Android实现网络多线程断点续传下载

本示例介绍在Android平台下通过HTTP协议实现断点续传下载。



我们编写的是Andorid的HTTP协议多线程断点下载应用程序。直接使用单线程下载HTTP文件对我们来说是一件非常简单的事。那么，多线程断点需要什么功能？

1.多线程下载，

2.支持断点。

使用多线程的好处：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();//获取下载文件的长度

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");

[b] (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。[/b]

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

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

程序结构如下图所示：



string.xml文件中代码：



<?xml version="1.0" encoding="utf-8"?>
<resources>

<string name="hello">Hello World, MainActivity!</string>

<string name="app_name">Android网络多线程断点下载</string>

<string name="path">下载路径</string>

<string name="downloadbutton">下载</string>

<string name="sdcarderror">SDCard不存在或者写保护</string>

<string name="success">下载完成</string>

<string name="error">下载失败</string>

</resources>




main.xml文件中代码：



<?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">

<!-- 下载路径 -->

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/path"/>

<EditText

android:id="@+id/path"

android:text="http://www.winrar.com.cn/download/wrar380sc.exe"

android:layout_width="fill_parent"

android:layout_height="wrap_content">

</EditText>

<!-- 下载按钮 -->

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/downloadbutton"

android:id="@+id/button"/>

<!-- 进度条 -->

<ProgressBar

android:layout_width="fill_parent"

android:layout_height="20dip"

style="?android:attr/progressBarStyleHorizontal"

android:id="@+id/downloadbar" />

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:gravity="center"

android:id="@+id/resultView" />

</LinearLayout>




AndroidManifest.xml文件中代码：



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

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

<application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".MainActivity"

android:label="@string/app_name">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

</application>

<!-- 在SDCard中创建与删除文件权限 -->

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

<!-- 往SDCard写入数据权限 -->

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

<!-- 访问internet权限 -->

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

</manifest>






MainActivity中代码：




package com.android.downloader;
import java.io.File;

import com.android.network.DownloadProgressListener;

import com.android.network.FileDownloader;

import android.app.Activity;

import android.os.Bundle;

import android.os.Environment;

import android.os.Handler;

import android.os.Message;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.ProgressBar;

import android.widget.TextView;

import android.widget.Toast;

public class MainActivity extends Activity {

private EditText downloadpathText;

private TextView resultView;

private ProgressBar progressBar;

/**

* 当Handler被创建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(){

@Override

public void handleMessage(Message msg) {

switch (msg.what) {

case 1:

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

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

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

resultView.setText(result+ "%");

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

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

}

break;

case -1:

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

break;

}

}

};

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

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

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

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

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

button.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

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

System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED);

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

download(path, Environment.getExternalStorageDirectory());

}else{

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

}

}

});

}

/**

* 主线程(UI线程)

* 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

* @param path

* @param savedir

*/

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

new Thread(new Runnable() {

@Override

public void run() {

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

progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度为文件的长度

try {

loader.download(new DownloadProgressListener() {

@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();

msg.what = 1;

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

handler.sendMessage(msg);//发送消息

}

});

} catch (Exception e) {

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

}

}

}).start();

}
}




DBOpenHelper中代码：




package com.android.service;
import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

public class DBOpenHelper extends SQLiteOpenHelper {

private static final String DBNAME = "down.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);

}

}



FileService中代码：




package com.android.service;
import java.util.HashMap;

import java.util.Map;

import android.content.Context;

import android.database.Cursor;

import android.database.sqlite.SQLiteDatabase;

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<Integer, Integer> getData(String path){

SQLiteDatabase db = openHelper.getReadableDatabase();

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

Map<Integer, Integer> data = new HashMap<Integer, Integer>();

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<Integer, Integer> map){//int threadid, int position

SQLiteDatabase db = openHelper.getWritableDatabase();

db.beginTransaction();

try{

for(Map.Entry<Integer, Integer> 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<Integer, Integer> map){

SQLiteDatabase db = openHelper.getWritableDatabase();

db.beginTransaction();

try{

for(Map.Entry<Integer, Integer> 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();

}
}




DownloadProgressListener中代码：

package com.android.network;
public interface DownloadProgressListener {

public void onDownloadSize(int size);
}

FileDownloader中代码：




package com.android.network;
import java.io.File;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import java.util.LinkedHashMap;

import java.util.Map;

import java.util.UUID;

import java.util.concurrent.ConcurrentHashMap;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

import com.android.service.FileService;

import android.content.Context;

import android.util.Log;

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<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();

/* 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);

}

/**

* 构建文件下载器

* @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) {

this.fileSize = conn.getContentLength();//根据响应获取文件大小

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

String filename = getFileName(conn);//获取文件名称

this.saveFile = new File(fileSaveDir, filename);//构建保存文件

Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//获取下载记录

if(logdata.size()>0){//如果存在下载记录

for(Map.Entry<Integer, Integer> entry : logdata.entrySet())

data.put(entry.getKey(), entry.getValue());//把各条线程已经下载的数据长度放入data中

}

if(this.data.size()==this.threads.length){//下面计算所有线程已经下载的数据长度

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

this.downloadSize += this.data.get(i+1);

}

print("已经下载的长度"+ this.downloadSize);

}

//计算每条线程下载的数据长度

this.block = (this.fileSize % this.threads.length)==0? this.fileSize / this.threads.length : this.fileSize /this.threads.length + 1;

}else{

throw new RuntimeException("server no response ");

}

} catch (Exception e) {

print(e.toString());

throw new RuntimeException("don't connection this url");

}

}

/**

* 获取文件名

* @param conn

* @return

*/

private String getFileName(HttpURLConnection conn) {

String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);

if(filename==null || "".equals(filename.trim())){//如果获取不到文件名称

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

String mine = conn.getHeaderField(i);

if (mine == null) break;

if("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())){

Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());

if(m.find()) return m.group(1);

}

}

filename = UUID.randomUUID()+ ".tmp";//默认取一个文件名

}

return filename;

}

/**

* 开始下载文件

* @param listener 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null

* @return 已下载文件大小

* @throws Exception

*/

public int download(DownloadProgressListener listener) throws Exception{

try {

RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");

if(this.fileSize>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++) {

this.data.put(i+1, 0);//初始化每条线程已经下载的数据长度为0

}

}

for (int i = 0; i < this.threads.length; i++) {//开启线程进行下载

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

if(downLength < this.block && this.downloadSize<this.fileSize){//判断线程是否已经完成下载,否则继续下载

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();

}else{

this.threads[i] = null;

}

}

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

boolean notFinish = true;//下载未完成

while (notFinish) {// 循环判断所有线程是否完成下载

Thread.sleep(900);

notFinish = false;//假定全部线程下载完成

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

if (this.threads[i] != null && !this.threads[i].isFinish()) {//如果发现线程未完成下载

notFinish = true;//设置标志为下载没有完成

if(this.threads[i].getDownLength() == -1){//如果下载失败,再重新下载

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();

}

}

}

if(listener!=null) listener.onDownloadSize(this.downloadSize);//通知目前已经下载完成的数据长度

}

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<String, String> getHttpResponseHeader(HttpURLConnection http) {

Map<String, String> header = new LinkedHashMap<String, String>();

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<String, String> header = getHttpResponseHeader(http);

for(Map.Entry<String, String> entry : header.entrySet()){

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

print(key+ entry.getValue());

}

}

private static void print(String msg){

Log.i(TAG, msg);

}

}



DownloadThread 中代码：




package com.android.network;
import java.io.File;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import android.util.Log;

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;

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() {

if(downLength < block){//未下载完成

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");

int startPos = block * (threadId - 1) + downLength;//开始位置

int endPos = block * threadId -1;//结束位置

http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围

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");

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;

}
}




运行效果如下：