使用RandomAccessFile java读取直到文件中的特定索引

Question

I was trying to read from a file between two specific indices using the RandomAccessFile.

I know I can jump to an index with the seek() function, but i couldn't find the answer how to read then text out of the file until a specific index.

For example i have a huge file and i want to read text from index 100 to index 500, i would start like this:

public String get_text(){
   raf.seek(100) //raf= my RandomAccessFile
   String txt=raf.read(500) //read until index 500 which i don't know how to do
   return txt;
}

Please help me :)

Answer 1

This is how I solved my Problem:

try {
    int index = 100;
    raf.seek(index); //index = 100
    int counter = 0;
    int length = 400;
    while (counter < length) { //want to read the characters 400 times
       char c = (char) raf.read();
       if (!(c == '\n')) {   //don't append the newline character to my result
           sb.append(c);    //sb is a StringBuilder
           counter++;
       }
    }
} catch (IOException e) {
    e.printStackTrace();
}

I saw also another solution, where readFully() was used with a bytes array, that also worked well.

try {
    raf.seek(index);
    byte[] bytes = raf.readFully(new byte[(int) length]); //length of the charactersequence to be read
    String str = bytes.toString();
} catch (IOException e){
    e.printStackTrace();
}

In this solution the length of the bytes array has to be considered within the newline character, so you have to calculate that considering the line length. ->Start in file with line breaks and end index in file with line breaks. length = endInFile-startInFile +1;