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id
private 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;
}
@Override
public 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
*/
@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) {
}
}
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;
}
@Override
public 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() {
@Override
public void handleMessage(Message msg) {
// TODO Auto-generated method stub
super.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>() {
@Override
protected Void doInBackground(Void... arg0) {
// TODO Auto-generated method stub
mDownloadHttpTool.ready();
return null;
}
@Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
super.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;
@Override
protected 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() {
@Override
public void downloadStart(int fileSize) {
// TODO Auto-generated method stub
Log.w(TAG, "fileSize::" + fileSize);
max = fileSize;
mProgressBar.setMax(fileSize);
}
@Override
public void downloadProgress(int downloadedSize) {
// TODO Auto-generated method stub
Log.w(TAG, "Compelete::" + downloadedSize);
mProgressBar.setProgress(downloadedSize);
total.setText((int) downloadedSize * 100 / max + "%");
}
@Override
public void downloadEnd() {
// TODO Auto-generated method stub
Log.w(TAG, "ENd");
}
});
start.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mDownloadUtil.start();
}
});
pause.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mDownloadUtil.pause();
}
});
delete.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mDownloadUtil.delete();
}
});
reset.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
mDownloadUtil.reset();
}
});
}
}