JAVA Scan from textfile and display only text between two key words/variables

Question

I need help displaying only text from within a file that begins with lets say the word "Hello" and ends at the word "Bye". I'm able to scan the whole text file and print it, but I need it to only print out a specific range defined by two variables. This is what I have so far, any tips will be appreciated. Thanks! :)

public static void main(String[] args) {
    // TODO code application logic here
    File fileName = new File("hello.txt");
    try {
        Scanner scan = new Scanner(fileName);
        while (scan.hasNextLine()) {
            String line = scan.nextLine();
            System.out.println(line);
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

Answer 1

How big is the file? I unless its large, read the file as a string and cut out the bit you want.

File file = new File("Hello.txt");
FileInputStream fis = new FileInputStream(file);
byte[] bytes = new byte[(int) file.length()];
fis.read(bytes);
fis.close();
String text = new String(bytes, "UTF-8");
System.out.println(text.substring(text.indexOf("START"), text.lastIndexOf("END")));

Using Apache FileUtils

String text = FileUtils.readFileToString("hello.txt");
System.out.println(text.substring(text.indexOf("START"), text.lastIndexOf("END")));

Answer 2

public static void main(String[] args) {
    // TODO code application logic here
    File fileName = new File("hello.txt");
    try {
        Scanner scan = new Scanner(fileName);
        while (scan.hasNextLine()) {
            String line = scan.nextLine();
            System.out.println(line);
            int indexHello = line.lastIndexOf("hello",0);
            int indexBye = line.indexOf("bye". indexHello);
            String newString = line.substring(indexHello, indexBye);


        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

Answer 3

I'm not sure whether you meant that Hello and Bye had to be on the same line or spanned over multiple lines? Try this (modify startToken and endToken to suit):

public static void main(String[] args) {
    // TODO code application logic here
    File fileName = new File("hello.txt");
    try {
        String startToken = "Hello";
        String endToken = "Bye";
        boolean output = false;

        Scanner scan = new Scanner(fileName);
        while (scan.hasNextLine()) {
            String line = scan.nextLine();
            if (!output && line.indexOf(startToken) > -1) {
                output = true;
                line = line.substring(line.indexOf(startToken)+startToken.length());
            } else if (output && line.indexOf(endToken) > -1) {
                output = false;
                System.out.println(line.substring(0, line.indexOf(endToken)));
            }

            if (output) {
                System.out.println(line);
            }
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}

Answer 4

You can use a state variable to store whether you are between a "Hello" / "Bye" pair or not. Change the variable according to what you find in the input. Print text according to the state you are in.

I leave the implementation in Java to you. :-)