1.上篇实现了单线程的单文件下载，本篇将讲述多个文件的多线程下载，
在此之前希望你先弄懂上篇
最终静态的效果
最终动态的效果
一、分析一下多线程下载单个文件的原理：
1.线程分工方式
大家都知道，一个文件是很多的字节组成的，字节又是由二进制的位组成，如果把一个字节当成一块砖。
那下载就像把服务器的砖头搬到手机里，然后摆在一个文件里摆好，搬完了，文件满了，任务就完成了
然后文件是电影就能播，是图片就能看，app就能安装。
对于下载一个文件，上篇讲的单线程下载相当于一个人一块一块地搬。
而本篇的多线程则是雇几个人来搬，可想而知效率是更高的。
那我开一千个线程岂不是秒下?如 果你要搬1000 块砖，找1000 个人，效率固然高，
但人家也不是白干活，相对于3 个人搬，你要多付333 倍的工资，也就是开线程要消耗的，适量即可。
一个字节的丢失就可能导致一个文件的损坏，可想而知要多个人一起干活必须分工明确
2.多线程下载的流程图
整体架构和单线程的下载类似，最大的改变的是：
由于多线程需要管理，使用一个DownLoadTask来管理一个文件的所有下载线程，其中封装了下载和暂停逻辑。
在DownLoadTask#download方法里，如果数据库没有信息，则进行线程的任务分配及线程信息的创建，并插入数据库。
DownLoadThread作为DownLoadTask的内部类，方便使用。最后在download方法一一创建DownLoadThread并开启，
将DownLoadThread存入集合管理,在DownLoadTask#pause方法里，将集合中的线程全部关闭即可
二、代码实现：
1.RecyclerView的使用：
用RecyclerView将单个条目便成一个列表界面
1).增加URL常量
public static final String URL_JUEJIN = "https://imtt.dd.qq.com/16891/4611E43165D203CB6A52E65759FE7641.apk?fsname=com.daimajia.gold_5.6.2_196.apk&csr=1bbd" ;
public static final String URL_QQ = "https://qd.myapp.com/myapp/qqteam/Androidlite/qqlite_3.7.1.704_android_r110206_GuanWang_537057973_release_10000484.apk" ;
public static final String URL_YOUDAO = "http://codown.youdao.com/note/youdaonote_android_6.3.5_youdaoweb.apk" ;
public static final String URL_WEIXIN = "http://gdown.baidu.com/data/wisegame/3d4de3ae1d2dc7d5/weixin_1360.apk" ;
public static final String URL_YOUDAO_CIDIAN = "http://codown.youdao.com/dictmobile/youdaodict_android_youdaoweb.apk" ;
2).初始化数据
* 初始化数据
* @return
@NonNull
private ArrayList<FileBean> initData() {
FileBean juejin = new FileBean(0 , Cons.URL_JUEJIN, "掘金.apk" , 0 , 0 )
FileBean yunbiji = new FileBean(1 , Cons.URL_YOUDAO, "有道云笔记.apk" , 0 , 0 )
FileBean qq = new FileBean(2 , Cons.URL_QQ, "QQ.apk" , 0 , 0 )
FileBean weiChat = new FileBean(3 , Cons.URL_WEIXIN, "微信.apk" , 0 , 0 )
FileBean cidian = new FileBean(4 , Cons.URL_YOUDAO_CIDIAN, "有道词典.apk" , 0 , 0 )
ArrayList<FileBean> fileBeans = new ArrayList<>()
fileBeans.add(juejin)
fileBeans.add(yunbiji)
fileBeans.add(qq)
fileBeans.add(weiChat)
fileBeans.add(cidian)
return fileBeans
3).RecyclerView适配器
上篇在Activity中的按钮中实现的下载和暂停intent，这里放在RVAdapter里
* 作者：张风捷特烈<br/>
* 时间：2018/11/13 0013:11:58<br/>
* 邮箱：1981462002@qq.com<br/>
* 说明：RecyclerView适配器
public class RVAdapter extends RecyclerView.Adapter<MyViewHolder> {
private Context mContext
private List<FileBean> mData
public RVAdapter(Context context, List<FileBean> data) {
mContext = context
mData = data
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(mContext).inflate(R.layout.item_pb, parent, false )
view.setOnClickListener(v -> {
//TODO 点击条目
return new MyViewHolder(view)
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
FileBean fileBean = mData.get(position)
holder.mBtnStart.setOnAlphaListener(v -> {
ToastUtil.showAtOnce(mContext, "开始下载: " + fileBean.getFileName())
Intent intent = new Intent(mContext, DownLoadService.class)
intent.setAction(Cons.ACTION_START)
intent.putExtra(Cons.SEND_FILE_BEAN, fileBean)
mContext.startService(intent)
holder.mBtnStop.setOnAlphaListener(v -> {
Intent intent = new Intent(mContext, DownLoadService.class)
intent.setAction(Cons.ACTION_STOP)
intent.putExtra(Cons.SEND_FILE_BEAN, fileBean)
mContext.startService(intent)
ToastUtil.showAtOnce(mContext, "停止下载: " + fileBean.getFileName())
holder.mTVFileName.setText(fileBean.getFileName())
holder.mPBH.setProgress((int) fileBean.getLoadedLen())
holder.mPBV.setProgress((int) fileBean.getLoadedLen())
@Override
public int getItemCount() {
return mData.size()
* 更新进度
* @param id 待更新的文件id
* @param progress 进度数
public void updateProgress(int id, int progress) {
mData.get(id).setLoadedLen(progress)
notifyDataSetChanged()
* ViewHolder
class MyViewHolder extends RecyclerView.ViewHolder {
public ProgressBar mPBH
public ProgressBar mPBV
public AlphaImageView mBtnStart
public AlphaImageView mBtnStop
public TextView mTVFileName
public MyViewHolder(View itemView) {
super(itemView)
mPBH = itemView.findViewById(R.id.id_pb_h)
mPBV = itemView.findViewById(R.id.id_pb_v)
mBtnStart = itemView.findViewById(R.id.id_btn_start)
mBtnStop = itemView.findViewById(R.id.id_btn_stop)
mTVFileName = itemView.findViewById(R.id.id_tv_file_name)
4).设置适配器：MainActivity中
mAdapter = new RVAdapter (this , fileBeans);
mIdRvPage.setAdapter (mAdapter);
mIdRvPage.setLayoutManager (new LinearLayoutManager (this , LinearLayoutManager.VERTICAL, false ));
2.DownLoadTask的分析：
DownLoadTask最重要的在于：管理一个文件下载的所有线程，download是暴漏出的下载方法。pause停止。
三个线程共同工作
暂停时数据库情况
* 作者：张风捷特烈<br/>
* 时间：2018/11/13 0013:15:21<br/>
* 邮箱：1981462002@qq.com<br/>
* 说明：下载一个文件的任务(mDownLoadThreads储存该文件任务的所有线程)
public class DownLoadTask {
private FileBean mFileBean;
private DownLoadDao mDao;
private Context mContext;
private int mThreadCount;
public boolean isDownLoading;
private Timer mTimer;
private List<DownLoadThread> mDownLoadThreads;
private volatile AtomicLong mLoadedLen = new AtomicLong ();
public static ExecutorService sExe = Executors.newCachedThreadPool ();
public DownLoadTask (FileBean fileBean, Context context, int threadCount) {
mFileBean = fileBean;
mContext = context;
mThreadCount = threadCount;
mDao = new DownLoadDaoImpl (context);
mDownLoadThreads = new ArrayList<>();
mTimer = new Timer ();
* 下载逻辑
public void download () {
List<ThreadBean> threads = mDao.getThreads (mFileBean.getUrl());
if (threads.size() == 0 ) {
long len = mFileBean.getLength () / mThreadCount;
for (int i = 0 ; i < mThreadCount; i++) {
ThreadBean threadBean = null;
if (i != mThreadCount - 1 ) {
threadBean = new ThreadBean (
i, mFileBean.getUrl(), len * i , (i + 1 ) * len - 1 , 0 );
} else {
threadBean = new ThreadBean (
i, mFileBean.getUrl(), len * i , mFileBean.getLength (), 0 );
threads.add (threadBean);
mDao.insertThread (threadBean);
for (ThreadBean info : threads) {
DownLoadThread thread = new DownLoadThread (info);
sExe.execute (thread);
thread.isDownLoading = true;
isDownLoading = true;
mDownLoadThreads.add (thread);
mTimer.schedule (new TimerTask() {
@Override
public void run() {
Intent intent = new Intent (Cons.ACTION_UPDATE);
mContext.sendBroadcast (intent);
intent.putExtra (Cons.SEND_LOADED_PROGRESS,
(int) (mLoadedLen.get() * 100 / mFileBean.getLength ()));
intent.putExtra (Cons.SEND_FILE_ID, mFileBean.getId());
mContext.sendBroadcast (intent);
}, 1000 , 1000 );
public void pause () {
for (DownLoadThread downLoadThread : mDownLoadThreads) {
downLoadThread.isDownLoading = false;
isDownLoading = false;
* 下载的核心线程类
public class DownLoadThread extends Thread {
private ThreadBean mThreadBean;
public boolean isDownLoading;
public DownLoadThread (ThreadBean threadBean) {
mThreadBean = threadBean;
@Override
public void run() {
if (mThreadBean == null) {
return;
HttpURLConnection conn = null;
RandomAccessFile raf = null;
InputStream is = null;
try {
URL url = new URL (mThreadBean.getUrl());
conn = (HttpURLConnection) url.openConnection ();
conn.setConnectTimeout (5000 );
conn.setRequestMethod ("GET");
long start = mThreadBean.getStart () + mThreadBean.getLoadedLen ();
conn.setRequestProperty ("Range", "bytes=" + start + "-" + mThreadBean.getEnd());
File file = new File (Cons.DOWNLOAD_DIR, mFileBean.getFileName());
raf = new RandomAccessFile (file, "rwd");
raf.seek (start);
mLoadedLen.set (mLoadedLen.get() + mThreadBean.getLoadedLen ());
if (conn.getResponseCode() == 206 ) {
is = conn.getInputStream ();
byte[] buf = new byte[1024 * 4] ;
int len = 0 ;
while ((len = is.read(buf)) != -1 ) {
raf.write (buf, 0 , len);
mLoadedLen.set (mLoadedLen.get() + len);
mThreadBean.setLoadedLen (mThreadBean.getLoadedLen() + len);
if (!this.isDownLoading) {
mDao.updateThread (mThreadBean.getUrl(), mThreadBean.getId (),
mThreadBean.getLoadedLen ());
return;
isDownLoading = false;
checkIsAllOK ();
} catch (Exception e) {
e.printStackTrace ();
} finally {
if (conn != null) {
conn.disconnect ();
try {
if (raf != null) {
raf.close ();
if (is != null) {
is.close ();
} catch (IOException e) {
e.printStackTrace ();
* 检查是否所有线程都已经完成了
private synchronized void checkIsAllOK () {
boolean allFinished = true;
for (DownLoadThread downLoadThread : mDownLoadThreads) {
if (downLoadThread.isDownLoading) {
allFinished = false;
break;
if (allFinished) {
mTimer.cancel ();
mDao.deleteThread (mThreadBean.getUrl());
Intent intent = new Intent ();
intent.setAction (Cons.ACTION_FINISH);
intent.putExtra (Cons.SEND_FILE_BEAN, mFileBean);
mContext.sendBroadcast (intent);
3.Service 的修改
稍微不同的就是一个下载任务变成了多个下载任务，这里使用安卓特有的SparseArray来存储
* 作者：张风捷特烈<br/>
* 时间：2018/11/12 0012:12:23<br/>
* 邮箱：1981462002@qq.com<br/>
* 说明：下载的服务
public class DownLoadService extends Service {
private SparseArray<DownLoadTask> mTaskMap = new SparseArray <>();
* 处理消息使用的Handler
private Handler mHandler = new Handler () {
@Override
public void handleMessage (Message msg) {
switch (msg.what) {
case Cons.MSG_CREATE_FILE_OK:
FileBean fileBean = (FileBean) msg.obj;
ToastUtil.showAtOnce(DownLoadService.this , "文件长度:" + fileBean.getLength());
DownLoadTask task = new DownLoadTask (fileBean, DownLoadService.this , 3 );
task.download();
mTaskMap.put(fileBean.getId(), task);
break ;
@Override
public int onStartCommand (Intent intent, int flags, int startId) {
if (intent.getAction() != null ) {
switch (intent.getAction()) {
case Cons.ACTION_START:
FileBean fileBean = (FileBean) intent.getSerializableExtra(Cons.SEND_FILE_BEAN);
DownLoadTask start = mTaskMap.get(fileBean.getId());
if (start != null ) {
if (start.isDownLoading) {
return super .onStartCommand(intent, flags, startId);
DownLoadTask.sExe.execute(new LinkURLThread (fileBean, mHandler));
break ;
case Cons.ACTION_STOP:
FileBean stopFile = (FileBean) intent.getSerializableExtra(Cons.SEND_FILE_BEAN);
DownLoadTask task = mTaskMap.get(stopFile.getId());
if (task != null ) {
task.pause();
break ;
return super .onStartCommand(intent, flags, startId);
@Nullable
@Override
public IBinder onBind (Intent intent) {
return null ;
4.广播的处理：
这里多了一个下载完成的Action，并且由MainActivity传入进度条，改为mAdapter.updateProgress刷新视图
* 作者：张风捷特烈<br/>
* 时间：2018/11/12 0012:16:05<br/>
* 邮箱：1981462002@qq.com<br/>
* 说明：更新ui的广播接收者
public class UpdateReceiver extends BroadcastReceiver private RVAdapter mAdapter;
public UpdateReceiver (RVAdapter adapter) {
mAdapter = adapter;
@Override
public void onReceive(Context context, Intent intent) {
if (Cons .ACTION_UPDATE .equals(intent.getAction())) {
int loadedProgress = intent.getIntExtra(Cons .SEND_LOADED_PROGRESS , 0 );
int id = intent.getIntExtra(Cons .SEND_FILE_ID , 0 );
mAdapter.updateProgress(id, loadedProgress);
} else if (Cons .ACTION_FINISH .equals(intent.getAction())) {
FileBean fileBean = (FileBean ) intent.getSerializableExtra(Cons .SEND_FILE_BEAN );
mAdapter.updateProgress(fileBean.getId(), 0 );
ToastUtil .showAtOnce(context, "文佳下载完成：" + fileBean.getFileName());
三、数据库的多线程操作注意点：
1.DownLoadDBHelper的单例
为了避免不同线程拿到的DownLoadDBHelper对象不同，这里使用单例模式
private static DownLoadDBHelper sDownLoadDBHelper;
public static DownLoadDBHelper newInstance (Context context )if (sDownLoadDBHelper == null ) {
synchronized (DownLoadDBHelper.class ) {
if (sDownLoadDBHelper == null ) {
sDownLoadDBHelper = new DownLoadDBHelper(context);
return sDownLoadDBHelper;
2.在变动数据库的方法上加同步：db.DownLoadDaoImpl
避免多个线程修改数据库产生冲突
public synchronized void insertThread (ThreadBean threadBean)
public synchronized void deleteThread (String url)
public synchronized void updateThread (String url, int threadId, long loadedLen)
你看完上下两篇，基本上就能够实现这样的效果了：
回过头来看一看，也并非难到无法承受的地步，多想想，思路贯通之后还是很好理解的。
后记：捷文规范
1.本文成长记录及勘误表
Swift
3.6w
pekonchan
JavaScript
1.7w
crazysunj
Android
ZXing
9439
JavaScript
Visual Studio Code
1.7w
腾讯IVWEB团队
Node.js
JavaScript
3.4w
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ECMAScript 6
15.4w
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VIP.5 如鱼得水
万花过尽知无物 @ 编程之王
