import java.awt.Color;
import java.awt.Insets;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.text.BadLocationException;
import javax.swing.text.Utilities;

public class NumberedTextArea  implements ComponentListener, KeyListener {

    private static final long serialVersionUID = 1L;

    private JTextArea textArea, numberArea;

    private boolean areaLineBreak = true;

    private boolean numberLineBreak = true;

    private String datNam = "test.txt";

    private static final int ROWS = 20, COLS = 60;

    public NumberedTextArea() {
        init();
    }
    
    private void init() {
        textArea = new JTextArea(ROWS, COLS);
        textArea.setMargin(new Insets(0, 10, 0, 10));
        textArea.setLineWrap(areaLineBreak);
        textArea.setWrapStyleWord(areaLineBreak);
        textArea.addComponentListener(this);
        textArea.addKeyListener(this);
        textArea.setText(ladeDatei(datNam));
        
        JScrollPane sp = new JScrollPane();
        sp.setViewportView(textArea);
        sp.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        sp.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);

        numberArea = new JTextArea();
        gibNummern();
        numberArea.setMargin(new Insets(0, 4, 0, 4));
        numberArea.setBackground(new Color(240, 240, 255));
        numberArea.setForeground(new Color(180, 180, 180));
        numberArea.setEditable(false);
        sp.setRowHeaderView(numberArea);
        
        JFrame frame = new JFrame();
        frame.add(sp);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private String ladeDatei(String datName) {

        File file = new File(datName);

        if (!file.canRead() || !file.isFile()) {
            System.err.println("Datei nicht vorhanden oder nicht lesbar!");
            System.exit(0);
        }
        FileReader fr = null;
        int c;
        StringBuffer buff = new StringBuffer();
        try {
            fr = new FileReader(file);
            while ((c = fr.read()) != -1) {
                buff.append((char) c);
            }
            fr.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
        return buff.toString();
    }

    public void gibNummern() {
        StringBuilder sb = new StringBuilder();
        int zeilenZahl = textArea.getLineCount();
        int textLength = textArea.getText().length();

        if (!areaLineBreak & zeilenZahl != 0) {
            for (int i = 0; i < zeilenZahl; i++) {
                sb.append(String.valueOf(i + 1) + "\n");
            }
        }

        try {
            if (numberLineBreak && areaLineBreak) {
                Pattern p = Pattern.compile(System.getProperty("line.separator"));
                sb.append("1\n");
                int n = 1;
                for (int i = 0; i < textLength; i++) {
                    int lineEnd = Utilities.getRowEnd(textArea, i);
                    int lineStart = Utilities.getRowEnd(textArea, i + 1);
                    if (lineEnd < lineStart) {
                        String s = textArea.getText().substring(lineEnd, lineStart);
                        Matcher m = p.matcher(s);
                        boolean result = m.find();
                        if (!result) {
                            sb.append("\n");
                        } else {
                            n++;
                            sb.append(String.valueOf(n) + "\n");
                        }
                    }
                }

            } else if (!numberLineBreak && areaLineBreak) {
                int n = 0;

                for (int i = 0; i < textLength; i++) {
                    int lineEnd = Utilities.getRowEnd(textArea, i);
                    int lineStart = Utilities.getRowEnd(textArea, i + 1);
                    if (lineEnd < lineStart) {
                        n++;
                        sb.append(String.valueOf(n) + "\n");
                    }
                }

                sb.append(String.valueOf(++n) + "\n");
            }
        } catch (BadLocationException e1) {
            e1.printStackTrace();
        }
        numberArea.setText(sb.toString());
    }

    public void componentHidden(ComponentEvent e) {
    }

    public void componentMoved(ComponentEvent e) {
    }

    public void componentResized(ComponentEvent e) {
        gibNummern();
    }

    public void componentShown(ComponentEvent e) {
    }

    public void keyPressed(KeyEvent e) {
    }

    public void keyReleased(KeyEvent e) {
        gibNummern();
    }

    public void keyTyped(KeyEvent e) {
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new NumberedTextArea());
    }
}