FileChannel的简单使用

FileChannel主要用来进行对本地文件进行IO操做
1.public int read(ByteBuffer dst):从通道读取数据并放到缓存区中
2.public int write(ByteBuffer src):把缓冲区的数据写到通道中
3.public long transferFrom(ReadableByteChannel src,long position,long count):从目标通道中复制数据到当前通道
4.public long transferTo(long position,long count,WritableByteChannel target):把数据从当前通道复制给目标通道

本地文件写数据

import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class NIOFileChannel01 {

    public static void main(String[] args) throws Exception {
        String s = "test";
        FileOutputStream fileOutputStream = new FileOutputStream("/Users/liaowh/Desktop/test.txt");
        FileChannel fileChannel = fileOutputStream.getChannel();
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        byteBuffer.put(s.getBytes());
        byteBuffer.flip();
        fileChannel.write(byteBuffer);
        fileOutputStream.close();
    }
}

本地文件读数据

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class NIOFileChannel02 {

    public static void main(String[] args) throws Exception {

        File file = new File("/Users/liaowh/Desktop/test.txt");
        FileInputStream fileInputStream = new FileInputStream(file);
        FileChannel fileChannel = fileInputStream.getChannel();
        ByteBuffer byteBuffer = ByteBuffer.allocate((int) file.length());
        fileChannel.read(byteBuffer);
        System.out.println(new String(byteBuffer.array()));
        fileInputStream.close();

    }
}

使用一个Buffer完成文件拷贝

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class NIOFileChannel03 {

    public static void main(String[] args) throws Exception {

        FileInputStream fileInputStream = new FileInputStream("/Users/liaowh/Desktop/test.txt");
        FileChannel fileChannel01 = fileInputStream.getChannel();

        FileOutputStream fileOutputStream = new FileOutputStream("/Users/liaowh/Desktop/test2.txt");
        FileChannel fileChannel02 = fileOutputStream.getChannel();

        ByteBuffer byteBuffer = ByteBuffer.allocate(512);

        while(true){
            byteBuffer.clear();
            int read = fileChannel01.read(byteBuffer);
            if(read == -1){
                break;
            }
            byteBuffer.flip();
            fileChannel02.write(byteBuffer);
        }
        fileInputStream.close();  
        fileOutputStream.close();
    }
}

使用transferFrom()完成文件拷贝

import java.io.FileInputStream;  
import java.io.FileOutputStream;  
import java.nio.channels.FileChannel;  
  
public class NIOFileChannel04 {  
  
    public static void main(String[] args) throws Exception {  
    
  FileInputStream fileInputStream = new FileInputStream("/Users/liaowh/Desktop/test.txt");  
  FileOutputStream fileOutputStream = new FileOutputStream("/Users/liaowh/Desktop/dest.txt");  
  
  FileChannel source = fileInputStream.getChannel();  
  FileChannel dest = fileOutputStream.getChannel();  
  
  dest.transferFrom(source,0,source.size());  
  source.close();  
  dest.close();  
  fileInputStream.close();  
  fileOutputStream.close();  
  
  }  
}