Java使用RandomAccessFile类对文件进行读写

RandomAccessFile(String name, String mode)
RandomAccessFile(File file, String mode)

//创建目录
File dir = new File("demo");
if (!dir.exists()) {
  dir.mkdir();
}
//创建文件
File file = new File(dir, "test.dat");
if (!file.exists()) {
  file.createNewFile();
}
//实例化RandomAccessFile对象
RandomAccessFile raf = new RandomAccessFile(file, "rw");
//打开文件时指针位置在最前，即0
System.out.println(raf.getFilePointer());

write(int i)
write(byte[] b)
write(byte[] b, int off, int len)

//write()方法每次只插入一个字节，大于一个字节的则写入后八位，因此写入一个整型数需要写入四次
int num = 28;
raf.write(num >>> 24);
raf.write(num >>> 16);
raf.write(num >>> 8);
raf.write(num);

public final void writeInt(int v) throws IOException {
  write((v >>> 24) & xFF);
  write((v >>> 16) & xFF);
  write((v >>> 8) & xFF);
  write((v >>> 0) & xFF);
  //written += 4;
}

read(int i)
read(byte[] b)
read(byte[] b, int off, int len)

//读取文件，在读取前需要通过seek()方法把文件指针移到最前
raf.seek(0);
for (int i = 0; i*4 < raf.length(); i++) {
  System.out.println(raf.readInt());
}

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

public class MyRandomAccessFile {

  public static void main(String[] args) throws IOException {
    //创建目录
    File dir = new File("demo");
    if (!dir.exists()) {
      dir.mkdir();
    }
    //创建文件
    File file = new File(dir, "test.dat");
    if (!file.exists()) {
      file.createNewFile();
    }
    
    //实例化RandomAccessFile对象
    RandomAccessFile raf = new RandomAccessFile(file, "rw");
    //打开文件时指针位置在最前，即0
    System.out.println(raf.getFilePointer());

    //写入数据
    int[] num = {28, 14, 56, 23, 98};
    for (int i : num) {
      raf.writeInt(i);
    }
    
    //读取文件，在读取前需要通过seek()方法把文件指针移到最前
    raf.seek(0);
    for (int i = 0; i*4 < raf.length(); i++) {
      System.out.println(raf.readInt());
    }
    
    //操作结束后一定要关闭文件
    raf.close();
  }
}