Sergey Groznyh's Blog

September 2007 Archives

Generating Print Preview of Swing Text Components

This question, “how to generate print preview of Java Swing components,” is asked often on various discussion forums, because currently (as of version 6) the Java SE doesn't have standard facilities for building print previews. While working on the Swing Tutorial, I tried to address this issue under the topic “Using JTextComponent.getPrintable method.” This will hopefully appear in the updated version of the Swing Tutorial for JDK6. In the meantime, I'll put the relevant information here.

There exist several resources on the Internet related to generating print previews in Java, but in most cases they are either commercial, or use an outdated API, or attempt to build some all-in-one custom dialog solution without paying much attention to details. In this issue I'll try to focus on how to create a print preview—what necessary parts are involved and how they do communicate.

What to Print

The JTextComponent class defines the getPrintable method which returns an instance of the Printable interface containing a single method, print. Assuming the textComponent is a JTextComponent object we are going to generate print preview for, the following code shows how to obtain a Printable instance out of it.

Printable p = textComponent.getPrintable();

Page Format

Next thing we need to know is the parameters of the output media, most important ones being the physical page dimensions. In real-life situation the available page dimensions should be obtained by querying some PrintService known to your Java environment. For the purposes of this example we'll just use the default page format.

PageFormat f = new PageFormat();
int pageWidth = f.getWidth();
int pageHeight = f.getHeight();

Where to Print

Then we need a print destination that will receive the actual drawing commands. The destination should be an instance of the Graphics class. A simple way of obtaining this is using the BufferedImage class as physical backing store. This class defines the getGraphics method which returns a Graphics instance.

Image page = new BufferedImage(
        pageWidth, pageHeight, BufferedImage.TYPE_INT_ARGB);
Graphics g = page.getGraphics();

How to Print

Now we are ready to generate page images. We need to repeatedly invoke the print method on the Printable instance, specifying the page number to print (0 is the first page) and the Graphic and PageFormat objects. The print method returns some status code. The value of PAGE_EXISTS indicates the success of the operation.

for (int n = 0; p.print(g, f, n) == Printable.PAGE_EXISTS; n++) {
    // N-th page printed successfully
}

How to Scale

The generated page image is usually too large for on-screen display, so we need to shrink the image for viewing. The following code creates an image with size reduced by two times on both dimensions.

double scaleFactor = 0.5;
int previewWidth = (int) (pageWidth * scaleFactor);
int previewHeight = (int) (pageHeight * scaleFactor);
Image preview = page.getScaledInstance(
        previewWidth, previewHeight, SCALE_SMOOTH);

Back to Swing

Until now we dealt mostly with 2D and AWT parts of the Client Java API. Now we need to place the generated preview image into some Swing component. For this we'll create a subclass of the JPanel, implementing the custom paintComponent method and overriding the getPreferredSize, getMinimumSize and getMaximumSize methods so our preview component is laid out correctly.

JPanel previewPane = new JPanel() {
    public void paintComponent(Graphics g) {
        g.drawImage(preview, 0, 0, previewWidth, previewHeight, null);
    }

    public Dimension getPreferredSize() {
        return new Dimension(previewWidth, previewHeight);
    }

    public Dimension getMinimumSize() {
        return getPreferredSize();
    }

    public Dimension getMaximumSize() {
        return getPreferredSize();
    }
}

The resulting print preview pane can then be added to Swing container, just like any other Swing component.

Below are links to the example containing the complete print preview implementation as described in this issue. Using this implementation, the print preview functionality could be added to any text component in a couple lines of code.

Please note that in order to run this demo, you'll need Java runtime version 1.6 (aka 6.0) or higher.

The demo displays a chapter from “Alice in Wonderland” in the JEditorPane component. Print preview window could be activated from menu or by using a keyboard shortcut. Standard Java Print Dialog could be invoked from inside the print preview.

This work is licensed under a Creative Commons License.