随机存取文件流

1、随机存取文件流基本使用

package demo02;

import org.junit.Test;

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

/**
 * @description: demo13
 * @author: liuyang
 * @create: 2021-09-07 17:21
 */
public class Demo13 {
    /**
     * RandomAccessFile:
     * 随机读取文件流，既可以做输入流也能做输出流。
     * 构造器第二个参数mode:
     * r:只能读取
     * rw:读取和写入
     * rwd：读取和写入且实时同步文件内容的更新到磁盘
     * rws：读取和写入且实时同步文件内容和元数据的更新到磁盘
     */
    @Test
    public void test1() {
        RandomAccessFile randomAccessFile1 = null;
        RandomAccessFile randomAccessFile2 = null;
        try {
            randomAccessFile1 = new RandomAccessFile("杨幂.jpg", "r");
            randomAccessFile2 = new RandomAccessFile("杨幂3.jpg", "rw");
            byte[] buff = new byte[1024];
            int len = 0;
            while ((len = randomAccessFile1.read(buff)) != -1) {
                randomAccessFile2.write(buff, 0, len);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (randomAccessFile1 != null) {
                    randomAccessFile1.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (randomAccessFile2 != null) {
                    randomAccessFile2.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

    /**
     * 文件不存在时会自动创建，
     * 文件存在时会对文件的内容从头开始覆盖，而不是对文件进行覆盖
     */
    @Test
    public void test2() {
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile("text8.txt", "rw");
            randomAccessFile.write("abcdefghijklmn".getBytes("UTF-8"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (randomAccessFile != null) {
                    randomAccessFile.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 指定文件写入指针位置，位置从0开始,
     * 若该位置有内容则会对内容进行覆盖
     */
    @Test
    public void test3() {
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile("text8.txt", "rw");
            randomAccessFile.seek(3);
            randomAccessFile.write("DEF".getBytes("UTF-8"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (randomAccessFile != null) {
                    randomAccessFile.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 实现内容插入效果
     */
    @Test
    public void test4() {
        RandomAccessFile raf1 = null;
        RandomAccessFile raf2 = null;
        try {
            File file = new File("text8.txt");
            raf1 = new RandomAccessFile(file, "r");
            raf2 = new RandomAccessFile(file, "rw");
            // 先将指针移动到3的位置，读取包含此位置后面的所有内容
            raf1.seek(3);
            byte[] buff = new byte[1024];
            int len = 0;
            // 暂存读取到的内容
            StringBuilder sb = new StringBuilder();
            while ((len = raf1.read(buff)) != -1) {
                sb.append(new String(buff, 0, len));
            }
            // 将指针重新回到3的位置写入需插入的内容
            raf2.seek(3);
            raf2.write("xyz".getBytes("UTF-8"));
            raf2.write(sb.toString().getBytes("UTF-8"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (raf1 != null) {
                    raf1.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (raf2 != null) {
                    raf2.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 实现内容插入效果
     * 对test4方法进行改造只需要一个rw模式的RandomAccessFile实例即可
     */
    @Test
    public void test5() {
        RandomAccessFile raf1 = null;
        try {
            File file = new File("text8.txt");
            raf1 = new RandomAccessFile(file, "rw");
            // 先将指针移动到3的位置，读取包含此位置后面的所有内容
            raf1.seek(3);
            byte[] buff = new byte[1024];
            int len = 0;
            // 暂存读取到的内容
            StringBuilder sb = new StringBuilder();
            while ((len = raf1.read(buff)) != -1) {
                sb.append(new String(buff, 0, len));
            }
            // 将指针重新回到3的位置写入需插入的内容
            raf1.seek(3);
            raf1.write("xyz".getBytes("UTF-8"));
            raf1.write(sb.toString().getBytes("UTF-8"));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (raf1 != null) {
                    raf1.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}