Question

I need to parse a log file which is in txt format.

I need to match the String and read above and below lines of the matched String.

I need to do something similar to grep -A 30 -B 50 'hello'.

If You have any other suggestions to do it you are welcome.

Answer 1

You may use following code(uses java 5 api java.util.Scanner):

    Scanner scanner = new Scanner(new File("YourFilePath"));
    String prev = null;
    String current;
    while (scanner.hasNextLine())
    {
        current = scanner.nextLine();
        if (current.contains("YourRegEx"))
            break;
        else
            prev = current;
    }
    String next = scanner.nextLine();

You may want to add additional checks for prev being not null and Calling scanner.hasNextLine() before String next = scanner.nextLine()