Swing method akin to HTML5’s canvas.putImageData(arrayOfPixels, 0,0)

BufferedImage is probably the most flexible choice. You can use it as an Icon or override paintComponent() for the full generality of Java2D.

package overflow;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

/** @see http://stackoverflow.com/questions/7298492 */
public class PiRaster extends JPanel {

    private static final int W = 30;
    private static final int H = 30;
    private static List<Integer> pi = new ArrayList<Integer>();
    private final List<Integer> clut = new ArrayList<Integer>();
    private BufferedImage image;

    public PiRaster() {
        this.setPreferredSize(new Dimension(W * 16, H * 10));
        String s = ""
            + "31415926535897932384626433832795028841971693993751"
            + "05820974944592307816406286208998628034825342117067"
            + "98214808651328230664709384460955058223172535940812"
            + "84811174502841027019385211055596446229489549303819"
            + "64428810975665933446128475648233786783165271201909"
            + "14564856692346034861045432664821339360726024914127";
        for (int i = 0; i < s.length(); i++) {
            pi.add(s.charAt(i) - '0');
        }
        for (int i = 0; i < 10; i++) {
            clut.add(Color.getHSBColor(0.6f, i / 10f, 1).getRGB());
        }
        image = new BufferedImage(W, H, BufferedImage.TYPE_INT_ARGB);
        int i = 0;
        for (int row = 0; row < H; row++) {
            for (int col = 0; col < W; col++) {
                image.setRGB(col, row, clut.get(pi.get(i)));
                if (++i == pi.size()) {
                    i = 0;
                }
            }
        }
    }

    private static class ClutPanel extends JPanel {

        private int i;

        public ClutPanel(List<Integer> rgbList) {
            this.setLayout(new GridLayout(1, 0));
            for (Integer rgb : rgbList) {
                JLabel label = new JLabel(String.valueOf(i++), JLabel.CENTER);
                label.setOpaque(true);
                label.setBackground(new Color(rgb));
                this.add(label);
            }
        }
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(image, 0, 0, getWidth(), getHeight(), null);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                PiRaster pr = new PiRaster();
                Icon icon = new ImageIcon(pr.image);
                frame.add(new JLabel(icon), BorderLayout.WEST);
                frame.add(pr, BorderLayout.CENTER);
                frame.add(new ClutPanel(pr.clut), BorderLayout.SOUTH);
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}