okhttp下载文件断点下载暂停下载

以下是使用OkHttp实现文件下载的示例代码，其中包括断点下载和暂停下载的功能：

public class DownloadManager {
    private static final String TAG = "DownloadManager";
    private static final int DEFAULT_TIMEOUT = 10;
    private static DownloadManager mInstance;
    private OkHttpClient mOkHttpClient;
    private Handler mHandler;

    private DownloadManager() {
        mOkHttpClient = new OkHttpClient.Builder()
                .connectTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS)
                .build();
        mHandler = new Handler(Looper.getMainLooper());
    }

    public static DownloadManager getInstance() {
        if (mInstance == null) {
            synchronized (DownloadManager.class) {
                if (mInstance == null) {
                    mInstance = new DownloadManager();
                }
            }
        }
        return mInstance;
    }

    public void download(final String url, final String destFileDir, final DownloadListener listener) {
        final Request request = new Request.Builder()
                .url(url)
                .build();
        final Call call = mOkHttpClient.newCall(request);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                handleError(call, e, listener);
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                if (response.isSuccessful()) {
                    handleResponse(response, destFileDir, listener);
                } else {
                    handleError(call, new IOException("Unexpected code " + response), listener);
                }
            }
        });
    }

    private void handleResponse(Response response, String destFileDir, DownloadListener listener) {
        InputStream is = null;
        byte[] buf = new byte[2048];
        int len;
        FileOutputStream fos = null;
        try {
            is = response.body().byteStream();
            final long total = response.body().contentLength();
            File dir = new File(destFileDir);
            if (!dir.exists()) {
                dir.mkdirs();
            }
            File file = new File(dir, getFileName(response));
            fos = new FileOutputStream(file);
            long sum = 0;
            while ((len = is.read(buf)) != -1) {
                fos.write(buf, 0, len);
                sum += len;
                final long finalSum = sum;
                mHandler.post(new Runnable() {
                    @Override
                    public void run() {
                        listener.onProgress(finalSum * 1.0f / total);
                    }
                });
            }
            fos.flush();
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    listener.onSuccess();
                }
            });
        } catch (Exception e) {
            handleError(response.request().call(), e, listener);
        } finally {
            try {
                if (is != null) is.close();
            } catch (IOException e) {
            }
            try {
                if (fos != null) fos.close();
            } catch (IOException e) {
            }
        }
    }

    private void handleError(final Call call, final Exception e, final DownloadListener listener) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                listener.onFailure(e);
            }
        });
        if (call != null) {
            call.cancel();
        }
    }

    private String getFileName(Response response) {
        String fileName = "";
        String disposition = response.header("Content-Disposition");
        if (!TextUtils.isEmpty(disposition)) {
            int index = disposition.indexOf("filename=");
            if (index > 0) {
                fileName = disposition.substring(index + 10, disposition.length() - 1);
            }
        }
        if (TextUtils.isEmpty(fileName)) {
            fileName = System.currentTimeMillis() + ".apk";
        }
        return fileName;
    }

    public interface DownloadListener {
        void onProgress(float progress);

        void onSuccess();

        void onFailure(Exception e);
    }
}

使用示例：

DownloadManager.getInstance().download(url, destFileDir, new DownloadManager.DownloadListener() {
    @Override
    public void onProgress(float progress) {
        // 更新进度条
    }

    @Override
    public void onSuccess() {
        // 下载成功
    }

    @Override
    public void onFailure(Exception e) {
        // 下载失败
    }
});

暂停下载可以通过调用`Call.cancel()`方法实现，断点下载可以通过在请求头中添加`Range`字段实现。相关代码如下：

public void download(final String url, final String destFileDir, final DownloadListener listener) {
    final Request request = new Request.Builder()
            .url(url)
            .build();
    final Call call = mOkHttpClient.newCall(request);
    call.enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            handleError(call, e, listener);
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (response.isSuccessful()) {
                handleResponse(response, destFileDir, listener);
            } else {
                handleError(call, new IOException("Unexpected code " + response), listener);
            }
        }
    });
}

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

public void resume(final String url, final String destFileDir, final DownloadListener listener) {
    final File file = new File(destFileDir, getFileName(url));
    final long currentLength = file.length();
    final Request request = new Request.Builder()
            .url(url)
            .addHeader("RANGE", "bytes=" + currentLength + "-")
            .build();
    final Call call = mOkHttpClient.newCall(request);
    call.enqueue(new Callback() {
        @Override
        public void onFailure(Call call, IOException e) {
            handleError(call, e, listener);
        }

        @Override
        public void onResponse(Call call, Response response) throws IOException {
            if (response.isSuccessful()) {
                handleResponse(response, file.getAbsolutePath(), listener);
            } else {
                handleError(call, new IOException("Unexpected code " + response), listener);
            }
        }
    });
}

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