如何在Java中找到ReadableByteChannel的大小? [英] How to find the size of a ReadableByteChannel in Java?

问题描述

我正在使用Java的Channel类将blob从数据库转换为PDF.使用频道的

I am converting a blob from a database into a PDF, using Java's Channel classes. When using a Channel's transferFrom( ) method, you are supposed to specify the maximum number of bytes to be transferred.

当ReadableByteChannels没有像其他Channels一样具有size()方法时，应该如何找到最大字节数?

How are you supposed to find this maximum number of bytes when ReadableByteChannels don't have a size( ) method like other Channels?

由于ReadableByteChannel没有size()方法，因此它不是该作业的正确工具吗?我只是在使用Long.MAX_VALUE，看起来不太正确.

Is a ReadableByteChannel not the right tool for the job since it doesn't have a size( ) method? I'm just using Long.MAX_VALUE which doesn't seem right.

示例代码:

// Get the blob in an InputStream
InputStream inStream = rs.getBinaryStream("SomeBlob");

// Create a ReadableByteChannel from that InputStream
ReadableByteChannel rbc = Channels.newChannel(inStream);

// Make a FileOutputStream to write the PDF From
FileOutputStream outStream = new FileOutputStream("MyPDF.PDF");
outStream.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);

// Close stuff
inStream.close();
outStream.close();
rbc.close();

推荐答案

使用Long.MAX_VALUE，如果可以的话，请使用Blob的长度.

Use Long.MAX_VALUE, or the length of the Blob if you can get it.

"ReadableByteChannel的长度"通常毫无意义.考虑一个SocketChannel，其对等方永远不会关闭连接.

'Length of a ReadableByteChannel' is meaningless in general. Consider a SocketChannel whose peer never closes the connection.

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