How to validate if .txt file format is correct as a part of File processing in Automation framework?

Question

In my Selenium+Java automation framework, I need to open a .txt file or any other extension file and then see if the text is in a particular format. Now, I need to see if all lines are in this format and also, say in line 2, from substring (7,10) is 2000. Now, is there any method in FileUtils API?

I can open the file and assert that it exists. I am not able to validate File content. I need to do this as a part of my Automation project. this is indeed the purpose of my project to validate all file format contents.

Like:

0000000TEst  123  234   TEST22 refreence 0002343
00000002000     2343   23343  TEST22000000000000000000
000000003534   3434    34343  3434 343 343 TEst 0000000 000 000              001

Update in response to answers:

Thanks! this is very helpful, i will use this method to verify all the file formats with regex.

Also, once i validate the format, then i will validate some substrings. Now, i have the expected result of Substring stored in String line2Value = "2000";

if(line1.substring(7,10).equals(line2Value)){

// syso("This is correct....."
}

Now, I have such kind of a file in which some section of records, some regex repeats n number of times.
{1:TES001}{2:TEST002}{3:
:03:192sscE8wre
:04:TESTLIne
:05C:23434/23423
:06:/
:07:343434,434343//3434343434
:89:?This is test line / EXTRA TEXT LINE
-}
My file will have hundreds of these sections, that all start from {1:... and end with -89 }..

how i can check not just 1 section, but all of these groups are in the same format :/

Answer 1

see if the text is in a particular format

For this, you can use regular expressions. Here is a tutorial:

https://www.baeldung.com/regular-expressions-java

(I will try to add the exact regex when we know what format are we looking for)

also, say in line 2, from substring (7,10) is 2000

For this, you can use Substring:

assertThat(myString.substring(7, 10)).equals("2000")