Android 下使用 Http 协议实现多线程断点续传下载

0.使用多线程下载会提升文件下载的速度，那么多线程下载文件的过程是：

(1)首先获得下载文件的长度，然后设置本地文件的长度

HttpURLConnection.getContentLength();

RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");

file.setLength(filesize);//设置本地文件的长度

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示。



例如10M大小，使用3个线程来下载，

线程下载的数据长度 (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M

下载开始位置：线程id*每条线程下载的数据长度 = ?

下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

(3)使用Http的Range头字段指定每条线程从文件的什么位置开始下载，下载到什么位置为止，

如：指定从文件的2M位置开始下载，下载到位置(4M-1byte)为止

代码如下：HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");

(4)保存文件，使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。

RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");

threadfile.seek(2097152);//从文件的什么位置开始写入数据

1.多线程下载的核心代码示例

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public class MulThreadDownload

{

/**

* 多线程下载

* @param args

*/

public static void main(String[] args)

{

String path = "http://net.hoo.com/QQWubiSetup.exe";

try

{

new MulThreadDownload().download(path, 3);

}

catch (Exception e)

{

e.printStackTrace();

}

}

/**

* 从路径中获取文件名称

* @param path 下载路径

* @return

*/

public static String getFilename(String path)

{

return path.substring(path.lastIndexOf('/')+1);

}

/**

* 下载文件

* @param path 下载路径

* @param threadsize 线程数

*/

public void download(String path, int threadsize) throws Exception

{

URL url = new URL(path);

HttpURLConnection conn = (HttpURLConnection)url.openConnection();

conn.setRequestMethod("GET");

conn.setConnectTimeout(5 * 1000);

//获取要下载的文件的长度

int filelength = conn.getContentLength();

//从路径中获取文件名称

String filename = getFilename(path);

File saveFile = new File(filename);

RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");

//设置本地文件的长度和下载文件相同

accessFile.setLength(filelength);

accessFile.close();

//计算每条线程下载的数据长度

int block = filelength%threadsize==0? filelength/threadsize : filelength/threadsize+1;

for(int threadid=0 ; threadid < threadsize ; threadid++){

new DownloadThread(url, saveFile, block, threadid).start();

}

}

private final class DownloadThread extends Thread

{

private URL url;

private File saveFile;

private int block;//每条线程下载的数据长度

private int threadid;//线程id

public DownloadThread(URL url, File saveFile, int block, int threadid)

{

this.url = url;

this.saveFile = saveFile;

this.block = block;

this.threadid = threadid;

}

@Override

public void run()

{

//计算开始位置公式：线程id*每条线程下载的数据长度= ？

//计算结束位置公式：（线程id +1）*每条线程下载的数据长度-1 =?

int startposition = threadid * block;

int endposition = (threadid + 1 ) * block - 1;

try

{

RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");

//设置从什么位置开始写入数据

accessFile.seek(startposition);

HttpURLConnection conn = (HttpURLConnection)url.openConnection();

conn.setRequestMethod("GET");

conn.setConnectTimeout(5 * 1000);

conn.setRequestProperty("Range", "bytes="+ startposition+ "-"+ endposition);

InputStream inStream = conn.getInputStream();

byte[] buffer = new byte[1024];

int len = 0;

while( (len=inStream.read(buffer)) != -1 )

{

accessFile.write(buffer, 0, len);

}

inStream.close();

accessFile.close();

System.out.println("线程id:"+ threadid+ "下载完成");

}

catch (Exception e)

{

e.printStackTrace();

}

}

}

}

2.多线程断点下载功能，这里把断点数据保存到数据库中：注意代码注释的理解

(0)主Activity，关键点使用Handler更新进度条与开启线程下载避免ANR

若不使用Handler却要立即更新进度条数据，可使用：

//resultView.invalidate(); UI线程中立即更新进度条方法

//resultView.postInvalidate(); 非UI线程中立即更新进度条方法

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/**

* 注意这里的设计思路，UI线程与参数保存问题，避免ANR问题，UI控件的显示

* @author kay

*

*/

public class DownloadActivity extends Activity

{

private EditText downloadpathText;

private TextView resultView;

private ProgressBar progressBar;

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

downloadpathText = (EditText) this.findViewById(R.id.downloadpath);

progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);

resultView = (TextView) this.findViewById(R.id.result);

Button button = (Button) this.findViewById(R.id.button);

button.setOnClickListener(new View.OnClickListener()

{

@Override

public void onClick(View v)

{

//取得下载路径

String path = downloadpathText.getText().toString();

//判断SDCard是否存在

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))

{

//下载操作

download(path, Environment.getExternalStorageDirectory());

}

else

{

Toast.makeText(DownloadActivity.this, R.string.sdcarderror, 1).show();

}

}

});

}

//主线程(UI线程)

//业务逻辑正确，但是该程序运行的时候有问题(可能出现ANR问题)

//对于显示控件的界面更新只是由UI线程负责，如果是在非UI线程更新控件的属性值，更新后的显示界面不会反映到屏幕上

/**

* 参数类型：因为启动一个线程还需要使用到上面方法的参数，而主方法启动后很快就会销毁，

* 那么使用Final可以解决参数丢失的问题

* path 注意是Final类型

* savedir 注意是Final类型

*/

private void download(final String path, final File savedir)

{

//这里开启一个线程避免ANR错误

new Thread(new Runnable()

{

@Override

public void run()

{

FileDownloader loader = new FileDownloader(DownloadActivity.this, path, savedir, 3);

//设置进度条的最大刻度为文件的长度

progressBar.setMax(loader.getFileSize());

try

{

loader.download(new DownloadProgressListener()

{

/**

* 注意这里的设计，显示进度条数据需要使用Handler来处理

* 因为非UI线程更新后的数据不能被刷新

*/

@Override

public void onDownloadSize(int size)

{

//实时获知文件已经下载的数据长度

Message msg = new Message();

//设置消息标签

msg.what = 1;

msg.getData().putInt("size", size);

//使用Handler对象发送消息

handler.sendMessage(msg);

}

});

}

catch (Exception e)

{

//发送一个空消息到消息队列

handler.obtainMessage(-1).sendToTarget();

/**

* 或者使用下面的方法发送一个空消息

* Message msg = new Message();

* msg.what = 1;

* handler.sendMessage(msg);

*/

}

}

}).start();

}

/**Handler原理：当Handler被创建时会关联到创建它的当前线程的消息队列，该类用于往消息队列发送消息

*

* 消息队列中的消息由当前线程内部进行处理

*/

private Handler handler = new Handler()

{

//重写Handler里面的handleMessage方法处理消息

@Override

public void handleMessage(Message msg)

{

switch (msg.what)

{

case 1:

//进度条显示

progressBar.setProgress(msg.getData().getInt("size"));

float num = (float)progressBar.getProgress()/(float)progressBar.getMax();

int result = (int)(num*100);

//resultView.invalidate(); UI线程中立即更新进度条方法

//resultView.postInvalidate(); 非UI线程中立即更新进度条方法

resultView.setText(result+ "%");

//判断是否下载成功

if(progressBar.getProgress()==progressBar.getMax())

{

Toast.makeText(DownloadActivity.this, R.string.success, 1).show();

}

break;

case -1:

Toast.makeText(DownloadActivity.this, R.string.error, 1).show();

break;

}

}

};

}

(1)下载类：

注意计算每条线程的下载长度与下载起始位置的方法

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public class DownloadThread extends Thread

{

private static final String TAG = "DownloadThread";

private File saveFile;

private URL downUrl;

private int block;

//下载开始位置

private int threadId = -1;

//下载文件长度

private int downLength;

private boolean finish = false;

private FileDownloader downloader;

public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId)

{

this.downUrl = downUrl;

this.saveFile = saveFile;

this.block = block;

this.downloader = downloader;

this.threadId = threadId;

this.downLength = downLength;

}

@Override

public void run()

{

//未下载完成

if(downLength < block)

{

try

{

HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();

http.setConnectTimeout(5 * 1000);

http.setRequestMethod("GET");

http.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml,
application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");

http.setRequestProperty("Accept-Language", "zh-CN");

http.setRequestProperty("Referer", downUrl.toString());

http.setRequestProperty("Charset", "UTF-8");

//下载开始位置：线程id*每条线程下载的数据长度 = ?

int startPos = block * (threadId - 1) + downLength;

//下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

int endPos = block * threadId -1;

//设置获取实体数据的范围

http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);

http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET
CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");

http.setRequestProperty("Connection", "Keep-Alive");

InputStream inStream = http.getInputStream();

byte[] buffer = new byte[1024];

int offset = 0;

print("Thread " + this.threadId + " start download from position "+ startPos);

RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");

threadfile.seek(startPos);

while ((offset = inStream.read(buffer, 0, 1024)) != -1)

{

threadfile.write(buffer, 0, offset);

downLength += offset;

downloader.update(this.threadId, downLength);

downloader.append(offset);

}

threadfile.close();

inStream.close();

print("Thread " + this.threadId + " download finish");

//标记是否完成

this.finish = true;

}

catch (Exception e)

{

this.downLength = -1;

print("Thread "+ this.threadId+ ":"+ e);

}

}

}

private static void print(String msg)

{

Log.i(TAG, msg);

}

/**

* 下载是否完成

* @return

*/

public boolean isFinish()

{

return finish;

}

/**

* 已经下载的内容大小

* @return 如果返回值为-1,代表下载失败

*/

public long getDownLength()

{

return downLength;

}

}

文件下载器，使用

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/**

* 文件下载器,使用这个类的方法如下示例：

* FileDownloader loader = new FileDownloader(context, "http://browse.babasport.com/ejb3/ActivePort.exe",

* new File("D:\\androidsoft\\test"), 2);

* loader.getFileSize();//得到文件总大小

* try {

* loader.download(new DownloadProgressListener(){

* public void onDownloadSize(int size) {

* print("已经下载："+ size);

* }

* });

* }

* catch (Exception e)

* {

* e.printStackTrace();

* }

*/

public class FileDownloader

{

private static final String TAG = "FileDownloader";

private Context context;

private FileService fileService;

//已下载文件长度

private int downloadSize = 0;

//原始文件长度

private int fileSize = 0;

///线程数

private DownloadThread[] threads;

//本地保存文件

private File saveFile;

//缓存各线程下载的长度

private Map data = new ConcurrentHashMap();

//每条线程下载的长度

private int block;

//下载路径

private String downloadUrl;

//获取线程数

public int getThreadSize()

{

return threads.length;

}

/**

* 获取文件大小

* @return

*/

public int getFileSize()

{

return fileSize;

}

/**

* 累计已下载大小

* @param size

*/

protected synchronized void append(int size)

{

downloadSize += size;

}

/**

* 更新指定线程最后下载的位置

* @param threadId 线程id

* @param pos 最后下载的位置

*/

protected synchronized void update(int threadId, int pos)

{

this.data.put(threadId, pos);

this.fileService.update(this.downloadUrl, this.data);

}

/**

* 文件下载构造器

* @param downloadUrl 下载路径

* @param fileSaveDir 文件保存目录

* @param threadNum 下载线程数

*/

public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum)

{

try

{

this.context = context;

this.downloadUrl = downloadUrl;

fileService = new FileService(this.context);

URL url = new URL(this.downloadUrl);

if(!fileSaveDir.exists()) fileSaveDir.mkdirs();

this.threads = new DownloadThread[threadNum];

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5*1000);

conn.setRequestMethod("GET");

conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml,
application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");

conn.setRequestProperty("Accept-Language", "zh-CN");

conn.setRequestProperty("Referer", downloadUrl);

conn.setRequestProperty("Charset", "UTF-8");

conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET
CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");

conn.setRequestProperty("Connection", "Keep-Alive");

conn.connect();

printResponseHeader(conn);

if (conn.getResponseCode()==200)

{

//根据响应获取文件大小

this.fileSize = conn.getContentLength();

if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");

//获取文件名称

String filename = getFileName(conn);

//构建保存文件

this.saveFile = new File(fileSaveDir, filename);

//获取下载记录

Map logdata = fileService.getData(downloadUrl);

//如果存在下载记录

if(logdata.size()>0)

{

//把各条线程已经下载的数据长度放入data中

for(Map.Entry entry : logdata.entrySet())

data.put(entry.getKey(), entry.getValue());

}

//下面计算所有线程已经下载的数据长度

if(this.data.size()==this.threads.length)

{

for (int i = 0; i 0) randOut.setLength(this.fileSize);

randOut.close();

URL url = new URL(this.downloadUrl);

if(this.data.size() != this.threads.length)

{

this.data.clear();

for (int i = 0; i < this.threads.length; i++)

{

//初始化每条线程已经下载的数据长度为0

this.data.put(i+1, 0);

}

}

//开启线程进行下载

for (int i = 0; i < this.threads.length; i++)

{

int downLength = this.data.get(i+1);

//判断线程是否已经完成下载,否则继续下载

if(downLength < this.block && this.downloadSize<this.fileSize)

{

this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);

this.threads[i].setPriority(7);//可删除这条

this.threads[i].start();

}

else

{

this.threads[i] = null;

}

}

this.fileService.save(this.downloadUrl, this.data);

//下载未完成

boolean notFinish = true;

// 循环判断所有线程是否完成下载

while (notFinish)

{

Thread.sleep(900);

//假定全部线程下载完成

notFinish = false;

for (int i = 0; i < this.threads.length; i++)

{

//如果发现线程未完成下载

if (this.threads[i] != null && !this.threads[i].isFinish())

{

//设置标志为下载没有完成

notFinish = true;

//如果下载失败,再重新下载

if(this.threads[i].getDownLength() == -1)

{

this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);

this.threads[i].setPriority(7);

this.threads[i].start();

}

}

}

//通知目前已经下载完成的数据长度

if(listener!=null) listener.onDownloadSize(this.downloadSize);

}

//删除数据库中下载信息

fileService.delete(this.downloadUrl);

}

catch (Exception e)

{

print(e.toString());

throw new Exception("file download fail");

}

return this.downloadSize;

}

/**

* 获取Http响应头字段

* @param http

* @return

*/

public static Map getHttpResponseHeader(HttpURLConnection http) {

Map header = new LinkedHashMap();

for (int i = 0;; i++) {

String mine = http.getHeaderField(i);

if (mine == null) break;

header.put(http.getHeaderFieldKey(i), mine);

}

return header;

}

/**

* 打印Http头字段

* @param http

*/

public static void printResponseHeader(HttpURLConnection http)

{

Map header = getHttpResponseHeader(http);

for(Map.Entry entry : header.entrySet())

{

String key = entry.getKey()!=null ? entry.getKey()+ ":" : "";

print(key+ entry.getValue());

}

}

private static void print(String msg)

{

Log.i(TAG, msg);

}

}

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public interface DownloadProgressListener

{

public void onDownloadSize(int size);

}

(2)文件操作，断点数据库存储

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public class DBOpenHelper extends SQLiteOpenHelper

{

private static final String DBNAME = "itcast.db";

private static final int VERSION = 1;

public DBOpenHelper(Context context)

{

super(context, DBNAME, null, VERSION);

}

@Override

public void onCreate(SQLiteDatabase db)

{

db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER,
downlength INTEGER)");

}

@Override

public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)

{

db.execSQL("DROP TABLE IF EXISTS filedownlog");

onCreate(db);

}

}

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/**

* 文件下载业务bean

*/

public class FileService

{

private DBOpenHelper openHelper;

public FileService(Context context)

{

openHelper = new DBOpenHelper(context);

}

/**

* 获取每条线程已经下载的文件长度

* @param path

* @return

*/

public Map getData(String path)

{

SQLiteDatabase db = openHelper.getReadableDatabase();

Cursor cursor = db.rawQuery("select threadid, downlength from filedownlog where downpath=?", new String[]{path});

Map data = new HashMap();

while(cursor.moveToNext())

{

data.put(cursor.getInt(0), cursor.getInt(1));

}

cursor.close();

db.close();

return data;

}

/**

* 保存每条线程已经下载的文件长度

* @param path

* @param map

*/

public void save(String path, Map map)

{//int threadid, int position

SQLiteDatabase db = openHelper.getWritableDatabase();

db.beginTransaction();

try

{

for(Map.Entry entry : map.entrySet())

{

db.execSQL("insert into filedownlog(downpath, threadid, downlength) values(?,?,?)",

new Object[]{path, entry.getKey(), entry.getValue()});

}

db.setTransactionSuccessful();

}

finally

{

db.endTransaction();

}

db.close();

}

/**

* 实时更新每条线程已经下载的文件长度

* @param path

* @param map

*/

public void update(String path, Map map)

{

SQLiteDatabase db = openHelper.getWritableDatabase();

db.beginTransaction();

try{

for(Map.Entry entry : map.entrySet()){

db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",

new Object[]{entry.getValue(), path, entry.getKey()});

}

db.setTransactionSuccessful();

}finally{

db.endTransaction();

}

db.close();

}

/**

* 当文件下载完成后，删除对应的下载记录

* @param path

*/

public void delete(String path)

{

SQLiteDatabase db = openHelper.getWritableDatabase();

db.execSQL("delete from filedownlog where downpath=?", new Object[]{path});

db.close();

}

}