最近总结一下了一下之前学过以及用到过得功能，整理了一个基于Ok+Rxjava实现断点续传下载的demo。下面先给大家展示一下使用效果吧。
说下我的大致思路吧:根据文件下载url按照自己定义的规则生成文件名，判断本地同路径下是否存在此文件，如果存在，文件大小与服务器上获取的文件大小一致的情况下，则生成新的文件名重新下载；如果文件比服务器获取的文件大小小，则执行断点下载，从本地文件长度处开始下载。如果文件不存在，则从0字节开始下载。
DownloadSubscribe（被观察者）中执行下载存入本地操作
核心还是：addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)
DownLoadObserver（观察者）通过onnext(DownloadInfo downloadInfo)方法回调下载进度
下面上主要代码：
/**
* 开始下载
* @param url 下载请求的网址
* @param downFileCallback 用来回调的接口
*/
public void download(final String url, final DownFileCallback downFileCallback) {
if (url == null || downCalls.get(url) != null) {
return;
}
Observable.just(url)
.filter(new Predicate<String>() {
@Override
public boolean test(String s) throws Exception {
//过滤条件 若map中存在，则这次不下载
return !downCalls.containsKey(s);
}
})
.flatMap(new Function<String, ObservableSource<DownloadInfo>>() {
@Override
public ObservableSource<DownloadInfo> apply(String s) throws Exception {
//创建下载实体类
return Observable.just(createDownInfo(s));
}
})
.map(new Function<DownloadInfo, DownloadInfo>() {
@Override
public DownloadInfo apply(DownloadInfo s) throws Exception {
//根据本地是否存在此文件，来设置文件名及文件初始下载大小
return getRealFileName(s);
}
})
.flatMap(new Function<DownloadInfo, ObservableSource<DownloadInfo>>() {
@Override
public ObservableSource<DownloadInfo> apply(DownloadInfo downloadInfo) throws Exception {
//创建被观察者
return Observable.create(new DownloadSubscribe(downloadInfo));
}
})//下载
.observeOn(AndroidSchedulers.mainThread())//在主线程回调
.subscribeOn(Schedulers.io())//在子线程执行
.subscribe(new DownLoadObserver() {//添加观察者
@Override
public void onNext(DownloadInfo downloadInfo) {
super.onNext(downloadInfo);
downFileCallback.onProgress(downloadInfo.getTotal(), downloadInfo.getProgress());
}
@Override
public void onError(Throwable e) {
super.onError(e);
if (!(e instanceof SocketException)) {
downFileCallback.onFail(e.getMessage());
}
}
@Override
public void onComplete() {
downFileCallback.onSuccess(url);
}
});
}
/**
* 根据url暂停下载操作
* @param url
*/
public void cancel(String url) {
Call call = downCalls.get(url);
if (call != null) {
call.cancel();//取消
}
downCalls.remove(url);
}
/**
* 创建被观察者DownloadSubscribe
*/
private class DownloadSubscribe implements ObservableOnSubscribe<DownloadInfo> {
private DownloadInfo downloadInfo;
public DownloadSubscribe(DownloadInfo downloadInfo) {
this.downloadInfo = downloadInfo;
}
@Override
public void subscribe(ObservableEmitter<DownloadInfo> e) throws Exception {
String url = downloadInfo.getUrl();
long downloadLength = downloadInfo.getProgress();//已经下载好的长度
long contentLength = downloadInfo.getTotal();//文件的总长度
//初始进度信息
e.onNext(downloadInfo);
Request request = new Request.Builder()
//断点续传的核心
.addHeader("RANGE", "bytes=" + downloadLength + "-" + contentLength)
.url(url)
.build();
Call call = mClient.newCall(request);
//根据下载url，把call存放在map中，取消的时候就可以通过call.cancle()来实现
downCalls.put(url, call);
Response response = call.execute();
File file = new File(getTemporaryPath(), downloadInfo.getFileName());
InputStream is = null;
FileOutputStream fileOutputStream = null;
try {
is = response.body().byteStream();
fileOutputStream = new FileOutputStream(file, true);
byte[] buffer = new byte[2048];//缓冲数组2kB
int len;
while ((len = is.read(buffer)) != -1) {
fileOutputStream.write(buffer, 0, len);
downloadLength += len;
downloadInfo.setProgress(downloadLength);
e.onNext(downloadInfo);
}
fileOutputStream.flush();
downCalls.remove(url);
} finally {
//关闭IO流
IOUtil.closeAll(is, fileOutputStream);
}
e.onComplete();//完成
}
}
/**
* 从服务器获取文件长度
*
* @param downloadUrl
* @return
*/
private long getContentLength(String downloadUrl) {
Request request = new Request.Builder()
.url(downloadUrl)
.build();
try {
Response response = mClient.newCall(request).execute();
if (response != null && response.isSuccessful()) {
long contentLength = response.body().contentLength();
response.close();
return contentLength == 0 ? DownloadInfo.TOTAL_ERROR : contentLength;
}
} catch (IOException e) {
e.printStackTrace();
}
return DownloadInfo.TOTAL_ERROR;
}
从服务器获取文件长度的时候注意一下，Android P之后，也就是api 28以上禁止明文网络传输。需要在你的AndroidManifest中的application标签中声明"android:usesCleartextTraffic="true",允许应用进行明文传输。
使用方法：首先要获取sd卡权限
DownloadManager.getInstance().downloadPath(本地存在地址).download(url1, new DownFileCallback() {
@Override
public void onProgress(long totalSize, long downSize) {
progress1.setMax((int) totalSize);
progress1.setProgress((int) downSize);
}
@Override
public void onSuccess(String url) {
Toast.makeText(MainActivity.this, url1 + "下载完成", Toast.LENGTH_SHORT).show();
}
@Override
public void onFail(String msg) {
Toast.makeText(MainActivity.this, url1 + "下载失败", Toast.LENGTH_SHORT).show();
}
});
好了今天就到这里，希望能帮到大家，这对我来说也是一种加深印象的笔记，
下载地址demo
git地址：DownloadManager 欢迎star
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
