Explanation of data transmission methods between channels in JAVA

In Java NIO, if one of the two channels is a FileChannel, then you can directly transfer data from one channel (Translator's Note: channel is often translated as channel in Chinese) to another channel.

transferFrom(): Passive reception

The transferFrom() method of FileChannel can transfer data from the source channel to the FileChannel (Translator's Note: This method is in the JDK documentation is interpreted as transferring bytes from a given readable byte channel into a file on this channel). The input parameter position of the

method indicates starting from position to write data to the target file, and count indicates the maximum number of bytes transferred. If the source channel has less than count bytes of remaining space, the number of bytes transferred is less than the number of bytes requested.
Also note that in the implementation of SoketChannel, SocketChannel will only transmit the data prepared at this moment (which may be less than count bytes). Therefore, the SocketChannel may not transfer all of the requested data (count bytes) into the FileChannel.

transferTo(): ​​Actively send the

transferTo() method to transfer data from FileChannel to other channels. The following is a simple example:

Except that the FileChannel object calling the method is different, everything else is the same.
The problems mentioned above about SocketChannel also exist in the transferTo() method. SocketChannel will continue to transmit data until the target buffer is filled.

Example:

@Testpublic void test2() {
        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();//从from 读到 本通道；注意socketfrom只会发送已经准备好的，不会发送count个        toChannel.transferFrom(fromChannel,position, count);//将本通道 写到 to；注意sockedfrom会一直发送，直到to被填满        fromChannel.transferTo(position, count, toChannel);
    }

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