I’m working on a photo gallery application running on Java 6 using Tomcat 6, JQuery for the client side, and images and xml generated from Picasa. I needed several sizes of images for thumbnails and animations and I wasn’t about to create multiple image sizes with Fireworks (I’m a lazy developer). Doing what every lazy developer does, I search Google for an image resize solution that would run on the application server and give me the sizes that I needed and take the manual work out of the equation. I found several PHP examples and disjointed Java examples, but no complete solutions. So, unfortunately I had to do some work to put something together.

Down to brass tax, here’s the image resizer servlet code: (copy paste, use as you please)

package com.photo.gallery;

import java.awt.AlphaComposite;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ImageResizer extends HttpServlet {
	/**
	 * Servlet resizes an image located in a directory in a web project ex.
	 * /image?root=/albums&file=/thumbs/imagename.jpg&width=270&height=100 ex.
	 * /image?file=/thumbs/imagename.jpg&width=270 (default root, calculated
	 * height)
	 */
	private static final long serialVersionUID = -8285774993751841288L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) {
		// Optional: Only supports output of jpg and png, defaults to png if not
		// specified
		String imageOutput = getParam(request, "output", "png");
		// Optional: Folder in web app where images are located, defaults to
		// albums if not specified
		String imageRoot = getParam(request, "root", "/albums");
		// Required: Path from root to image, including filename
		String imageFile = getParam(request, "file", "/Album1/image1.jpg");
		// Required: Width image should be resized to
		int width = Integer.parseInt(getParam(request, "width", "250"));
		// Optional: If specified used, otherwise proportions are calculated
		int height = Integer.parseInt(getParam(request, "width", "0"));

		// Set the mime type of the image
		if ("png".equals(imageOutput))
			response.setContentType("image/png");
		else
			response.setContentType("image/jpeg");

		// Server Location of the image
		String imageLoc = request.getSession().getServletContext().getRealPath(imageRoot) + imageFile;

		try {
			// Read the original image from the Server Location
			BufferedImage bufferedImage = ImageIO.read(new File(imageLoc));
			// Calculate the new Height if not specified
			int calcHeight = height > 0 ? height : (width * bufferedImage.getHeight() / bufferedImage.getWidth());
			// Write the image
			ImageIO.write(createResizedCopy(bufferedImage, width, calcHeight), imageOutput, response.getOutputStream());
		} catch (Exception e) {
			log("Problem with image: " + imageLoc + e);
		}
	}

	BufferedImage createResizedCopy(Image originalImage, int scaledWidth, int scaledHeight) {
		BufferedImage scaledBI = new BufferedImage(scaledWidth, scaledHeight, BufferedImage.TYPE_INT_RGB);
		Graphics2D g = scaledBI.createGraphics();
		g.setComposite(AlphaComposite.Src);
		g.drawImage(originalImage, 0, 0, scaledWidth, scaledHeight, null);
		g.dispose();
		return scaledBI;
	}

	// Check the param if it's not present return the default
	private String getParam(HttpServletRequest request, String param, String def) {
		String parameter = request.getParameter(param);
		if (parameter == null || "".equals(parameter)) {
			return def;
		} else {
			return parameter;
		}
	}
}

Here’s the web.xml servlet definition and mapping:

  
  	image
  	com.photo.gallery.ImageResizer
  	1
  
  
    image
    /image

Images in html would look something like this:

Hopefully I’ve contributed something useful to another lazy developer and this solution works. I have no idea how scalable this solution is, nor do I care, it’s just for a photo album where I needed cleanly resized images. More articles to come later on the album such as customizing and parsing xml from Picasa and a Java-based Ajax photo gallery using JQuery UI, don’t hold your breath though, remember I’m lazy.