先附上流程图
1.入口DownLoadManager.download()
/**
*
* @param request 请求实体参数Entity
* @param tag 下载地址
* @param callBack 返回给调用的CollBack
*/
public void download(DownloadRequest request, String tag, CallBack callBack) {
final String key = createKey(tag);
if (check(key)) {
// 请求的响应 需要状态传递类 以及对应的回调
DownloadResponse response = new DownloadResponseImpl(mDelivery, callBack);
// 下载器 需要线程池 数据库管理者 对应的url key值 之后回调给自己
Downloader downloader = new DownloaderImpl(request, response,
mExecutorService, mDBManager, key, mConfig, this);
mDownloaderMap.put(key, downloader);
//开始下载
downloader.start();
}
}
复制代码DownloadResponseImpl 下载响应需要把本身的下载事件回调给调用者，由于下载是在子线程里面的，所以专门搞了一个下载状态的传递类
DownLoaderImpl 下载器 需要的参数就比较多了，请求实体，对应的下载响应，线程池，数据库管理器，url的hash值，对应的配置，还有下载的回调
加入进LinkedHashMap 做一个有序的存储
之后调用下载器的start方法
2.开始下载 start
@Override
public void start() {
//修改为Started状态
mStatus = DownloadStatus.STATUS_STARTED;
//CallBack 回调给调用者
mResponse.onStarted();
// 连接获取是否支持多线程下载
connect();
}
/**
* 执行连接任务
*/
private void connect() {
mConnectTask = new ConnectTaskImpl(mRequest.getUri(), this);
mExecutor.execute(mConnectTask);
}
复制代码在正式下载之前需要确定后台是否支持断点下载，所以才有先执行这个ConnectTaskImpl 连接任务
3.ConnectTaskImpl 连接任务
@Override
public void run() {
// 设置为后台线程
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
//修改连接中状态
mStatus = DownloadStatus.STATUS_CONNECTING;
//回调给调用者
mOnConnectListener.onConnecting();
try {
//执行连接方法
executeConnection();
} catch (DownloadException e) {
handleDownloadException(e);
}
}
/**
*
* @throws DownloadException
*/
private void executeConnection() throws DownloadException {
mStartTime = System.currentTimeMillis();
HttpURLConnection httpConnection = null;
final URL url;
try {
url = new URL(mUri);
} catch (MalformedURLException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "Bad url.", e);
}
try {
httpConnection = (HttpURLConnection) url.openConnection();
httpConnection.setConnectTimeout(Constants.HTTP.CONNECT_TIME_OUT);
httpConnection.setReadTimeout(Constants.HTTP.READ_TIME_OUT);
httpConnection.setRequestMethod(Constants.HTTP.GET);
httpConnection.setRequestProperty("Range", "bytes=" + 0 + "-");
final int responseCode = httpConnection.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
//后台不支持断点下载,启用单线程下载
parseResponse(httpConnection, false);
} else if (responseCode == HttpURLConnection.HTTP_PARTIAL) {
//后台支持断点下载,启用多线程下载
parseResponse(httpConnection, true);
} else {
throw new DownloadException(DownloadStatus.STATUS_FAILED,
"UnSupported response code:" + responseCode);
}
} catch (ProtocolException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "Protocol error", e);
} catch (IOException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "IO error", e);
} finally {
if (httpConnection != null) {
httpConnection.disconnect();
}
}
}
private void parseResponse(HttpURLConnection httpConnection, boolean isAcceptRanges)
throws DownloadException {
final long length;
//header获取length
String contentLength = httpConnection.getHeaderField("Content-Length");
if (TextUtils.isEmpty(contentLength) || contentLength.equals("0") || contentLength
.equals("-1")) {
//判断后台给你length,为null 0,-1,从连接中获取
length = httpConnection.getContentLength();
} else {
//直接转化
length = Long.parseLong(contentLength);
}
if (length <= 0) {
//抛出异常数据
throw new DownloadException(DownloadStatus.STATUS_FAILED, "length <= 0");
}
//判断是否取消和暂停
checkCanceledOrPaused();
//Successful
mStatus = DownloadStatus.STATUS_CONNECTED;
//获取时间差
final long timeDelta = System.currentTimeMillis() - mStartTime;
//回调给调用者
mOnConnectListener.onConnected(timeDelta, length, isAcceptRanges);
}
private void checkCanceledOrPaused() throws DownloadException {
if (isCanceled()) {
// cancel
throw new DownloadException(DownloadStatus.STATUS_CANCELED, "Connection Canceled!");
} else if (isPaused()) {
// paused
throw new DownloadException(DownloadStatus.STATUS_PAUSED, "Connection Paused!");
}
}
//统一执行对应的异常信息
private void handleDownloadException(DownloadException e) {
switch (e.getErrorCode()) {
case DownloadStatus.STATUS_FAILED:
synchronized (mOnConnectListener) {
mStatus = DownloadStatus.STATUS_FAILED;
mOnConnectListener.onConnectFailed(e);
}
break;
case DownloadStatus.STATUS_PAUSED:
synchronized (mOnConnectListener) {
mStatus = DownloadStatus.STATUS_PAUSED;
mOnConnectListener.onConnectPaused();
}
break;
case DownloadStatus.STATUS_CANCELED:
synchronized (mOnConnectListener) {
mStatus = DownloadStatus.STATUS_CANCELED;
mOnConnectListener.onConnectCanceled();
}
break;
default:
throw new IllegalArgumentException("Unknown state");
}
}
复制代码HttpURLConnection.HTTP_OK 不支持断点下载 使用单线程下载
HttpURLConnection.HTTP_PARTIAL 支持断点下载 使用多线程下载
如果成功就会回调到OnConnectListener.onConnected(timeDelta, length, isAcceptRanges)方法中
回到下载器查看onConnected方法
4.查看下载器的onConnected（）
@Override
public void onConnected(long time, long length, boolean isAcceptRanges) {
if (mConnectTask.isCanceled()) {
//连接取消
onConnectCanceled();
} else {
mStatus = DownloadStatus.STATUS_CONNECTED;
//回调给你响应连接成功状态
mResponse.onConnected(time, length, isAcceptRanges);
mDownloadInfo.setAcceptRanges(isAcceptRanges);
mDownloadInfo.setLength(length);
//真正开始下载
download(length, isAcceptRanges);
}
}
@Override
public void onConnectCanceled() {
deleteFromDB();
deleteFile();
mStatus = DownloadStatus.STATUS_CANCELED;
mResponse.onConnectCanceled();
onDestroy();
}
@Override
public void onDestroy() {
// trigger the onDestroy callback tell download manager
mListener.onDestroyed(mTag, this);
}
复制代码根据状态来处理，isCanceled() 删除数据库里面的数据，删除文件，更改为取消状态状态
未取消，进去下载download
5.下载文件download方法
/**
* 下载开始
* @param length 设置下载的长度
* @param acceptRanges 是否支持断点下载
*/
private void download(long length, boolean acceptRanges) {
mStatus = DownloadStatus.STATUS_PROGRESS;
initDownloadTasks(length, acceptRanges);
//开始下载任务
for (DownloadTask downloadTask : mDownloadTasks) {
mExecutor.execute(downloadTask);
}
}
/**
* 初始化下载任务
* @param length
* @param acceptRanges
*/
private void initDownloadTasks(long length, boolean acceptRanges) {
mDownloadTasks.clear();
if (acceptRanges) {
List threadInfos = getMultiThreadInfos(length);
// init finished
int finished = 0;
for (ThreadInfo threadInfo : threadInfos) {
finished += threadInfo.getFinished();
}
mDownloadInfo.setFinished(finished);
for (ThreadInfo info : threadInfos) {
//开始多线程下载
mDownloadTasks.add(new MultiDownloadTask(mDownloadInfo, info, mDBManager, this));
}
} else {
//单线程下载不需要保存进度信息
ThreadInfo info = getSingleThreadInfo();
mDownloadTasks.add(new SingleDownloadTask(mDownloadInfo, info, this));
}
}
//TODO
private List getMultiThreadInfos(long length) {
// init threadInfo from db
final List threadInfos = mDBManager.getThreadInfos(mTag);
if (threadInfos.isEmpty()) {
final int threadNum = mConfig.getThreadNum();
for (int i = 0; i < threadNum; i++) {
// calculate average
final long average = length / threadNum;
final long start = average * i;
final long end;
if (i == threadNum - 1) {
end = length;
} else {
end = start + average - 1;
}
ThreadInfo threadInfo = new ThreadInfo(i, mTag, mRequest.getUri(), start, end, 0);
threadInfos.add(threadInfo);
}
}
return threadInfos;
}
//单线程数据
private ThreadInfo getSingleThreadInfo() {
ThreadInfo threadInfo = new ThreadInfo(0, mTag, mRequest.getUri(), 0);
return threadInfo;
}
复制代码 根据connected返回的数据判断是否支持断点下载，支持acceptRanges 就调用getMultiThreadInfos来组装多线程下载数据，多线程需要初始化下载的进度信息，二单线程getSingleThreadInfo自己组装一个简单的就可以了
6.执行DownloadTaskImpl
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
// 插入数据库
insertIntoDB(mThreadInfo);
try {
mStatus = DownloadStatus.STATUS_PROGRESS;
executeDownload();
//根据回调对象，加锁
synchronized (mOnDownloadListener) {
//没出异常就代表下载完成了
mStatus = DownloadStatus.STATUS_COMPLETED;
mOnDownloadListener.onDownloadCompleted();
}
} catch (DownloadException e) {
handleDownloadException(e);
}
}
/**
* 开始下载数据
*/
private void executeDownload() throws DownloadException {
final URL url;
try {
url = new URL(mThreadInfo.getUri());
} catch (MalformedURLException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "Bad url.", e);
}
HttpURLConnection httpConnection = null;
try {
//设置http连接信息
httpConnection = (HttpURLConnection) url.openConnection();
httpConnection.setConnectTimeout(HTTP.CONNECT_TIME_OUT);
httpConnection.setReadTimeout(HTTP.READ_TIME_OUT);
httpConnection.setRequestMethod(HTTP.GET);
//设置header数据，断点下载设置关键
setHttpHeader(getHttpHeaders(mThreadInfo), httpConnection);
final int responseCode = httpConnection.getResponseCode();
if (responseCode == getResponseCode()) {
//下载数据
transferData(httpConnection);
} else {
throw new DownloadException(DownloadStatus.STATUS_FAILED,
"UnSupported response code:" + responseCode);
}
} catch (ProtocolException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "Protocol error", e);
} catch (IOException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "IO error", e);
} finally {
if (httpConnection != null) {
httpConnection.disconnect();
}
}
}
/**
* 设置header数据
*
* @param headers header元数据
*/
private void setHttpHeader(Map headers, URLConnection connection) {
if (headers != null) {
for (String key : headers.keySet()) {
connection.setRequestProperty(key, headers.get(key));
}
}
}
/**
* 下载数据
*/
private void transferData(HttpURLConnection httpConnection) throws DownloadException {
InputStream inputStream = null;
RandomAccessFile raf = null;
try {
try {
inputStream = httpConnection.getInputStream();
} catch (IOException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "http get inputStream error", e);
}
//获取下载的偏移量
final long offset = mThreadInfo.getStart() + mThreadInfo.getFinished();
try {
//设置偏移量
raf = getFile(mDownloadInfo.getDir(), mDownloadInfo.getName(), offset);
} catch (IOException e) {
throw new DownloadException(DownloadStatus.STATUS_FAILED, "File error", e);
}
//开始写入数据
transferData(inputStream, raf);
} finally {
try {
IOCloseUtils.close(inputStream);
IOCloseUtils.close(raf);
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 写入数据
*/
private void transferData(InputStream inputStream, RandomAccessFile raf)
throws DownloadException {
final byte[] buffer = new byte[1024 * 8];
while (true) {
checkPausedOrCanceled();
int len = -1;
try {
len = inputStream.read(buffer);
if (len == -1) {
break;
}
raf.write(buffer, 0, len);
//设置下载的信息
mThreadInfo.setFinished(mThreadInfo.getFinished() + len);
synchronized (mOnDownloadListener) {
mDownloadInfo.setFinished(mDownloadInfo.getFinished() + len);
//回调进度
mOnDownloadListener
.onDownloadProgress(mDownloadInfo.getFinished(), mDownloadInfo.getLength());
}
} catch (IOException e) {
//更新数据库
updateDB(mThreadInfo);
throw new DownloadException(DownloadStatus.STATUS_FAILED, e);
}
}
}
复制代码 断点下载的关键是在header头信息里面添加已经下载length ，下载数据也是从下载的length点开始写入数据，写入数据，每个线程在对应的片段里面下载对应的数据，后期使用RandomAccessFile组装起来，合成一个文件
7.多线程下载时的header数据，以及RandomAccessFile组装
@Override
protected Map getHttpHeaders(ThreadInfo info) {
Map headers = new HashMap();
//计算开始和结束的位置
long start = info.getStart() + info.getFinished();
long end = info.getEnd();
headers.put("Range", "bytes=" + start + "-" + end);
return headers;
}
@Override
protected RandomAccessFile getFile(File dir, String name, long offset) throws IOException {
File file = new File(dir, name);
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置偏移量
raf.seek(offset);
return raf;
}
复制代码 8.单线程下载
@Override
protected Map getHttpHeaders(ThreadInfo info) {
// simply return null
return null;
}
@Override
protected RandomAccessFile getFile(File dir, String name, long offset) throws IOException {
File file = new File(dir, name);
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
raf.seek(0);
return raf;
}
复制代码 单线程下载不需要偏移量
具体可以查看github.com/lizubing199…