无法从Dropbox下载文件

Question

我正在从Dropbox上传和下载文件。 当我上传文件时，它会正确上传。 当我下载文件并打开它时，该文件是零字节。 有人能告诉我为什么会这样吗？

下载代码：

try {
    File localFile = new File(localFilePath);
    File fileSelected = new File(dropboxPath);

    if (!localFile.exists()) {
        localFile.createNewFile();
    } else {
        //copy(fileSelected, localFile);
        //mApi.copy("/Test/test.png", "/sdcard/testfile.png");

        BufferedInputStream br = null;
        BufferedOutputStream bw = null;
        DropboxInputStream fd;
        try {
            fd = mApi.getFileStream(fileSelected.getPath(), null);
            br = new BufferedInputStream(fd);
            bw = new BufferedOutputStream(new FileOutputStream(localFile));

            byte[] buffer = new byte[4096];
            int read;
            while (true) {
                read = br.read(buffer);
                if (read <= 0) {
                    break;
                }
                bw.write(buffer, 0, read);
            }    
        } catch (DropboxException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (bw != null) {
                try {
                    bw.close();
                    if (br != null) {
                        br.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }/*
    else {
        showToast("File already exists");
    }*/
} 
catch (IOException e) {
    showToast("Exception");
    e.printStackTrace();
}
catch (Exception e) {
    showToast("Exception");
    e.printStackTrace();
}

Answer 1

/*
 * Copyright (c) 2010-11 Dropbox, Inc.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */


package codelynks.easydropbox;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.widget.Toast;

import com.dropbox.client2.DropboxAPI;
import com.dropbox.client2.DropboxAPI.Entry;
import com.dropbox.client2.ProgressListener;
import com.dropbox.client2.exception.DropboxException;
import com.dropbox.client2.exception.DropboxIOException;
import com.dropbox.client2.exception.DropboxParseException;
import com.dropbox.client2.exception.DropboxPartialFileException;
import com.dropbox.client2.exception.DropboxServerException;
import com.dropbox.client2.exception.DropboxUnlinkedException;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Here we show getting metadata for a directory and downloading a file in a
 * background thread, trying to show typical exception handling and flow of
 * control for an app that downloads a file from Dropbox.
 */

public class Download extends AsyncTask<Void, Long, Boolean> {


    private Context mContext;
    private final ProgressDialog mDialog;
    private DropboxAPI<?> mApi;
    private String mPath;

    private Drawable mDrawable;

    private FileOutputStream mFos;

    private boolean mCanceled;
    private Long mFileLen;
    private String mErrorMsg;
    private String mDownloadpath;

    // Note that, since we use a single file name here for simplicity, you
    // won't be able to use this code for two simultaneous downloads.
    private final static String IMAGE_FILE_NAME = "dbroulette.png";

    public Download(Context context, DropboxAPI<?> api,
                    String dropboxPath, String downloadpath) {
        // We set the context this way so we don't accidentally leak activities
        mContext = context.getApplicationContext();

        mApi = api;
        mPath = dropboxPath;
        mDownloadpath = downloadpath;
        mDialog = new ProgressDialog(context);
        mDialog.setMax(100);
        mDialog.setMessage("Downloading File");
        mDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        mDialog.setProgress(0);

        mDialog.setButton(ProgressDialog.BUTTON_POSITIVE, "Cancel", new OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                mCanceled = true;
                mErrorMsg = "Canceled";

                // This will cancel the getThumbnail operation by closing
                // its stream
                if (mFos != null) {
                    try {
                        mFos.close();
                    } catch (IOException e) {
                    }
                }
            }
        });

        mDialog.show();
        mDialog.setCanceledOnTouchOutside(false);
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        try {
            if (mCanceled) {
                return false;
            }

            // Get the metadata for a directory
            Entry dirent = mApi.metadata(mPath, 1000, null, true, null);

            if (dirent.isDir) {
                // It's not a directory, or there's nothing in it
                mErrorMsg = "Directory Can't be download";
                return false;
            }


            if (mCanceled) {
                return false;
            }

            try {
                mFos = new FileOutputStream(mDownloadpath);
            } catch (FileNotFoundException e) {
                mErrorMsg = "Couldn't create a local file to store the image";
                return false;
            }
            mApi.getFile(mPath, null, mFos, new ProgressListener() {
                @Override
                public long progressInterval() {
                    return 500;
                }

                @Override
                public void onProgress(long arg0, long arg1) {
                    mFileLen = arg1;//Total File Length
                    publishProgress(arg0);//Downloaded File Length
                }
            });


            if (mCanceled) {
                return false;
            }


            // We must have a legitimate picture
            return true;

        } catch (DropboxUnlinkedException e) {
            // The AuthSession wasn't properly authenticated or user unlinked.
        } catch (DropboxPartialFileException e) {
            // We canceled the operation
            mErrorMsg = "Download canceled";
        } catch (DropboxServerException e) {
            // Server-side exception.  These are examples of what could happen,
            // but we don't do anything special with them here.
            if (e.error == DropboxServerException._304_NOT_MODIFIED) {
                // won't happen since we don't pass in revision with metadata
            } else if (e.error == DropboxServerException._401_UNAUTHORIZED) {
                // Unauthorized, so we should unlink them.  You may want to
                // automatically log the user out in this case.
            } else if (e.error == DropboxServerException._403_FORBIDDEN) {
                // Not allowed to access this
            } else if (e.error == DropboxServerException._404_NOT_FOUND) {
                // path not found (or if it was the thumbnail, can't be
                // thumbnailed)
            } else if (e.error == DropboxServerException._406_NOT_ACCEPTABLE) {
                // too many entries to return
            } else if (e.error == DropboxServerException._415_UNSUPPORTED_MEDIA) {
                // can't be thumbnailed
            } else if (e.error == DropboxServerException._507_INSUFFICIENT_STORAGE) {
                // user is over quota
            } else {
                // Something else
            }
            // This gets the Dropbox error, translated into the user's language
            mErrorMsg = e.body.userError;
            if (mErrorMsg == null) {
                mErrorMsg = e.body.error;
            }
        } catch (DropboxIOException e) {
            // Happens all the time, probably want to retry automatically.
            mErrorMsg = "Network error.  Try again.";
        } catch (DropboxParseException e) {
            // Probably due to Dropbox server restarting, should retry
            mErrorMsg = "Dropbox error.  Try again.";
        } catch (DropboxException e) {
            // Unknown error
            mErrorMsg = "Unknown error.  Try again.";
        }
        return false;
    }

    @Override
    protected void onProgressUpdate(Long... progress) {
        int percent = (int) (100.0 * (double) progress[0] / mFileLen + 0.5);
        mDialog.setProgress(percent);
    }

    @Override
    protected void onPostExecute(Boolean result) {
        mDialog.dismiss();
        if (result) {
            showToast("Downloading Finished");
            // Set the image now that we have it
            //mView.setImageDrawable(mDrawable);
        } else {
            // Couldn't download it, so show an error
            showToast(mErrorMsg);
        }
    }

    private void showToast(String msg) {
        Toast error = Toast.makeText(mContext, msg, Toast.LENGTH_LONG);
        error.show();
    }


}

调用后面的后台线程

Download download = new Download(context, mApi, drop_box_file_path, sdcard_path_to_store);
        download.execute();

其中，mApi是DropboxAPI的参考