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Java NIO Channel to Channel Transfers

时间:2014-11-20 09:04:49      阅读:450      评论:0      收藏:0      [点我收藏+]

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Java Nio 

1Java NIO Tutorial
2Java NIO Overview
3Java NIO Channel
4Java NIO Buffer
5Java NIO Scatter / Gather
6Java NIO Channel to Channel Transfers
7Java NIO Selector
8Java NIO FileChannel
9Java NIO SocketChannel
10Java NIO ServerSocketChannel
11Java NIO DatagramChannel
12Java NIO Pipe
13Java NIO vs. IO

Java NIO Channel to Channel Transfers

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By Jakob Jenkov
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In Java NIO you can transfer data directly from one channel to another, if one of the channels is a FileChannel. TheFileChannel class has a transferTo() and a transferFrom() method which does this for you.

transferFrom()

The FileChannel.transferFrom() method transfers data from a source channel into the FileChannel. Here is a simple example:

RandomAccessFile fromFile = new RandomAccessFile("fromFile.txt", "rw");
FileChannel      fromChannel = fromFile.getChannel();

RandomAccessFile toFile = new RandomAccessFile("toFile.txt", "rw");
FileChannel      toChannel = toFile.getChannel();

long position = 0;
long count    = fromChannel.size();

toChannel.transferFrom(fromChannel, position, count);

The parameters position and count, tell where in the destination file to start writing (position), and how many bytes to transfer maximally (count). If the source channel has fewer than count bytes, less is transfered.

Additionally, some SocketChannel implementations may transfer only the data the SocketChannel has ready in its internal buffer here and now - even if the SocketChannel may later have more data available. Thus, it may not transfer the entire data requested (count) from the SocketChannel into FileChannel.

transferTo()

The transferTo() method transfer from a FileChannel into some other channel. Here is a simple example:

RandomAccessFile fromFile = new RandomAccessFile("fromFile.txt", "rw");
FileChannel      fromChannel = fromFile.getChannel();

RandomAccessFile toFile = new RandomAccessFile("toFile.txt", "rw");
FileChannel      toChannel = toFile.getChannel();

long position = 0;
long count    = fromChannel.size();

fromChannel.transferTo(position, count, toChannel);

Notice how similar the example is to the previous. The only real difference is the which FileChannel object the method is called on. The rest is the same.

The issue with SocketChannel is also present with the transferTo() method. The SocketChannelimplementation may only transfer bytes from the FileChannel until the send buffer is full, and then stop.







Java NIO Channel to Channel Transfers

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原文地址:http://blog.csdn.net/opengl_es/article/details/41307695

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