write string in file if not exist java

Question

i try to write String to file only if String not exist, this is my code

File rule_file = new File("test_rules.rules");
Scanner scanner = new Scanner(rule_file);
PrintWriter writer = new PrintWriter(new FileWriter(rule_file,true));

        while (scanner.hasNextLine()) 
        {
            String lineFromFile = scanner.nextLine();
            if(!rule_write.equals(lineFromFile))
            {
               if(unique.get(nilai_besar).getCount()>10)
               {
                        writer.write(rule_write);
                        writer.close();
                        break;
               }
            }
        }

but, the program keep write String to file even the String already exist in file. Please help, thanks...

Answer 1

You could be writing the extra line after checking just one line of the file.

I suggest you read the file to the end, without attempting to write to it, until you know the line does appear anywhere in the file.

ie I would use a PrintWriter.println() and I would move all the code for writing to after the search loop.

Answer 2

For every line that is not equal you (potentially) try to write to the file.

What you want is to write to the file if all lines are not equal:

    boolean found = false;
    while (scanner.hasNextLine()) 
    {
        String lineFromFile = scanner.nextLine();
        if (rule_write.equals(lineFromFile))
        {
           found = true;
           break;
        }
    }

    if (!found) {
        // append rule_write to the file
        ...
    }

Answer 3

Go with indexOf() or contains() instead of equals() and equalsIgnoreCase(),

I am sure that the line you read may contain

• Empty spaces (before or after)
• Next line problem may occur

If you use indexOf() or contains() , it will check ,whether the line have the string ( rule_write )

Make sure the the values are coming in while()