How to Print Java Screens

Support for printing a screen was absent in Java 1.0, and added in 1.1, but with a number of bugs, both in the concept and implementation. Some problems remain in the 1.2 version.

The general idea is the same as for drawing to an offscreen buffer. First obtain a "special" Graphics g context, and recreate your screen, using this context for all the regular drawing operations. In the case of an offscreen buffer, the result is drawing into a bitmap or pixelmap.

Here, with a different specialized Graphics context, the result is writing a file of PostScript commands. Since PostScript also has commands like drawString and drawLine, it is more or less a direct translation. You then send this file to a printer that understands PostScript. The result is finally drawing a bitmap on paper.

The standard 1.1 example goes like this:

    Toolkit tk;
    if (null != (tk = Toolkit.getDefaultToolkit ())) {

/* This launches a Print Dialog,
 * that's why it needed aFrame to construct the Dialog.
 * Dialog details depend on platform.
 * There are a set of properties you can pass in and out,
 * but they depend on platform,
 * will someday be standardized they tell us. */

        PrintJob pj = tk.getPrintJob
           (aFrame,
            aFrame.getTitle () + " print",
            (Properties)null);

/* Null if user cancels out -- otherwise go ahead */

        if (null != pj) {

/* Graphics context which produces PostScript code,
 * that can be rendered by a PostScript printer or viewer,
 * instead of actually drawing into a bit map,
 * that shows up on the screen. */

            Graphics pg = pj.getGraphics ();
            if (null != pg) {

/* Do not assume defaults -- set them */

                Font myFont = top.getFont ();
                if (null == myFont)
                    myFont = new Font("Courier", Font.PLAIN, 14);

                pg.setFont(myFont);

/* Walk your tree and render everything into Graphics pg.
 * This method defaults to paint () for Component,
 * but many things override it,
 * especially all peer-based (AWT) components,
 * because they do not **really** draw into g,
 * but g tells them **how** to draw.
 * And here we really do have to draw into g,
 * to generate the PostScript code. */

                top.printAll (pg);

/* The dispose flushes it to be printed,
 * or closes the file if that was the destination. */

                pg.dispose ();
            }

/* We could get another pg and print another page... */

            pj.end ();
        }
    }

• printAll -- some of the peer-based AWT components have buggy printAll methods, and draw things twice or not at all, or in the wrong place. Some of them throw null-pointer exceptions, effectively cutting short your output, even if you have try / catch wrapped around the top level printAll, so that your program doesn't crash outright. There were once similar problems drawing to an offscreen image, but those have been fixed long ago.
  Sun continues to get this wrong in every release. They now appear to have put it into their "not our problem" list, both for AWT and the newer Swing components.
  Their latest answer http://developer.java.sun.com/developer/onlineTraining/Programming/JDCBook/render.html is to use your own rendering and tree-walker code, such as provided here.
• PrintJob -- locks you into generating PostScript output, as in the example above. You cannot render to other formats, such as GIF or JPG.
  The sun.image package available in JDK 1.2, does support JPG output, but there is still no support for GIF output, and of course it is not an "offical" part of the release, so it could be changed or dropped at any time.
• There is no PrintJob support for printing other files that your program has produced, such as a log or journal. Too bad, because this dialog does give you access to network printers, something the program should be able to do.
  PrintJob has a "FileName" property you can set, but this is NOT how to print some other file, it is just the default name if the user prints to a file.
• PrintJob again -- does not handle page sizes properly. It may or may not tell you the correct page size, with or without subtracting for margins. In fact, it should scale your entire output to fit the page, which is a lot better than making you revise your layout.
  The page dimensions are in points (1/72 inch) not pixels, but all the AWT dimensions will take them as pixels, so expect some change in size.

I have been able to work around these problems, with the aid of some code that others have written, copyrighted, and shared with the public.

PSGr

PSGr (the PostScript Graphics Context) implements all public methods of the Graphics class, for example drawRect () and drawString () but instead of drawing on the screen, it writes a file of the equivalent PostScript commands for printing. Unlike the awt offering, PSGr offers additional (non-Graphics) public methods related to PostScript, with scale () the one of most interest here. PSGr was written and is copyright by Ernest Friedman-Hill email at ejfried@ca.sandia.gov I did the port from 1.0 to 1.1 Java, that is available here.

JpegEncoder

JpegEncoder processes an Image, and produces a compressed JPEG encoding of that Image. For our purpose, the Image will be an OffScreenImage, for which we can do getGraphics (), and into which we draw to replicate the Java screen. JpegEncoder was written and is copyright by James R weeks email at james@obrador.com

GifEncoder.java

Produces a GIF compressed encoding of an Image, again for our purpose, an OffScreenImage, into which we have replicated the Java screen. Written and Copyright (C) 1996 by Jef Poskanzer email at jef@acme.com

I have made two minor but useful additions to GifEncoder:

• Nearest-color sharing, if the on-screen Image has more than the 256 colors allowed by the GIF standard. This retains the first 256 colors found by scanning the image, and maps any others to the closest fit. There is no promise that the first 256 colors are the best subset, but it usually works out pretty well.
• Clipping, to encode only a specified Rectangle, perhaps as user-specified by a rubber-band box, rather than the entire Image. See Cropper.java as an example using this feature.

ImageEncoder.java

Base class for GifEncoder, and for some other encoders too. See the acme site.

IntHashtable.java

Support class for GifEncoder.

BitmapEncoder.java

Produces a Microsoft Windows Bitmap Encoding. Again for our purpose, from an OffScreenImage, into which we have replicated the Java screen. Written by Jean-Pierre Dubé, and presented as Java Tip 60, by Javaworld

LoadBitmap.java

LoadBitmap is not part of this demo, it is for input rather than output. It allows your Java program to load and display a Microsoft Windows Bitmap Encoded image, as easily as a GIF or JPG image. Written by Jeff West, with John D. Mitchell, and presented as Java Tip 43, by Javaworld

What I am doing here is trying to make these classes better known, providing an example of their use, and also providing some additional useful code. I want to stress that this is not a "mirror site" or support site for these classes, and I certainly am not taking credit for them.

If you find them useful, by all means thank the original authors, and please let me know too. If you have any problems with the code presented here, please write to me, and do not bother the original authors.

You might want to visit the original sites, and see if they have newer versions.

You also might want to drop Sun a note, and ask why they still don't provide these things.

Because applets are not allowed to print or save files, the example is written as an application. You will have to download the sources and compile it.

• PrintDemo.java
• Cropper.java
• ListenerAdder.java
• Util.java
• PSGr.java
• JpegEncoder.java
• GifEncoder.java
• ImageEncoder.java
• IntHashtable.java
• PSPrint.java
• BitmapEncoder.java
• LoadBitmap.java

Please see my otherJava Techniques

Please also visit theMorris Hirsch home page.

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Finally, if you did NOT find this page useful, or you think the information is out of date, or you know other information that should be mentioned here, please let me know that too. Email me at morris_hirsch@brown.edu

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