Question

I only want to discuss about this in java/linux context.

RandomAccessFile rand = new RandomAccessFile("test.log", "r");

VS

File file = new File("test.log");

After the creation, we start reading the file to the end.

1. In java.io.File case, it will throw IOException when reading the file if you mv or delete the physical file prior to the file reading.

   public void readIOFile() throws IOException, InterruptedException {
       File file = new File("/tmp/test.log");
       System.out.print("file created"); // convert byte into char
       Thread.sleep(5000);
       while (true) {
           char[] buffer = new char[1024];
           FileReader fr = new FileReader(file);
           fr.read(buffer);
           System.out.println(buffer);
       }
   }
   

2. But in RandomFileAccess case, if you mv or delete the physical file prior to the file reading, it will finish reading the file without errors/exceptions.

   public void readRAF() throws IOException, InterruptedException {
       File file = new File("/tmp/test.log");
       RandomAccessFile rand = new RandomAccessFile(file, "rw");
       System.out.println("file created"); // convert byte into char
       while (true) {
           System.out.println(file.lastModified());
           System.out.println(file.length());
           Thread.sleep(5000);
           System.out.println("finish sleeping");
           int i = (int) rand.length();
           rand.seek(0); // Seek to start point of file
           for (int ct = 0; ct < i; ct++) {
               byte b = rand.readByte(); // read byte from the file
               System.out.print((char) b); // convert byte into char
       }
   }
   

   }

Can anyone explain to me why ? Is there anything to do with file’s inode?

Answer 1

The OS based file system services such as creating folders, files, verifying the permissions, changing file names etc., are provided by the java.io.File class.

The java.io.RandomAccessFile class provides random access to the records that are stored in a data file. Using this class, reading and writing , manipulations to the data can be done. One more flexibility is that it can read and write primitive data types, which helps in structured approach in handling data files.

Unlike the input and output stream classes in java.io, RandomAccessFile is used for both reading and writing files. RandomAccessFile does not inherit from InputStream or OutputStream. It implements the DataInput and DataOutput interfaces.