7-RandomAccessFile 随机流

package com.io;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

import org.junit.Test;

/*
 *  RandomAccessFile:支持随机访问
 *    1、即可充当一个输入流，又可充当一个输出流
 *    2、支持从任意位置读写
 */
public class RandomAccessFileTest {
    
    

    @Test
    public void testRandomAccessFile(){
        /*
         * 创建RandomAccessFile对象有两个参数，
         * 一个是file对象，一个是此RandomAccessFile对象对文件读写的权限，有以下四种 
         * 
         * r: 以只读方式打开
         * rw：打开以便读取和写入
         * rwd:打开以便读取和写入；同步文件内容的更新
         * rws:打开以便读取和写入；同步文件内容和元数据的更新

         */
        RandomAccessFile raf_read = null;
        RandomAccessFile raf_write = null;
        try {
            raf_read = new RandomAccessFile(new File("random.txt"), "r");
            raf_write = new RandomAccessFile(new File("random_new.txt"), "rw");

            byte[] b = new byte[20];
            int len;
            while((len = raf_read.read(b)) != -1){
                raf_write.write(b, 0, len);
            };
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                raf_write.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            
            try {
                raf_read.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
    
    @Test
    public void 覆盖(){
        RandomAccessFile raf = null;
        try {
            raf = new RandomAccessFile(new File("random.txt"), "rw");
            raf.seek(3);//把指针移到第3个字节
            raf.write("xy".getBytes());
        }  catch (IOException e) {
            e.printStackTrace();
        }finally{
        try {
            raf.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        }
    }
    
    //单行插入字符
    @Test
    public void 插入字符串(){
        RandomAccessFile raf = null;
        try {
            raf = new RandomAccessFile(new File("random.txt"), "rw");
            raf.seek(3);//把指针移到第3个字节
            String str = raf.readLine();
            System.out.println(raf.getFilePointer());//指针位置
            raf.seek(3);
            raf.write("xy".getBytes());
            raf.write(str.getBytes());
        }  catch (IOException e) {
            e.printStackTrace();
        }finally{
        try {
            raf.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        }
    }
    
    
    
    //多行插入字符
        @Test
        public void 多行插入字符串(){
            RandomAccessFile raf = null;
            try {
                raf = new RandomAccessFile(new File("random_lines.txt"), "rw");
                raf.seek(3);//把指针移到第3个字节
                 byte [] b = new byte[20];
                 int len;
                 StringBuffer sbr = new StringBuffer();
                 while((len = raf.read(b)) != -1){
                     sbr.append(new String(b,0,len));
                 }
                 System.out.println(raf.getFilePointer());
                 raf.seek(3);
                 raf.write("xy".getBytes());
            }  catch (IOException e) {
                e.printStackTrace();
            }finally{
            try {
                raf.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            }
        }
}