网络I/o编程模型5 Nio之buffer的操作和常用方法

1.代码

public class RandomBuffer {
    public static void main(String[] args) {
         Random random = new Random();
        IntBuffer buffer = IntBuffer.allocate(5);
        buffer.put(1);
        buffer.put(2);
        buffer.put(3);
        buffer.put(4);
        buffer.put(5);
        buffer.clear();
        while (buffer.hasRemaining()) {
             buffer.put(random.nextInt());
           }
          buffer.flip();
        while (buffer.hasRemaining()) {
                  System.out.println(buffer.get());
         }
    }
}

2.没有执行clear方法前

3.执行clear方法后：

1.代码

package com.ljf.netty.nio;

import java.nio.ByteBuffer;


public class ReadOnlyBuffer {
    public static void main(String[] args) {
        //创建一个buffer
        ByteBuffer buffer=ByteBuffer.allocate(64);
        for(int i=0;i<10;i++){
            buffer.put((byte)i);
        }
        //读取切换，从写切换到读
         buffer.flip();
        //得到一个只读的Buffer
        ByteBuffer readOnlyBuffer=buffer.asReadOnlyBuffer();
        System.out.println("可读:"+readOnlyBuffer.getClass());
        while (readOnlyBuffer.hasRemaining()){
            System.out.println("du:"+readOnlyBuffer.get());
        }
        //这个时候再向里面添加，则报错！！！
        readOnlyBuffer.put((byte)100);
    }
}

2.查看结果

MappedByteBuffer 可让文件直接在内存（堆外内存）修改，操作系统不需要拷贝一次。

1.代码

package com.ljf.netty.nio;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;


public class RandomAccessFileDemo {
    public static void main(String[] args) throws IOException {
        RandomAccessFile   randomAccessFile=new RandomAccessFile("d:/liu.txt","rw");
        //获取对应的通道
        FileChannel channel=randomAccessFile.getChannel();
        
       MappedByteBuffer   mappedByteBuffer=channel.map(FileChannel.MapMode.READ_WRITE,0,10);
       //修改索引0,3 位置上的内容
       mappedByteBuffer.put(0,(byte)'t');
        mappedByteBuffer.put(3,(byte)'9');
        randomAccessFile.close();
        System.out.println("修改成功!!!");
    }
}

2.看效果