使用OkHttp實現下載的進度監聽和斷點續傳

1. 匯入依賴包

// retrofit, 基於Okhttp，考慮到專案中經常會用到retrofit，就匯入這個了。
    compile 'com.squareup.retrofit2:retrofit:2.1.0'
// ButterKnife
    compile 'com.jakewharton:butterknife:7.0.1'
//  rxjava 本例中執行緒切換要用到，代替handler
    compile 'io.reactivex:rxjava:1.1.6'
    compile 'io.reactivex:rxandroid:1.2.1'

2. 繼承ResponseBody，生成帶進度監聽的ProgressResponseBody

// 參考okhttp的官方demo，此類當中我們主要把注意力放在ProgressListener和read方法中。在這裡獲取檔案總長我寫在了構造方法裡，這樣免得在source的read方法中重複呼叫或判斷。讀者也可以根據個人需要定製自己的監聽器。
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.建立ProgressDownloader

//帶進度監聽功能的輔助類
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;
        //在下載、暫停後的繼續下載中可複用同一個client物件
        client = getProgressClient();
    }
    //每次下載需要新建新的Call物件
    private Call newCall(long startPoints) {
        Request request = new Request.Builder()
                .url(url)
                .header("RANGE", "bytes=" + startPoints + "-")//斷點續傳要用到的，指示下載的區間
                .build();
        return client.newCall(request);
    }

    public OkHttpClient getProgressClient() {
    // 攔截器，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指定開始下載的點
    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;
        // 隨機訪問檔案，可以指定斷點續傳的起始位置
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile(destination, "rwd");
            //Chanel NIO中的用法，由於RandomAccessFile沒有使用快取策略，直接使用會使得下載速度變慢，親測快取下載3.3秒的檔案，用普通的RandomAccessFile需要20多秒。
            channelOut = randomAccessFile.getChannel();
            // 記憶體對映，直接使用RandomAccessFile，是用其seek方法指定下載的起始位置，使用快取下載，在這裡指定下載位置。
            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. 測試demo

清單檔案中新增網路許可權和檔案訪問許可權

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

MainActivity

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:
            // 新下載前清空斷點資訊
                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, "下載暫停", Toast.LENGTH_SHORT).show();
                // 儲存此時的totalBytes，即斷點位置。
                breakPoints = totalBytes;
                break;
            case R.id.continue_button:
                downloader.download(breakPoints);
                break;
        }
    }

    @Override
    public void onPreExecute(long contentLength) {
        // 檔案總長只需記錄一次，要注意斷點續傳後的contentLength只是剩餘部分的長度
        if (this.contentLength == 0L) {
            this.contentLength = contentLength;
            progressBar.setMax((int) (contentLength / 1024));
        }
    }

    @Override
    public void update(long totalBytes, boolean done) {
        // 注意加上斷點的長度
        this.totalBytes = totalBytes + breakPoints;
        progressBar.setProgress((int) (totalBytes + breakPoints) / 1024);
        if (done) {
        // 切換到主執行緒
            Observable
                    .empty()
                    .observeOn(AndroidSchedulers.mainThread())
                    .doOnCompleted(new Action0() {
                        @Override
                        public void call() {
                            Toast.makeText(MainActivity.this, "下載完成", Toast.LENGTH_SHORT).show();
                        }
                    })
                    .subscribe();
        }
    }
}

最後是動態效果圖