Java RandomAccessFile

1 什么是Java RandomAccessFile

Java RandomAccessFile类是用于读取和写入随机访问文件。随机访问文件的行为类似于大字节数组。有一个指向该数组的游标，称为文件指针，通过移动游标我们可以执行读写操作。如果在读取所需的字节数之前到达文件末尾，则抛出EOFException异常，它是IOException异常的一种。

2 Java RandomAccessFile的构造方法

3 Java RandomAccessFile的方法

4 Java RandomAccessFile的例子

package cn.xnip;

/**
 * 小牛知识库网： https://www.xnip.cn
 */
/**
 *  Java RandomAccessFile的例子
 */
import java.io.IOException;
import java.io.RandomAccessFile;

public class Demo {

    static final String FILEPATH ="file.txt";
    public static void main(String[] args) {
        try {
            System.out.println(new String(readFromFile(FILEPATH, 0, 18)));
            writeToFile(FILEPATH, "I love my country and my people", 31);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    private static byte[] readFromFile(String filePath, int position, int size)
            throws IOException {
        RandomAccessFile file = new RandomAccessFile(filePath, "r");
        file.seek(position);
        byte[] bytes = new byte[size];
        file.read(bytes);
        file.close();
        return bytes;
    }
    private static void writeToFile(String filePath, String data, int position)
            throws IOException {
        RandomAccessFile file = new RandomAccessFile(filePath, "rw");
        file.seek(position);
        file.write(data.getBytes());
        file.close();
    }
}

file.txt的原本内容为：

This class is used for reading and writing to random access file.

执行以上程序后，控制台输出结果为：

This class is used

file.txt的内容改为：

This class is used for reading I love my country and my peoplele.