How to read from a .txt file but between two points in the file

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Hello!

I have been trying to figure out how to read from a .txt file. I know how to read a whole file, but I am having difficulties reading between two specific points in a file.
I am also trying to use the scanner class and this is what I have so far:

C#

public void readFiles(String fileString)throws FileNotFoundException{
      
        file = new File(fileString);
        Scanner scanner = null; 
        line=""; 
       

        //access file
        try {
            scanner = new Scanner(file);
        } 
        catch (FileNotFoundException e) {
            System.out.println("File not found.");
        }
         
       
            // if more lines in file, go to next line
           while (scanner.hasNext())
            {
               line = scanner.next();
              
               
               if (scanner.equals("BGSTART")) //tag in the txt to locate position
               {
                   line = scanner.nextLine();
                   System.out.println(line);
                   lb1.append(line); //attaches to a JTextArea.
                   window2.add(lb1);//adds to JPanel
                }
            }

.txt file looks something like this:

BGSTART
//content
BGEND

I am trying to read it between those tow points.
Any suggestions?
Thank You.

Posted 16-Feb-15 3:47am

varoag

Updated 16-Feb-15 4:08am

phil.o

v2

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ZurdoDev 16-Feb-15 10:15am

You can read all lines into an array and then loop through. When you hit BGSTART do what you need to until you hit BGEND.

PIEBALDconsult 16-Feb-15 10:22am

How big is the file? Is it worth reading it all in and using a Regular Expression to select the section you need?

varoag 16-Feb-15 10:26am

there isn't too much content. About 25 lines. But I need to have it in one file and read from it.

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CPallini · Answer 1 · 2015-02-16T05:50:00

try

Java

public void readFile(String fileString) throws IOException
 {

   File file = new File(fileString);
   Scanner scanner = null;
   String line = "";


  //access file
   try
   {
     scanner = new Scanner(file);
   }
   catch (FileNotFoundException e)
   {
     System.out.println("File not found.");
   }


   // if more lines in file, go to next line

   boolean gatheringData = false;

   while (scanner.hasNext())
   {
     line = scanner.next();
     if ( gatheringData )
     {
       if ( line.equals("BGEND") )
         break;

       System.out.println(line); // add this line to JTextArea

     }
     else if ( line.equals("BGSTART") )
     {
       gatheringData = true;
     }
   }
 }

Thomas Daniels · Answer 2 · 2015-02-16T05:06:00

Try this:

Java

public static void readFiles(String fileString)
        throws FileNotFoundException {

    File file = new File(fileString);
    Scanner scanner = null;
    String line = "";

    // access file
    try {
        scanner = new Scanner(file);
    } catch (FileNotFoundException e) {
        System.out.println("File not found.");
        return; // don't continue if the file is not found
    }

    // if more lines in file, go to next line
    Boolean started = false;
    while (scanner.hasNext()) {
        line = scanner.nextLine();

        if (line.equals("BGEND")) {
            started = false;
            // if you also immediately want to go out of the loop,
            // un-comment the following line:
            // break;
        }

        if (started) // tag in the txt to locate position
        {
            System.out.println(line);
            lb1.append(line); //attaches to a JTextArea.
            window2.add(lb1); //adds to JPanel
        }

        if (line.equals("BGSTART")) {
            started = true;
        }
    }
    scanner.close();
}

How does it work?

It goes through the lines.
It the line equals BGEND, it sets started to false.
If started equals true, it performs the actions with the line such as printing it.
If the line equals BGSTART, it sets started to true.

The order of these steps is important, because BGSTART and BGEND don't have to be printed themselves.

Some other changes:

In the catch block, you should return, because if you don't, the method continues without the scanner is created.
The scanner should be closed at the end.

How to read from a .txt file but between two points in the file

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