Android启动service下载失败后stopService，重新启动service下载出现问题

   在Android启用service后台下载，使用异步线程进行下载，下载失败时，关掉service。在重新下载时，重新启动service，启动新的异步线程进行下载；因为上一次下载失败只是启动了停止了service，但上一个异步线程任务还在继续运行，此时又有新的线程任务运行，导致两个不同的线程访问同一段代码，导致出错。解决办法是，上一次下载失败时，除了关闭service也要cancel掉异步下载任务的request。

OkHttpClient mOkHttpClient = new OkHttpClient();

// 启动异步线程访问网络
public static void enqueue(Request request, Callback responseCallback, GetCallCancelCallback callback) {
        Call call = mOkHttpClient.newCall(request);
        callback.getCall(call);
        call.enqueue(responseCallback);
    }

一下是下载接口，传入下载的URL，存储路径，以及回调。

// 下载接口
public static void download(String downloadUrl, final String distPath, final DownloadCallback callback) {
        Request request = new Request.Builder().url(downloadUrl).build();
        enqueue(request, new Callback() {
            @Override
            public void onResponse(Response response) {
                if (response.isSuccessful()) {
                    try {
                        InputStream is = response.body().byteStream();
                        long totalSize = response.body().contentLength();
                        FileOutputStream fos = new FileOutputStream(distPath);
                        int len = 0;
                        long downloadSize = 0;
                        byte[] buffer = new byte[1024 * 8];
                        while ((len = is.read(buffer)) != -1) {
                            downloadSize += len;
                            callback.onDownload(downloadSize, totalSize);
                            fos.write(buffer, 0, len);
                        }
                        if (callback != null) {
                            callback.onSuccess(null);
                            return;
                        }
                    } catch (IOException e) {
                        if (callback != null) {
                            callback.onFail(null);
                        }
                    }
                }
                if (callback != null) {
                    callback.onFail(null);
                }
            }

            @Override
            public void onFailure(Request request, IOException arg1) {
                if (callback != null) {
                    callback.onFail(null);
                }
            }
        }, new GetCallCancelCallback() {
            @Override
            public void getCall(Call call) {
                callback.onGetCall(call);  //回调，取得此时的Call
            }
        });
    }

// service中的关键代码
download(url, filePath, new NetUtils.DownloadCallback() {
                @Override
                public void onSuccess(String result) {

                     downloadFinish();
                }

                @Override
                public void onDownload(final long downloadSize, final long totalSize) {
                   
                    mHandler.post(new Runnable() {
                        @Override
                        public void run() {
                            EventBus.getDefault().post(new DownloadProgressEvent(downloadSize / 1024, totalSize / 1024));
                        }
                    });
                }

                @Override
                public void onFail(String errorInfo) {
                    //删掉该文件
                    LogUtils.error("onDowloadFail", "onDowloadFail");
                    File file = new File(filePath);
                    if (file.exists()) {
                        file.delete();
                    }

                  
                    downloadFinish();
                }

                @Override
                public void onTimeout() {

                    downloadFinish();
                }

                @Override
                public void onGetCall(Call call) {
                    setCall(call);
                }
            });

// 关闭service，取消线程中的下载任务
private void downloadFinish() {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                isRunning = false;
                LogUtils.error("Service", mCall.toString());
                if (mCall != null) {
                    mCall.cancel(); // 取消当前的request
                }
                LogUtils.error("Service", "stop");
                stopSelf();
            }
        });

    }