JDK 1.2 does JPEG

JDK 1.2 is a major upgrade for the Java platform. It officially introduces Swing, the advanced widget library. It also adds support for CORBA, the standard object-oriented middleware protocol, and it defines a new API for graphics, Java 2D, as well as many, many other enhancements.

Buried in all these novelties is a JPEG codec. As the name implies, a JPEG codec encodes bitmaps as JPEG files. Java could read JPEG or GIF files since the early JDK days, but there was no built-in method to save bitmaps — until now.

The ability to save bitmaps is not only important for graphics applications. Any application that prepares data for publishing on the Internet will benefit from the JPEG codec. However, servlets will benefit the most.

Servlets

Servlets are typically used with HTML forms. However, this is not a limitation. Servlets can be used to dynamically create files of any type: HTML, JPEG, GIF, XML, and so forth. In fact, there are many applications where you want to dynamically create graphics: hit counters, business charts, electronic postcards or to nicely present data, such as a game score.

The JPEG codec

Writing a JPEG from Java is easy, as illustrated by listing 1. First, create a JPEG codec, set some parameters and call

encode()

The application controls the quality of the image though parameters. Unlike GIF, JPEG is lousy at encoding, i.e., it will degrade the image to achieve better compression. The quality ratio determines how much degradation is acceptable. Unfortunately, one has to choose between the quality of the image and its size. The smaller the image, the lower the quality. Common values for the quality ratio are: 1.0 for no degradation, 0.75 for high quality images, 0.5 for medium quality, and 0.25 for very high compression with low-quality images. Although 0.75 is most commonly used, the correct ratio depends on the application’s needs.

Listing 1: Encoding BufferedImage in JPEG

public void encode(BufferedImage img,

                   OutputStream out)

   throws IOException

{

   JPEGImageEncoder encoder =

      JPEGCodec.createJPEGEncoder(out);

   JPEGEncodeParam param =

      encoder.getDefaultJPEGEncodeParam(img);

   param.setQuality(0.75f,true);

   encoder.encode(img,param);

}

A hit counter

A servlet inherits from HttpServlet. The Web server calls the

doGet()

init()

destroy()

The interesting code is in

doGet()

The drawing code uses the new Java 2D API, which is an extension of AWT and, therefore, should be familiar to Java programmers. A new class, Graphics2D, adds new methods to the familiar AWT Graphics. When running under JDK 1.2, an application should use Graphics2D where it formerly used Graphics.

One of the new methods is

setRenderingHint()

The servlet also uses the new TextLayout class for finer control over the placement of text.

Listing 2: The WebCounter servlet

package com.psol.author;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;
import java.awt.*;

import java.awt.font.*;

import java.awt.geom.*;

import java.awt.image.*;

import com.sun.image.codec.jpeg.*;
public class WebCounter extends HttpServlet

{

   protected int count = 0;

   protected final static int WIDTH = 50,

                              HEIGHT = 18,

                              FONTSIZE = 14;

   protected final static String FONTNAME = “Arial”,

                                 FILENAME = “webcounter.data”;
   public void init(ServletConfig config)

      throws ServletException

   {

      super.init(config);

      try

      {

         DataInputStream in =

            new DataInputStream(

               new FileInputStream(FILENAME));

         count = in.readInt();

      }

      catch(IOException x)

         {}

   }
   public void destroy()

   {

      try

      {

         DataOutputStream out =

            new DataOutputStream(

               new FileOutputStream(FILENAME));

         out.writeInt(count);

      }

      catch(IOException x)

         {}

   }
   public void doGet(HttpServletRequest request,

                     HttpServletResponse response)

      throws ServletException, IOException

   {

      response.setContentType(“image/jpeg”);

      BufferedImage img = draw(Integer.toString(++count));

      OutputStream out = response.getOutputStream();

      JPEGImageEncoder encoder =

         JPEGCodec.createJPEGEncoder(out);

      JPEGEncodeParam param =

         encoder.getDefaultJPEGEncodeParam(img);

      param.setQuality(1.0f,true);

      encoder.encode(img,param);

      out.close();

   }
   protected BufferedImage draw(String st)

   {

      BufferedImage img =

         new BufferedImage(WIDTH,HEIGHT,

                           BufferedImage.TYPE_INT_RGB);

      Graphics2D g2 = img.createGraphics();

      g2.setBackground(Color.orange);

      g2.clearRect(0,0,WIDTH,HEIGHT);

      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

                          RenderingHints.VALUE_ANTIALIAS_ON);

      g2.setColor(Color.black);

      Font font = new Font(FONTNAME,Font.PLAIN,FONTSIZE);

      g2.setFont(font);

      TextLayout tl =

         new TextLayout(st,font,

                        g2.getFontRenderContext());

      Rectangle2D r = tl.getBounds();

      // center the text

      tl.draw(g2,(float)((WIDTH – r.getWidth()) / 2),

                 (float)(((HEIGHT – r.getHeight()) / 2) +

                     r.getHeight()));

      g2.dispose();

      return img;

   }
   public String getServletInfo()

   {

      return “WebCounter by B. Marchal for developer.com”;

   }

}