FileChannel类的简单用法

清单一：

import java.io.*;

import java.nio.*;

import java.nio.channels.*;

public class GetChannel

{

private static final int BSIZE = 1024;

public static void main(String[] args)throws IOException

{

FileChannel fc = new FileOutputStream ("data.txt").getChannel();

fc.write(ByteBuffer.wrap("some txt".getBytes()));//write() Writes a sequence of bytes to

//this channel from the given buffer

fc.close();

fc = new RandomAccessFile("data.txt","rw").getChannel();

fc.position(fc.size());//abstract FileChannel position(long newPosition)

//Sets this channel's file position.

fc.write(ByteBuffer.wrap("some more".getBytes()));

fc.close();

fc =new FileInputStream("data.txt").getChannel();

ByteBuffer bf = ByteBuffer.allocate(BSIZE);//static ByteBuffer allocate(int capacity)

//Allocates a new byte buffer.

//一旦调用read（）来告知FileChannel向ByteBuffer存储字节，就必须调用缓冲器上的filp（），

//让它做好别人存储字节的准备（是的，他是有点拙劣，但请记住他是很拙劣的，但却适于获取大速度）

//

fc.read(bf);// Reads a sequence of bytes from this channel into the given buffer

bf.flip();

while(bf.hasRemaining())

System.out.print((char)bf.get());

}

}



清单二：

//Copying a file using channels and buffers;

import java.io.*;

import java.nio.*;

import java.nio.channels.*;

public class ChannelCopy

{

private static final int BSIZE = 1024;

public static void main(String [] args)throws IOException

{

if (args.length!=2)

{

System.out.println("argument:sourcefile destfile");

System.exit(1);

}

FileChannel

in = new FileInputStream (args[0]).getChannel(),

out = new FileOutputStream (args[1]).getChannel();

ByteBuffer bb = ByteBuffer.allocate(BSIZE);

while (in.read(bb)!=-1)

{

bb.flip();

out.write(bb);

bb.clear();//prepare for reading;清空缓冲区；

}

}

}


清单三

import java.io.*;

import java.nio.*;

import java.nio.channels.*;

public class TransferTo

{

public static void main(String [] args) throws IOException

{

if(args.length!=2)

{

System.out.println("argument: sourcefile destfile");

System.exit(1);

}

FileChannel

in = new FileInputStream(args[0]).getChannel(),

out = new FileOutputStream(args[1]).getChannel();

//abstract long transferTo(long position, long count, WritableByteChannel target)

// Transfers bytes from this channel's file to the given writable byte channel.

in.transferTo(0,in.size(),out);

//or

//using out

//abstract long transferFrom(ReadableByteChannel src, long position, long count)

// Transfers bytes into this channel's file from the given readable byte channel.

// out.transferFrom(in,0,in.size());

}

}