RadomAccessFile_java读写文件时如…

如果用 流读取文件FileInputStream，FileReader 只能顺序读取。读一个字符指针移动一个位置

如果用 RadomAccessFile，可以用 seek 指定移动到文件的某个位置。
位置定位以字符为单元

要定位到某行，试试 java.io.LineNumberReader 和 java.io.LineNumberInputStream

例子： RadomAccessFile

package org.kodejava.example.io;

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

public class RandomAccessFileExample {

    public static void main(String[] args) {
        try {
            //
            // Create a new instance of RandomAccessFile class. We'll do a "r"
            // read and "w" write operation to the file. If you want to do a write
            // operation you must also allow read opeartion to the RandomAccessFile
            // instance.
            //
            RandomAccessFile raf = new RandomAccessFile("books.dat", "rw");

            //
            // Let's write some book's title to the end of the file
            //
            String books[] = new String[5];
            books[0] = "Professional JSP";
            books[1] = "The Java Application Programming Interface";
            books[2] = "Java Security";
            books[3] = "Java Security Handbook";
            books[4] = "Hacking Exposed J2EE & Java";

            for (int i = 0; i < books.length; i++) {
                raf.writeUTF(books[i]);
            }

            //
            // Write another data at the end of the file.
            //
            raf.seek(raf.length());
            raf.writeUTF("Servlet & JSP Programming");

            //
            // Move the file pointer to the beginning of the file
            //
            raf.seek(0);

            //
            // While the file pointer is less than the file length, read the
            // next strings of data file from the current position of the
            // file pointer.
            //
            while (raf.getFilePointer() < raf.length()) {
                System.out.println(raf.readUTF());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}