Java的RandomAccessFile随机文件读写的简单使用

我就是我 2022-07-16 07:49 126阅读 0赞

import java.io.*;
    
    /**
     * Created by cuboo on 2016/10/10.
     */
    public class io {
        public static void main(String agrs[]){
            //写入数据
            File file = new File("test.txt");
            if (!file.exists()) {
                try {
                    file.createNewFile();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            new writeFile(file,6,50,"hello").start();
            new writeFile(file,1,50,"world").start();
            new writeFile(file,2,50,"this").start();
            new writeFile(file,3,50,"is - - - - - -").start();
            new writeFile(file,4,50,"block").start();
    
            //读取数据
            try {
                RandomAccessFile ra = new RandomAccessFile(file,"r");
                ra.seek(100);
                byte bys[] = new byte[10];
                ra.read(bys);
    //            System.out.println(ra.readLine());
                System.out.println(new String(bys));
    
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    }
    
    class writeFile extends Thread {
        File in;
        int block;  //块下标
        int length; //每个块的长度
        String text;
        writeFile(File in,int block,int length,String text){
            this.in = in;
            this.block = block;
            this.length = length;
            this.text = text;
        }
    
        @Override
        public void run() {
            try {
                RandomAccessFile ra = new RandomAccessFile(in,"rw");
                /*
                *  file in 的内容
                *  block 1          block  2            block  3
                * |...................|.....................|
                * |.......length......|........length.......|
                 */
                ra.seek((block-1)*length);//指向block
                ra.writeBytes(text+block);
                ra.writeBytes("\n");
                ra.close();
    
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }