http://blog.csdn.net/smbroe/article/details/42270573

文件下载在App应用中也用到很多，一般版本更新时多要用的文件下载来进行处理，以前也有看过很多大神有过该方面的博客，今天我也自己来实践一下，写的一般，还请大家多提意见，共同进步。主要思路：

1.多线程下载：

首先通过下载总线程数来划分文件的下载区域：利用int range = fileSize / threadCount；得到每一段下载量；每一段的位置是i * range到(i + 1) * rang  - 1，注意最后一段的位置是到filesize - 1；

通过Http协议的Range字段实现下载文件的分段；

通过Java类RandomAccessFile可以实现文件的随机访问，利用seek方法定位的文件的指定位置；

由HttpUrlConnection获取流来进行流的读写，实现文件的存储；

在下载过程中利用Handler来向外传递下载的信息。

2.断点续传：

对于每一个线程利用一个DownloadInfo类来保存下载的信息，每次在下载过程中向数据库更新信息（我也有想过只在下载暂停时进行更新，但那样的话我们的进程被杀掉时信息就无法保存下来）。在进行下载之前去访问数据库是否有记录存在，如果没有执行第一次下载的初始化，如果存在记录但下载文件不存在时，删掉数据库中的记录之后进行第一次下载的初始化，如果有记录且文件存在，则从数据库中取出信息。

实现的效果如图，自己封装的类提供了开始，暂停，删除，以及重新下载的方法。还没来得及将工程穿上CSDN，给大家一个百度云盘的下载地址：http://pan.baidu.com/s/1dD1Xo8T

主要类的结构有：

1）DownloadHttpTool：利用Http协议进行网络下载类

2）DownlaodSqlTool， DownLoadHelper：数据库相关操作类

3）DownloadInfo：下载信息保存类

4）DownloadUtil：封装下载方法并提供对外接口的类

贴一下代码：DownloadInfo类

package com.example.test;
public class DownloadInfo {/*** 保存每个下载线程下载信息类* */private int threadId;// 下载器idprivate int startPos;// 开始点private int endPos;// 结束点private int compeleteSize;// 完成度private String url;// 下载文件的URL地址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;}@Overridepublic String toString() {return "DownloadInfo [threadId=" + threadId + ", startPos=" + startPos+ ", endPos=" + endPos + ", compeleteSize=" + compeleteSize+ "]";}
}

DownLoadHelper类，创建我们的数据库文件

package com.example.test;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/*** 利用数据库来记录下载信息* @author acer*/
public class DownLoadHelper extends SQLiteOpenHelper{private static final String SQL_NAME = "download.db";private static final int DOWNLOAD_VERSION=1;public DownLoadHelper(Context context) {super(context, SQL_NAME, null, DOWNLOAD_VERSION);// TODO Auto-generated constructor stub}/*** 在download.db数据库下创建一个download_info表存储下载信息*/@Overridepublic 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)");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}

DownlaodSqlTool进行数据的插入更新删除等操作

package com.example.test;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
/*** * 数据库操作工具类*/
public class DownlaodSqlTool {private DownLoadHelper dbHelper;public DownlaodSqlTool(Context context) {dbHelper = new DownLoadHelper(context);}/*** 创建下载的具体信息*/public void insertInfos(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.getWritableDatabase();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);}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.getWritableDatabase();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.getWritableDatabase();database.delete("download_info", "url=?", new String[] { url });}
}

DownloadHttpTool进行网络下载的类

package com.example.test;
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 DownloadHttpTool {/*** * 利用Http协议进行多线程下载具体实践类*/private static final String TAG = DownloadHttpTool.class.getSimpleName();private int threadCount;//线程数量private String urlstr;//URL地址private Context mContext;private Handler mHandler;private List<DownloadInfo> downloadInfos;//保存下载信息的类private String localPath;//目录private String fileName;//文件名private int fileSize;private DownlaodSqlTool sqlTool;//文件信息保存的数据库操作类private enum Download_State {Downloading, Pause, Ready;//利用枚举表示下载的三种状态}private Download_State state = Download_State.Ready;//当前下载状态private int globalCompelete = 0;//所有线程下载的总数public DownloadHttpTool(int threadCount, String urlString,String localPath, String fileName, Context context, Handler handler) {super();this.threadCount = threadCount;this.urlstr = urlString;this.localPath = localPath;this.mContext = context;this.mHandler = handler;this.fileName = fileName;sqlTool = new DownlaodSqlTool(mContext);}//在开始下载之前需要调用ready方法进行配置public void ready() {Log.w(TAG, "ready");globalCompelete = 0;downloadInfos = sqlTool.getInfos(urlstr);if (downloadInfos.size() == 0) {initFirst();} else {File file = new File(localPath + "/" + fileName);if (!file.exists()) {sqlTool.delete(urlstr);initFirst();} else {fileSize = downloadInfos.get(downloadInfos.size() - 1).getEndPos();for (DownloadInfo info : downloadInfos) {globalCompelete += info.getCompeleteSize();}Log.w(TAG, "globalCompelete:::" + globalCompelete);}}}public void start() {Log.w(TAG, "start");if (downloadInfos != null) {if (state == Download_State.Downloading) {return;}state = Download_State.Downloading;for (DownloadInfo info : downloadInfos) {Log.v(TAG, "startThread");new DownloadThread(info.getThreadId(), info.getStartPos(),info.getEndPos(), info.getCompeleteSize(),info.getUrl()).start();}}}public void pause() {state = Download_State.Pause;sqlTool.closeDb();}public void delete(){compelete();File file = new File(localPath + "/" + fileName);file.delete();}public void compelete() {sqlTool.delete(urlstr);sqlTool.closeDb();}public int getFileSize() {return fileSize;}public int getCompeleteSize() {return globalCompelete;}//第一次下载初始化private void initFirst() {Log.w(TAG, "initFirst");try {URL url = new URL(urlstr);HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setConnectTimeout(5000);connection.setRequestMethod("GET");fileSize = connection.getContentLength();Log.w(TAG, "fileSize::" + fileSize);File fileParent = new File(localPath);if (!fileParent.exists()) {fileParent.mkdir();}File file = new File(fileParent, fileName);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();}int range = fileSize / threadCount;downloadInfos = new ArrayList<DownloadInfo>();for (int i = 0; i < threadCount - 1; i++) {DownloadInfo info = new DownloadInfo(i, i * range, (i + 1) * range- 1, 0, urlstr);downloadInfos.add(info);}DownloadInfo info = new DownloadInfo(threadCount - 1, (threadCount - 1)* range, fileSize - 1, 0, urlstr);downloadInfos.add(info);sqlTool.insertInfos(downloadInfos);}//自定义下载线程private class DownloadThread extends Thread {private int threadId;private int startPos;private int endPos;private int compeleteSize;private String urlstr;private int totalThreadSize;public DownloadThread(int threadId, int startPos, int endPos,int compeleteSize, String urlstr) {this.threadId = threadId;this.startPos = startPos;this.endPos = endPos;totalThreadSize = endPos - startPos + 1;this.urlstr = urlstr;this.compeleteSize = compeleteSize;}@Overridepublic void run() {HttpURLConnection connection = null;RandomAccessFile randomAccessFile = null;InputStream is = null;try {randomAccessFile = new RandomAccessFile(localPath + "/"+ fileName, "rwd");randomAccessFile.seek(startPos + compeleteSize);URL url = new URL(urlstr);connection = (HttpURLConnection) url.openConnection();connection.setConnectTimeout(5000);connection.setRequestMethod("GET");connection.setRequestProperty("Range", "bytes="+ (startPos + compeleteSize) + "-" + endPos);is = connection.getInputStream();byte[] buffer = new byte[1024];int length = -1;while ((length = is.read(buffer)) != -1) {randomAccessFile.write(buffer, 0, length);compeleteSize += length;Message message = Message.obtain();message.what = threadId;message.obj = urlstr;message.arg1 = length;mHandler.sendMessage(message);sqlTool.updataInfos(threadId, compeleteSize, urlstr);Log.w(TAG, "Threadid::" + threadId + "    compelete::"+ compeleteSize + "    total::" + totalThreadSize);if (compeleteSize >= totalThreadSize) {break;}if (state != Download_State.Downloading) {break;}}} catch (Exception e) {e.printStackTrace();} finally {try {if (is != null) {is.close();}randomAccessFile.close();connection.disconnect();} catch (Exception e) {e.printStackTrace();}}}}
}

DownloadUtils提供下载向外接口方法类：

package com.example.test;
import android.annotation.SuppressLint;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
/*** 将下载方法封装在此类* 提供下载，暂停，删除，以及重置的方法*/
public class DownloadUtil {private DownloadHttpTool mDownloadHttpTool;private OnDownloadListener onDownloadListener;private int fileSize;private int downloadedSize = 0;@SuppressLint("HandlerLeak")private Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubsuper.handleMessage(msg);int length = msg.arg1;synchronized (this) {//加锁保证已下载的正确性downloadedSize += length;}if (onDownloadListener != null) {onDownloadListener.downloadProgress(downloadedSize);}if (downloadedSize >= fileSize) {mDownloadHttpTool.compelete();if (onDownloadListener != null) {onDownloadListener.downloadEnd();}}}};public DownloadUtil(int threadCount, String filePath, String filename,String urlString, Context context) {mDownloadHttpTool = new DownloadHttpTool(threadCount, urlString,filePath, filename, context, mHandler);}//下载之前首先异步线程调用ready方法获得文件大小信息，之后调用开始方法public void start() {new AsyncTask<Void, Void, Void>() {@Overrideprotected Void doInBackground(Void... arg0) {// TODO Auto-generated method stubmDownloadHttpTool.ready();return null;}@Overrideprotected void onPostExecute(Void result) {// TODO Auto-generated method stubsuper.onPostExecute(result);fileSize = mDownloadHttpTool.getFileSize();downloadedSize = mDownloadHttpTool.getCompeleteSize();Log.w("Tag", "downloadedSize::" + downloadedSize);if (onDownloadListener != null) {onDownloadListener.downloadStart(fileSize);}mDownloadHttpTool.start();}}.execute();}public void pause() {mDownloadHttpTool.pause();}public void delete(){mDownloadHttpTool.delete();}public void reset(){mDownloadHttpTool.delete();start();}public void setOnDownloadListener(OnDownloadListener onDownloadListener) {this.onDownloadListener = onDownloadListener;}//下载回调接口public interface OnDownloadListener {public void downloadStart(int fileSize);public void downloadProgress(int downloadedSize);//记录当前所有线程下总和public void downloadEnd();}
}

在MainActivity

package com.example.test;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import com.example.test.DownloadUtil.OnDownloadListener;
public class MainActivity extends FragmentActivity {private static final String TAG = MainActivity.class.getSimpleName();private ProgressBar mProgressBar;private Button start;private Button pause;private Button delete;private Button reset;private TextView total;private int max;private DownloadUtil mDownloadUtil;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mProgressBar = (ProgressBar) findViewById(R.id.progressBar1);start = (Button) findViewById(R.id.button_start);pause = (Button) findViewById(R.id.button_pause);delete = (Button) findViewById(R.id.button_delete);reset = (Button) findViewById(R.id.button_reset);total = (TextView) findViewById(R.id.textView_total);String urlString = "http://bbra.cn/Uploadfiles/imgs/20110303/fengjin/013.jpg";String localPath = Environment.getExternalStorageDirectory().getAbsolutePath() + "/local";mDownloadUtil = new DownloadUtil(2, localPath, "abc.jpg", urlString,this);mDownloadUtil.setOnDownloadListener(new OnDownloadListener() {@Overridepublic void downloadStart(int fileSize) {// TODO Auto-generated method stubLog.w(TAG, "fileSize::" + fileSize);max = fileSize;mProgressBar.setMax(fileSize);}@Overridepublic void downloadProgress(int downloadedSize) {// TODO Auto-generated method stubLog.w(TAG, "Compelete::" + downloadedSize);mProgressBar.setProgress(downloadedSize);total.setText((int) downloadedSize * 100 / max + "%");}@Overridepublic void downloadEnd() {// TODO Auto-generated method stubLog.w(TAG, "ENd");}});start.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubmDownloadUtil.start();}});pause.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubmDownloadUtil.pause();}});delete.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubmDownloadUtil.delete();}});reset.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {// TODO Auto-generated method stubmDownloadUtil.reset();}});}
}