Java Swing: Rainbow border for a JComponent

问题

I'm currently designing a title screen for a game. When designing the logo I decided to go with a rainbow border around the edges:

I figured after this I would like to implement the rest of my components on the title screen with a similar rainbow border (Specifically JButtons). While looking for ways to do this I came across the AbstractBorder class. My question is, is this even possible to do and if it is, What is the most effective way to use the Abstract border class to generate a rainbow border based on the size of the component?

回答1:

The basic approach is to use a LinearGradientPaint to paint the rainbow effect, for example...

public class RainbowBorder extends AbstractBorder {

    @Override
    public Insets getBorderInsets(Component c, Insets insets) {
        insets.bottom = insets.top = insets.left = insets.right = 1;
        return insets;
    }

    @Override
    public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
        Graphics2D g2d = (Graphics2D) g.create();
        LinearGradientPaint lpg = new LinearGradientPaint(
            new Point(x, y),
            new Point(x, y + height),
            new float[]{0.0f, 0.25f, 0.5f, 0.75f, 1.0f},
            new Color[]{Color.YELLOW, Color.GREEN, Color.CYAN, Color.BLUE, Color.MAGENTA});
        g2d.setPaint(lpg);
        g2d.draw(new Rectangle2D.Double(x, y, width - 1, height - 1));
        g2d.dispose();
    }

}

And as a proof of concept

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.LinearGradientPaint;
import java.awt.Point;
import java.awt.geom.Rectangle2D;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.AbstractBorder;
import javax.swing.border.CompoundBorder;
import javax.swing.border.EmptyBorder;

public class TextOutline {

    public static void main(String[] args) {
        new TextOutline();
    }

    public TextOutline() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class RainbowBorder extends AbstractBorder {

        @Override
        public Insets getBorderInsets(Component c) {
            return super.getBorderInsets(c); //To change body of generated methods, choose Tools | Templates.
        }

        @Override
        public Insets getBorderInsets(Component c, Insets insets) {
            insets.bottom = insets.top = insets.left = insets.right = 1;
            return insets;
        }

        @Override
        public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
            Graphics2D g2d = (Graphics2D) g.create();
            LinearGradientPaint lpg = new LinearGradientPaint(
                new Point(x, y),
                new Point(x, y + height),
                new float[]{0.0f, 0.25f, 0.5f, 0.75f, 1.0f},
                new Color[]{Color.YELLOW,    Color.GREEN, Color.CYAN, Color.BLUE, Color.MAGENTA});
            g2d.setPaint(lpg);
            g2d.draw(new Rectangle2D.Double(x, y, width - 1, height - 1));
            g2d.dispose();
        }

    }

    class TestPane extends JPanel {

        public TestPane() {
            setLayout(new BorderLayout());
            setBorder(
                new CompoundBorder(
                    new EmptyBorder(10, 10, 10, 10),
                    new CompoundBorder(
                        new RainbowBorder(), 
                        new EmptyBorder(10, 10, 10, 10))
            ));
            add(new JLabel("Rainbow and unicorns"));
        }
    }
}

来源：https://stackoverflow.com/questions/44349038/java-swing-rainbow-border-for-a-jcomponent