Java NIO知识整理

前几天学了下NIO这块，因之前基本没用到过也算是新知识，这篇文章着重分享Channel，内存映射，缓冲区不会做过多介绍，有兴趣可以百度一下找资料看

一   使用通道边读边写的经典写法

以复制图片到同一个目录为例，把wp.jpg复制一份放到d盘下

package com.debug;

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

public class UseChanel01 {

	public static void main(String[] args) throws Exception {
	
        File f1=new File("d:"+File.separator+"wp.jpg");
        File f2=new File("d:"+File.separator+"wp01.jpg");
        FileInputStream in=new FileInputStream(f1);
        FileOutputStream out=new FileOutputStream(f2);
        
        //取得输入输出流的通道
        FileChannel inChanel=in.getChannel();
        FileChannel outChanel=out.getChannel();
        //开辟缓冲
        ByteBuffer buf=ByteBuffer.allocate(1024);
        
        while(inChanel.read(buf)!=-1) {
        	buf.flip();//重设缓冲区
        	outChanel.write(buf);//输出到缓冲区
        	buf.clear();//清空缓冲区
        	
        }
        outChanel.close();
        inChanel.close();
        out.close();
        in.close();
        
        
	}

}

二  NIO2的写法

NIO2之后简化了获取Channel的方法，不需要通过InputStream和OutoutStream获取，代码如下

package com.debug;

import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class UseChannel02 {

	public static void main(String[] args) throws Exception {
		//NIO2 取得channel(不需要通过输入输出流取得)
		FileChannel inChaeenl=FileChannel.open(Paths.get("d:",File.separator,"wp.jpg"), StandardOpenOption.READ);
		FileChannel outChaeenl=FileChannel.open(Paths.get("d:",File.separator,"wp03.jpg"),StandardOpenOption.READ, StandardOpenOption.WRITE,StandardOpenOption.CREATE);

		//使用内存映射的方式'边读边写'
		MappedByteBuffer mapByteInBuffer=inChaeenl.map(MapMode.READ_ONLY, 0, inChaeenl.size());
		MappedByteBuffer  mapByteOutBuffer=outChaeenl.map(MapMode.READ_WRITE, 0, inChaeenl.size());
		
		byte[] dst=new byte[mapByteInBuffer.limit()];
		mapByteInBuffer.get(dst);
		mapByteOutBuffer.put(dst);
		
		outChaeenl.close();
		inChaeenl.close();
		
	}

}

三  除使用内存映射的方式还有其他使用起来更简洁的API

package com.debug;

import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class UseChannel03 {

	public static void main(String[] args) throws Exception {
		
		//NIO2 取得channel
		FileChannel inChaeenl=FileChannel.open(Paths.get("d:",File.separator,"wp.jpg"), StandardOpenOption.READ);
		FileChannel outChaeenl=FileChannel.open(Paths.get("d:",File.separator,"wp04.jpg"),StandardOpenOption.READ, StandardOpenOption.WRITE,StandardOpenOption.CREATE);

		//使用transferFrom或者transferTo进行边读边写（最简洁的方式）
		outChaeenl.transferFrom(inChaeenl, 0, inChaeenl.size());
		
		outChaeenl.close();
		inChaeenl.close();
		
	}

}