 下载器id
    private int startPos;// 开始点
    private int endPos;// 结束点
    private int compeleteSize;// 完成度
    private String url;// 下载器网络标识

    public DownloadInfo(int threadId, int startPos, int endPos,
            int compeleteSize, String url) {
        this.threadId = threadId;
        this.startPos = startPos;
        this.endPos = endPos;
        this.compeleteSize = compeleteSize;
        this.url = url;
    }

    public DownloadInfo() {
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public int getThreadId() {
        return threadId;
    }

    public void setThreadId(int threadId) {
        this.threadId = threadId;
    }

    public int getStartPos() {
        return startPos;
    }

    public void setStartPos(int startPos) {
        this.startPos = startPos;
    }

    public int getEndPos() {
        return endPos;
    }

    public void setEndPos(int endPos) {
        this.endPos = endPos;
    }

    public int getCompeleteSize() {
        return compeleteSize;
    }

    public void setCompeleteSize(int compeleteSize) {
        this.compeleteSize = compeleteSize;
    }

    @Override
    public String toString() {
        return "DownloadInfo [threadId=" + threadId + ", startPos=" + startPos
                + ", endPos=" + endPos + ", compeleteSize=" + compeleteSize
                + "]";
    }
}

LoadInfo：

package com.example.downloaderstopsart;

public class LoadInfo {
    public int fileSize;// 文件大小
    private int complete;// 完成度
    private String urlstring;// 下载器标识

    public LoadInfo(int fileSize, int complete, String urlstring) {
        this.fileSize = fileSize;
        this.complete = complete;
        this.urlstring = urlstring;
    }

    public LoadInfo() {
    }

    public int getFileSize() {
        return fileSize;
    }

    public void setFileSize(int fileSize) {
        this.fileSize = fileSize;
    }

    public int getComplete() {
        return complete;
    }

    public void setComplete(int complete) {
        this.complete = complete;
    }

    public String getUrlstring() {
        return urlstring;
    }

    public void setUrlstring(String urlstring) {
        this.urlstring = urlstring;
    }

    @Override
    public String toString() {
        return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete
                + ", urlstring=" + urlstring + "]";
    }
}

Downloader：

package com.example.downloaderstopsart;
import java.io.File;
import java.io.InputStream;
 import java.io.RandomAccessFile;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;
 import android.content.Context;
 import android.os.Handler;
 import android.os.Message;
 import android.util.Log;

 public class Downloader {
     private String urlstr;// 下载的地址
     private String localfile;// 保存路径
     private int threadcount;// 线程数
     private Handler mHandler;// 消息处理器
     private Dao dao;// 工具类
     private int fileSize;// 所要下载的文件的大小
     private List<DownloadInfo> infos;// 存放下载信息类的集合
     private static final int INIT = 1;//定义三种下载的状态：初始化状态，正在下载状态，暂停状态
     private static final int DOWNLOADING = 2;
     private static final int PAUSE = 3;
     private int state = INIT;

     public Downloader(String urlstr, String localfile, int threadcount,
             Context context, Handler mHandler) {
         this.urlstr = urlstr;
         this.localfile = localfile;
         this.threadcount = threadcount;
         this.mHandler = mHandler;
         dao = new Dao(context);
     }
     /**
      *判断是否正在下载
      */
     public boolean isdownloading() {
         return state == DOWNLOADING;
     }
     /**
      * 得到downloader里的信息
      * 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中
      * 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器
      */
     public LoadInfo getDownloaderInfors() {
         if (isFirst(urlstr)) {
             Log.v("TAG", "isFirst");
             init();
             int range = fileSize / threadcount;
             infos = new ArrayList<DownloadInfo>();
             for (int i = 0; i < threadcount - 1; i++) {
                 DownloadInfo info = new DownloadInfo(i, i * range, (i + 1)* range - 1, 0, urlstr);
                 infos.add(info);
             }
             DownloadInfo info = new DownloadInfo(threadcount - 1,(threadcount - 1) * range, fileSize - 1, 0, urlstr);
             infos.add(info);
             //保存infos中的数据到数据库
             dao.saveInfos(infos);
             //创建一个LoadInfo对象记载下载器的具体信息
             LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);
             return loadInfo;
         } else {
             //得到数据库中已有的urlstr的下载器的具体信息
             infos = dao.getInfos(urlstr);
             Log.v("TAG", "not isFirst size=" + infos.size());
             int size = 0;
             int compeleteSize = 0;
             for (DownloadInfo info : infos) {
                 compeleteSize += info.getCompeleteSize();
                 size += info.getEndPos() - info.getStartPos() + 1;
             }
             return new LoadInfo(size, compeleteSize, urlstr);
         }
     }

     /**
      * 初始化
      */
     private void init() {
         try {
             URL url = new URL(urlstr);
             HttpURLConnection connection = (HttpURLConnection) url.openConnection();
             connection.setConnectTimeout(5000);
             connection.setRequestMethod("GET");
             fileSize = connection.getContentLength();

             File file = new File(localfile);
             if (!file.exists()) {
                 file.createNewFile();
             }
             // 本地访问文件
             RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
             accessFile.setLength(fileSize);
             accessFile.close();
             connection.disconnect();
         } catch (Exception e) {
             e.printStackTrace();
         }
     }

     /**
      * 判断是否是第一次 下载
      */
     private boolean isFirst(String urlstr) {
         return dao.isHasInfors(urlstr);
     }

     /**
      * 利用线程开始下载数据
      */
     public void download() {
         if (infos != null) {
             if (state == DOWNLOADING)
                 return;
             state = DOWNLOADING;
             for (DownloadInfo info : infos) {
                 new MyThread(info.getThreadId(), info.getStartPos(),
                         info.getEndPos(), info.getCompeleteSize(),
                         info.getUrl()).start();
             }
         }
     }

     public class MyThread extends Thread {
         private int threadId;
         private int startPos;
         private int endPos;
         private int compeleteSize;
         private String urlstr;

         public MyThread(int threadId, int startPos, int endPos,
                 int compeleteSize, String urlstr) {
             this.threadId = threadId;
             this.startPos = startPos;
             this.endPos = endPos;
             this.compeleteSize = compeleteSize;
             this.urlstr = urlstr;
         }
         @Override
         public void run() {
             HttpURLConnection connection = null;
             RandomAccessFile randomAccessFile = null;
             InputStream is = null;
             try {

                 URL url = new URL(urlstr);
                 connection = (HttpURLConnection) url.openConnection();
                 connection.setConnectTimeout(5000);
                 connection.setRequestMethod("GET");
                 // 设置范围，格式为Range：bytes x-y;
                 connection.setRequestProperty("Range", "bytes="+(startPos + compeleteSize) + "-" + endPos);

                 randomAccessFile = new RandomAccessFile(localfile, "rwd");
                 randomAccessFile.seek(startPos + compeleteSize);
                 Log.i("RG", "connection--->>>"+connection);
                 // 将要下载的文件写到保存在保存路径下的文件中
                 is = connection.getInputStream();
                 byte[] buffer = new byte[4096];
                 int length = -1;
                 while ((length = is.read(buffer)) != -1) {
                     randomAccessFile.write(buffer, 0, length);
                     compeleteSize += length;
                     // 更新数据库中的下载信息
                     dao.updataInfos(threadId, compeleteSize, urlstr);
                     // 用消息将下载信息传给进度条，对进度条进行更新
                     Message message = Message.obtain();
                     message.what = 1;
                     message.obj = urlstr;
                     message.arg1 = length;
                     mHandler.sendMessage(message);
                     if (state == PAUSE) {
                         return;
                     }
                 }
             } catch (Exception e) {
                 e.printStackTrace();
             } finally {
                 try {
                     is.close();
                     randomAccessFile.close();
                     connection.disconnect();
                     dao.closeDb();
                 } catch (Exception e) {
                     e.printStackTrace();
                 }
             }

         }
     }
     //删除数据库中urlstr对应的下载器信息
     public void delete(String urlstr) {
         dao.delete(urlstr);
     }
     //设置暂停
     public void pause() {
         state = PAUSE;
     }
     //重置下载状态
     public void reset() {
        state = INIT;
     }
 }

Dao:

package com.example.downloaderstopsart;

import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

public class Dao {
    private DBHelper dbHelper;

    public Dao(Context context) {
        dbHelper = new DBHelper(context);
    }

    /**
     * 查看数据库中是否有数据
     */
    public boolean isHasInfors(String urlstr) {
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        String sql = "select count(*)  from download_info where url=?";
        Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
        cursor.moveToFirst();
        int count = cursor.getInt(0);
        cursor.close();
        return count == 0;
    }

    /**
     * 36 * 保存 下载的具体信息 37
     */
    public void saveInfos(List<DownloadInfo> infos) {
        SQLiteDatabase database = dbHelper.getWritableDatabase();
        for (DownloadInfo info : infos) {
            String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";
            Object[] bindArgs = { info.getThreadId(), info.getStartPos(),
                    info.getEndPos(), info.getCompeleteSize(), info.getUrl() };
            database.execSQL(sql, bindArgs);
        }
    }

    /**
     * 得到下载具体信息
     */
    public List<DownloadInfo> getInfos(String urlstr) {
        List<DownloadInfo> list = new ArrayList<DownloadInfo>();
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
        Cursor cursor = database.rawQuery(sql, new String[] { urlstr });
        while (cursor.moveToNext()) {
            DownloadInfo info = new DownloadInfo(cursor.getInt(0),
                    cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),
                    cursor.getString(4));
            list.add(info);
        }
        cursor.close();
        return list;
    }

    /**
     * 更新数据库中的下载信息
     */
    public void updataInfos(int threadId, int compeleteSize, String urlstr) {
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        String sql = "update download_info set compelete_size=? where thread_id=? and url=?";
        Object[] bindArgs = { compeleteSize, threadId, urlstr };
        database.execSQL(sql, bindArgs);
    }

    /**
     * 关闭数据库
     */
    public void closeDb() {
        dbHelper.close();
    }

    /**
     * 下载完成后删除数据库中的数据
     */
    public void delete(String url) {
        SQLiteDatabase database = dbHelper.getReadableDatabase();
        database.delete("download_info", "url=?", new String[] { url });
        database.close();
    }
}

xml如下：

<?xml version="1.0" encoding="utf-8"?>
  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:orientation="vertical"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:id="@+id/llRoot">
      <ListView android:id="@android:id/list"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent">
     </ListView>
 </LinearLayout>

item_list.xml：

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

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="5dip"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/tv_resouce_name"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1" />

        <Button
            android:id="@+id/btn_start"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="startDownload"
            android:text="下载" />

        <Button
            android:id="@+id/btn_pause"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="pauseDownload"
            android:text="暂停" />
    </LinearLayout>

</LinearLayout>

记得加权限：

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

还有在3.0以上的版本记得加上这句话：

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().detectDiskWrites().detectNetwork().penaltyLog().build());
          StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder().detectLeakedSqlLiteObjects().detectLeakedClosableObjects().penaltyLog().penaltyDeath().build());

效果图如下：