使用OkHttp实现下载的进度监听和断点续传

1. 导入依赖包

// retrofit, 基于Okhttp，考虑到项目中经常会用到retrofit，就导入这个了。
compile 'com.squareup.retrofit2:retrofit:2.1.0'
// ButterKnife
compile 'com.jakewharton:butterknife:7.0.1'
//  rxjava 本例中线程切换要用到，代替handler
compile 'io.reactivex:rxjava:1.1.6'
compile 'io.reactivex:rxandroid:1.2.1'

2. 继承ResponseBody，生成带进度监听的ProgressResponseBody

// 参考okhttp的官方demo，此类当中我们主要把注意力放在ProgressListener和read方法中。在这里获取文件总长我写在了构造方法里，这样免得在source的read方法中重复调用或判断。读者也可以根据个人需要定制自己的监听器。
public class ProgressResponseBody extends ResponseBody {

public interface ProgressListener {
void onPreExecute(long contentLength);
void update(long totalBytes, boolean done);
}

private final ResponseBody responseBody;
private final ProgressListener progressListener;
private BufferedSource bufferedSource;

public ProgressResponseBody(ResponseBody responseBody,
ProgressListener progressListener) {
this.responseBody = responseBody;
this.progressListener = progressListener;
if(progressListener!=null){
progressListener.onPreExecute(contentLength());
}
}

@Override
public MediaType contentType() {
return responseBody.contentType();
}

@Override
public long contentLength() {
return responseBody.contentLength();
}

@Override
public BufferedSource source() {
if (bufferedSource == null) {
bufferedSource = Okio.buffer(source(responseBody.source()));
}
return bufferedSource;
}

private Source source(Source source) {
return new ForwardingSource(source) {
long totalBytes = 0L;
@Override
public long read(Buffer sink, long byteCount) throws IOException {
long bytesRead = super.read(sink, byteCount);
// read() returns the number of bytes read, or -1 if this source is exhausted.
totalBytes += bytesRead != -1 ? bytesRead : 0;
if (null != progressListener) {
progressListener.update(totalBytes, bytesRead == -1);
}
return bytesRead;
}
};
}
}

3.创建ProgressDownloader

//带进度监听功能的辅助类
public class ProgressDownloader {

public static final String TAG = "ProgressDownloader";

private ProgressListener progressListener;
private String url;
private OkHttpClient client;
private File destination;
private Call call;

public ProgressDownloader(String url, File destination, ProgressListener progressListener) {
this.url = url;
this.destination = destination;
this.progressListener = progressListener;
//在下载、暂停后的继续下载中可复用同一个client对象
client = getProgressClient();
}
//每次下载需要新建新的Call对象
private Call newCall(long startPoints) {
Request request = new Request.Builder()
.url(url)
.header("RANGE", "bytes=" + startPoints + "-")//断点续传要用到的，指示下载的区间
.build();
return client.newCall(request);
}

public OkHttpClient getProgressClient() {
// 拦截器，用上ProgressResponseBody
Interceptor interceptor = new Interceptor() {
@Override
public Response intercept(Chain chain) throws IOException {
Response originalResponse = chain.proceed(chain.request());
return originalResponse.newBuilder()
.body(new ProgressResponseBody(originalResponse.body(), progressListener))
.build();
}
};

return new OkHttpClient.Builder()
.addNetworkInterceptor(interceptor)
.build();
}

// startsPoint指定开始下载的点
public void download(final long startsPoint) {
call = newCall(startsPoint);
call.enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {

}

@Override
public void onResponse(Call call, Response response) throws IOException {
save(response, startsPoint);
}
});
}

public void pause() {
if(call!=null){
call.cancel();
}
}

private void save(Response response, long startsPoint) {
ResponseBody body = response.body();
InputStream in = body.byteStream();
FileChannel channelOut = null;
// 随机访问文件，可以指定断点续传的起始位置
RandomAccessFile randomAccessFile = null;
try {
randomAccessFile = new RandomAccessFile(destination, "rwd");
//Chanel NIO中的用法，由于RandomAccessFile没有使用缓存策略，直接使用会使得下载速度变慢，亲测缓存下载3.3秒的文件，用普通的RandomAccessFile需要20多秒。
channelOut = randomAccessFile.getChannel();
// 内存映射，直接使用RandomAccessFile，是用其seek方法指定下载的起始位置，使用缓存下载，在这里指定下载位置。
MappedByteBuffer mappedBuffer = channelOut.map(FileChannel.MapMode.READ_WRITE, startsPoint, body.contentLength());
byte[] buffer = new byte[1024];
int len;
while ((len = in.read(buffer)) != -1) {
mappedBuffer.put(buffer, 0, len);
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try {
in.close();
if (channelOut != null) {
channelOut.close();
}
if (randomAccessFile != null) {
randomAccessFile.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}

4. 测试demo

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

public class MainActivity extends AppCompatActivity implements ProgressResponseBody.ProgressListener {

public static final String TAG = "MainActivity";
public static final String PACKAGE_URL = "http://gdown.baidu.com/data/wisegame/df65a597122796a4/weixin_821.apk";
@Bind(R.id.progressBar)
ProgressBar progressBar;
private long breakPoints;
private ProgressDownloader downloader;
private File file;
private long totalBytes;
private long contentLength;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
}

@OnClick({R.id.downloadButton, R.id.cancel_button, R.id.continue_button})
public void onClick(View view) {
switch (view.getId()) {
case R.id.downloadButton:
// 新下载前清空断点信息
breakPoints = 0L;
file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "sample.apk");
downloader = new ProgressDownloader(PACKAGE_URL, file, this);
downloader.download(0L);
break;
case R.id.pause_button:
downloader.pause();
Toast.makeText(this, "下载暂停", Toast.LENGTH_SHORT).show();
// 存储此时的totalBytes，即断点位置。
breakPoints = totalBytes;
break;
case R.id.continue_button:
downloader.download(breakPoints);
break;
}
}

@Override
public void onPreExecute(long contentLength) {
// 文件总长只需记录一次，要注意断点续传后的contentLength只是剩余部分的长度
if (this.contentLength == 0L) {
this.contentLength = contentLength;
progressBar.setMax((int) (contentLength / 1024));
}
}

@Override
public void update(long totalBytes, boolean done) {
// 注意加上断点的长度
this.totalBytes = totalBytes + breakPoints;
progressBar.setProgress((int) (totalBytes + breakPoints) / 1024);
if (done) {
// 切换到主线程
Observable
.empty()
.observeOn(AndroidSchedulers.mainThread())
.doOnCompleted(new Action0() {
@Override
public void call() {
Toast.makeText(MainActivity.this, "下载完成", Toast.LENGTH_SHORT).show();
}
})
.subscribe();
}
}
}