java - FileOutputStream 头指针

Question

我正在寻找 FileOutputStream 是否像我认为的那样工作的确认。我正在下载一个文件，如果我失去了网络连接，我会尝试从中断的地方继续下载。

我尝试这样做的方式是打开 FileOutputStream，而不是附加，然后在偏移量处不写入任何内容。我的问题是这会起作用还是以非附加方式打开它会删除内容？另外，如果我在一个偏移量处写入，它会在后续调用写入时继续在文件中的该位置之后写入吗？

File outFile = new File(outFileName);
FileOutputStream out = new FileOutputStream(outFile);
HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();

long fileSize = connection.getContentLength();
int status = DOWNLOADING;

connection.connect();
InputStream in = connection.getInputStream();
long downloaded = in.skip(outFile.length());

publishProgress(downloaded, fileSize);

try
{
        int read = 0;
        byte buffer[] = new byte[MAX_BUFFER_SIZE];

        // Skip ahead in the out buffer
        out.write(buffer, (int)downloaded, read);

        while(status == DOWNLOADING)
        {
                if(!NetworkUtils.isConnected(_context))
                {
                        // This breaks us out of the doInBackground in the AsyncTask
                        _downloadFailed = true;
                        throw new Exception("Network Connectivity Lost!");
                }

                read = in.read(buffer);

                if(read == -1) 
                {
                        publishProgress(fileSize);
                        break;
                }

                out.write(buffer, 0, read);
                downloaded += read;

                publishProgress(downloaded);
        }
}
finally
{
        out.close();        
        in.close();
        connection.disconnect();
}

Answer 1

您还应该看看 RandomAccessFile 类，它可以让您定位到某个位置并从那里开始写入，而不会截断文件。