JMultilineTextField.java

JMultilineTextField.java

package com.example;

import javax.swing.JTextField;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.AbstractDocument;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import java.awt.Dimension;
import java.util.stream.Stream;

public class JMultilineTextField extends JTextField {
	public JMultilineTextField() {
		setupDocument(getDocument());

		addActionListener(e -> {
			try {
				final int selectionStart = getSelectionStart();
				final int selectionEnd = getSelectionEnd();

				final Document document = getDocument();
				if (selectionStart != selectionEnd) {
					document.remove(selectionStart, selectionEnd - selectionStart);
				}
				document.insertString(selectionStart, "\n", null);
			} catch (final BadLocationException ble) {
				ble.printStackTrace();
			}
		});
	}

	@Override
	public void setDocument(final Document doc) {
		setupDocument(doc);

		super.setDocument(doc);
	}

	private void setupDocument(final Document doc) {
		doc.putProperty("filterNewlines", false);
		installDocumentListenerIfNecessary(doc);
	}

	private void installDocumentListenerIfNecessary(final Document doc) {
		final DocumentListener documentListeners[] = ((AbstractDocument) doc).getListeners(DocumentListener.class);
		if (Stream.of(documentListeners).noneMatch(documentListener -> documentListener instanceof RowCountChangeListener)) {
			doc.addDocumentListener(new RowCountChangeListener());
		}
	}

	private final class RowCountChangeListener implements DocumentListener {
		@Override
		public void insertUpdate(final DocumentEvent e) {
			revalidateParentIfNecessary();
		}

		@Override
		public void removeUpdate(final DocumentEvent e) {
			revalidateParentIfNecessary();
		}

		@Override
		public void changedUpdate(final DocumentEvent e) {
			revalidateParentIfNecessary();
		}

		private void revalidateParentIfNecessary() {
			final JMultilineTextField textField = JMultilineTextField.this;

			final Dimension currentSize = textField.getSize();
			final Dimension preferredSize = textField.getPreferredSize();

			/*
			 * Grow/shrink vertically as necessary.
			 */
			if (currentSize.height != preferredSize.height) {
				textField.getParent().revalidate();
			}
		}
	}
}