I'm looking for a proper regex cheatsheet.

Question about the task

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What is the regex for: somewhere in the string find "wordA" followed by anything till "wordB"? I'm able to get the tags but due to the nested tags it adds too many tags. I think the solution would be in a proper match of the opening and closing tag. I can't find a website with properly described regex rules that is not either overwhelming or very obtuse. Please help me find a good one. Would really appreciate it!!

Read from the console the name of a file containing HTML.

Example:
Info about Leela Leela Turanga
Supergirl

The main method's first parameter is a tag name. For example, "span".
Display all tags that match the specified tag.
The order should match their order in the file, each tag on a new line.
The number of spaces, newline characters (\n), or carriage returns (\r) does not affect the result.
The file does not have a CDATA tag. Each opening tag has a separate closing tag, and there are no self-closing tags.
Tags may have nested tags.

Example output:
Leela Turanga Leela Turanga Super girl

Tag templates:
<tag>text1</tag> <tag text2>text1</tag> <tag text2>text1</tag>

text1 and text2 can be empty

Requirements:

The program must read the file name from the console (use BufferedReader).
The BufferedReader used for reading input from the console must be closed after use.
The program must read the file's contents (use FileReader).
The file input stream (FileReader) must be closed.
The program must write to the console all the tags that match the tag specified by the argument passed to the main method.

package com.codegym.task.task19.task1918; /* Introducing tags /Users/lilianetop/Desktop/taak1917.txt */ import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.regex.Matcher; import java.util.regex.Pattern; public class Solution { public static void main(String[] args) throws IOException { //1. The program must read the file name from the console (use BufferedReader). //2. try-with resources closes the stream automatically String fileName; try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) { fileName = reader.readLine(); } //3. The program must read the file's contents (use FileReader). //4. The file input stream (FileReader) must be closed. (autoclosable) //5. The program must write to the console all the tags that match the tag specified by the argument passed to the main method. try (BufferedReader reader2 = new BufferedReader(new FileReader(fileName))) { String line; //problem is that the closing tag is on the next line so it is perceived as another String so I have to use a Stringbuilder StringBuilder stringBuilder = new StringBuilder(); while (reader2.ready()) { line = reader2.readLine(); stringBuilder.append(line); } //if args[0] = "span"; openingTag = "; String result = stringBuilder.toString(); Pattern pattern1 = Pattern.compile(openingTag); Pattern pattern2 = Pattern.compile(closingTag); Matcher matcher1 = pattern1.matcher(result); Matcher matcher2 = pattern2.matcher(result); while(matcher1.find() && matcher2.find()){ System.out.println(result.substring(matcher1.start(), matcher2.end())); } /*if (result.contains(openingTag)) { //it only finds 1 pair how to get them all? System.out.println(result.substring(result.indexOf(openingTag), result.indexOf(closingTag) + closingTag.length())); }*/ } } }

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Nouser

Level 36 , Germany

11 January 2021, 14:09

regex isn't your friend here... just think about a regex for span tags that are nested 4 levels deep or 8. Where do you want to set a limit? With a loop and using the String class you won't have to.

Liliane Top Backend Developer at Procura

11 January 2021, 14:27

Thanks I went down the rabbit hole haha. I do not know how to deal with the nested tags. I tried using a TreeSet and skipping over if the equals in and counting sequences but to no avail. These past 3 task are really hard. I have no idea how to solve this one. Shame to admit defeat.

Nouser

Level 36 , Germany

11 January 2021, 15:04

My first solution for this task was code hell, the second one looks far cleaner... but I have forgotten how long I needed for that. Probably to long :) Here I read the content of the file into a one line string (used readLine, hence the linebreaks already were gone, therefore I added a space for each one - otherwise tags may grow together). You also just could use read() and keep everything as is. Then I started a loop over the string from pos 0 to string.length() - endTag.length() Then I looked for the first occurence of the starting tag (save index) and started a new loop (from saved index + start tag length to end - end tag length). Now looking for start tags and end tags. found a start tag: counter++ found an end tag: is counter 0, yes -> substring saved index to current index, no -> counter-- when you leave the inner loop, the outer one continues and finds the nested inner tags. pretty easy once you have a rough idea;) And all these task now are hard as hell. I have to admit that I admire your will and how fast you proceed. That last solution of the file comparison task was pretty neat, too. Unfortunately it needed some extra checks.

Liliane Top Backend Developer at Procura

11 January 2021, 17:52

I'll give it another go tomorrow as I tried to do the counting but it became so complicate especially if you have more than one nested <tag>. I would like otherwise to try it with recursive or something. But I also struggle with regex. If I want to use also in other task to find if a String has a digits I also go down a rabbit hole as I don't understand the regex when it goes beyond the basics. Thanks again for helping my, I really appreciate it!

Nouser

Level 36 , Germany

15 January 2021, 08:56

solution

cause I just stumbled over that https://docs.oracle.com/javase/tutorial/essential/regex/index.html

Liliane Top Backend Developer at Procura

15 January 2021, 11:36

I'm going🤬 I'm still trying to figure out this task. I can't stand it that I'm too stupid to figure this one out. It have all the tags including the nested nested tags but somehow I can't get the subString of a tag to be added to the arraylist. I'm trying to remove the additional closingtags on certain lines but it is not working. 🤯

Liliane Top Backend Developer at Procura

15 January 2021, 11:47

And I finally fixed it by myself after more than a week? I just didn't know that to remove part of the Stringbuilder you hav eto use delete() I didn't realise that using substring didn't do anything.

while (closingX > openingX) {
                        closingX--;
                        tag.delete(tag.lastIndexOf(closingTag), tag.length());
                    }

Liliane Top Backend Developer at Procura

16 January 2021, 08:39

Thanks you again I'm practicing with regex and your link is really exactly what I was looking for! 🙏🙏🙏

Nouser

Level 36 , Germany

16 January 2021, 10:33

The entire oracle java tutorials section is worth a look and may help you with hard tasks :)