Classe com métodos úteis de tratamentos de imagens. Pegar imagens, gravar, redimencionar / comprimir. Ela utiliza a FileUtils.java também encontrada neste gist

ImageUtils.java

package br.com.helpdev;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.stream.ImageOutputStream;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.*;

public class ImageUtils {

    public static BufferedImage resizeImage(BufferedImage bufferedImage, int width, int height) {
        int type = bufferedImage.getType() == 0 ? BufferedImage.TYPE_INT_ARGB : bufferedImage.getType();

        BufferedImage resizedImage = new BufferedImage(width, height, type);
        Graphics2D g = resizedImage.createGraphics();
        g.drawImage(bufferedImage, 0, 0, width, height, null);
        g.dispose();

        return resizedImage;
    }

    public static byte[] compressImage(BufferedImage bufferedImage, int quality) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        compressImage(bufferedImage, baos, quality);
        return baos.toByteArray();
    }

    public static void compressImage(BufferedImage bufferedImage, File outfile, int quality) throws IOException {
        compressImage(bufferedImage, new FileOutputStream(outfile), quality);
    }


    public static void compressImage(BufferedImage bufferedImage, OutputStream output, int quality) throws IOException {
        if (quality <= 0 || quality > 100) {
            throw new IllegalArgumentException("quality not in 1-100");
        }
        ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();
        try {
            ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
            jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
            jpgWriteParam.setCompressionQuality(quality * 0.01f);
            try (ImageOutputStream ios = ImageIO.createImageOutputStream(output)) {
                jpgWriter.setOutput(ios);
                IIOImage outputImage = new IIOImage(bufferedImage, null, null);
                jpgWriter.write(null, outputImage, jpgWriteParam);
            }
        } finally {
            jpgWriter.dispose();
        }
    }

}