MarkdownParse.java

//https://howtodoinjava.com/java/io/java-read-file-to-string-examples/

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;

import javax.script.ScriptContext;

public class MarkdownParse {

    public static ArrayList<String> getLinks(String markdown) {
        ArrayList<String> toReturn = new ArrayList<>();
        // find the next [, then find the ], then find the (, then read link upto next )
        // unsafe url characters: "{", "}", "|", "\", "^", "~", "[", "]", " ", and "`"
        // if one of these characters exists before the close parens, we assume the url is overs
        int currentIndex = 0;
        
        while(currentIndex < markdown.length()) {
            int openBracket = markdown.indexOf("[", currentIndex);
            int closeBracket = markdown.indexOf("]", openBracket);
            int openParen = markdown.indexOf("(", closeBracket);
            int closeParen = markdown.indexOf(")", openParen);
        
            
            if(closeBracket == -1 || openBracket == -1 || closeParen == -1|| openParen == -1)
                break;
            if(openParen - closeBracket == 1) //only add if the openParen and closeBracket are adjacent
            {
                try
                {
                    if (!(markdown.substring(openBracket - 1, openBracket).equals("!"))) //only add it if it's not an image
                    {
                        toReturn.add(markdown.substring(openParen + 1, closeParen));
                    }
                }
                //if open bracket is at index 0, then it's a link and not an image so run as normal.
                catch(IndexOutOfBoundsException e)
                {
                    toReturn.add(markdown.substring(openParen + 1, closeParen));
                }
            }
            currentIndex = closeParen + 1;
        }
        return toReturn;
    }


    public static void main(String[] args) throws IOException {
        Path fileName = Path.of(args[0]);
        System.out.println(Files.readString(fileName));
        String content = Files.readString(fileName);
        ArrayList<String> links = getLinks(content);
        System.out.println(links);
    }
}