NIO学习笔记六：channel 之前数据传输及scatter/gather

在Java NIO中，如果两个通道中有一个是FileChannel，那你可以直接将数据从一个channel传输到另外一个channel。

FileChannel的transferFrom()方法可以将数据从源通道传输到FileChannel中
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(position, count, fromChannel);
方法的输入参数position表示从position处开始向目标文件写入数据，count表示最多传输的字节数。
transferTo()方法将数据从FileChannel传输到其他的channel中
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);

Java NIO开始支持scatter/gather
分散（scatter）指在读操作时将读取的数据写入多个buffer中

ByteBuffer header = ByteBuffer.allocate(128);
ByteBuffer body = ByteBuffer.allocate(1024);
ByteBuffer[] bufferArray = { header, body };
channel.read(bufferArray);

聚集（gather）指在写操作时将多个buffer的数据写入同一个Channel

ByteBuffer header = ByteBuffer.allocate(128);
ByteBuffer body = ByteBuffer.allocate(1024);
ByteBuffer[] bufferArray = { header, body };
channel.write(bufferArray);