This section explains how to manipulate the DOM tree of an SVG
document from a Java program. It contains the following
sub-sections:
How to manipulate a JSVGCanvas' document?
How to write thread-safe code?
Using the SVG DOM
How to run Java code using a <script> element?
The follow code template demonstrates how to manipulate an SVG
document displayed in a JSVGCanvas directly from a Java program.
You don't have to worry about graphics updates:
after each event listener invocation the canvas is updated
if needed.
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import org.apache.batik.swing.JSVGCanvas;
import org.apache.batik.swing.svg.SVGLoadEventDispatcherAdapter;
import org.apache.batik.swing.svg.SVGLoadEventDispatcherEvent;
import org.apache.batik.script.Window;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.events.Event;
import org.w3c.dom.events.EventListener;
import org.w3c.dom.events.EventTarget;
public class SVGApplication {
public static void main(String[] args) {
new SVGApplication();
}
JFrame frame;
JSVGCanvas canvas;
Document document;
Window window;
public SVGApplication() {
frame = new JFrame();
canvas = new JSVGCanvas();
// Forces the canvas to always be dynamic even if the current
// document does not contain scripting or animation.
canvas.setDocumentState(JSVGCanvas.ALWAYS_DYNAMIC);
canvas.addSVGLoadEventDispatcherListener
(new SVGLoadEventDispatcherAdapter() {
public void svgLoadEventDispatchStarted
(SVGLoadEventDispatcherEvent e) {
// At this time the document is available...
document = canvas.getSVGDocument();
// ...and the window object too.
window = canvas.getUpdateManager().
getScriptingEnvironment().createWindow();
// Registers the listeners on the document
// just before the SVGLoad event is
// dispatched.
registerListeners();
// It is time to pack the frame.
frame.pack();
}
});
frame.addWindowListener(new WindowAdapter() {
public void windowOpened(WindowEvent e) {
// The canvas is ready to load the base document
// now, from the AWT thread.
canvas.setURI("doc.svg");
}
});
frame.getContentPane().add(canvas);
frame.setSize(800, 600);
frame.show();
}
public void registerListeners() {
// Gets an element from the loaded document.
Element elt = document.getElementById("elt-id");
EventTarget t = (EventTarget)elt;
// Adds a 'onload' listener
t.addEventListener("SVGLoad", new OnLoadAction(), false);
// Adds a 'onclick' listener
t.addEventListener("click", new OnClickAction(), false);
}
public class OnLoadAction implements EventListener {
public void handleEvent(Event evt) {
// Make some actions here...
// ...for example start an animation loop:
window.setInterval(new Animation(), 50);
}
}
public class OnClickAction implements EventListener {
public void handleEvent(Event evt) {
// Make some actions here...
// ...for example schedule an action for later:
window.setTimeout(new DelayedTask(), 500);
}
}
public class Animation implements Runnable {
public void run() {
// Insert animation code here...
}
}
public class DelayedTask implements Runnable {
public void run() {
// Make some actions here...
// ...for example displays an alert dialog:
window.alert("Delayed Action invoked!");
}
}
}
The DOM listeners registered on the SVG document are called from
the canvas update thread. To avoid race conditions do not manipulate
the DOM tree from another thread.
The way to switch from an external thread to the canvas update
thread is to use the following code:
// Returns immediately
canvas.getUpdateManager().getUpdateRunnableQueue().
invokeLater(new Runnable() {
public void run() {
// Insert some actions on the DOM here
}
});
- or -
// Waits until the Runnable is invoked
canvas.getUpdateManager().getUpdateRunnableQueue().
invokeAndWait(new Runnable() {
public void run() {
// Insert some actions on the DOM here
}
});
Like with event listeners, when a Runnable is invoked from the
update thread, the graphics are updated.
It is very dangerous to call 'invokeAndWait' from the
Swing Event thread. This is the only thread that can be
used to interact with Swing components. In some cases
DOM calls may need to query the canvas for information
(such as actual Swing component size etc). If this
happens you will get a thread deadlock. You should
only make invokeAndWait calls from 'third party' threads.
Batik provides a fairly complete implementation of the
SVG DOM. The SVG DOM provides all the functionality most
applications require. In particular the DOM implements
DOM Events including mutation and UI Events.
DOM events allow you to get notified when the cursor
moves over elements of interest:
// Element of Interest.
Element theElem;
((EventTarget)theElem).addEventListener("mouseover", mouseOverListener, true);
Where mouseOverListener implements the
org.w3c.dom.events.EventListener interface.
This interface consists of the method:
public void handleEvent(Event evt);
This is called whenever the event occurs with the
element it is registered on. It is worth reviewing the
DOM Events specification as there are many useful features
to this interface that are not immediately obvious.
It is also worth looking at the DOM interfaces defined
by the SVG specification as they provide a large number
of useful methods, in particular the SVGLocatable:
// Returns Bounding box of SVG Element.
public SVGRect getBBox ( );
// Returns the transformation matrix to the screen.
public SVGMatrix getScreenCTM ( );
// Returns the transformation matrix to the given element.
public SVGMatrix getTransformToElement ( SVGElement element )
throws SVGException;
In particular getScreenCTM is very useful for
taking the 'clientX', 'clientY' attributes of the
DOM UIEvent and mapping them to the coordinate system
of an element in the SVG document:
Batik provides an extension of the SVG
<script> element which allows Java programs
to be called from an SVG document.
This feature is available to any application of Batik that uses
the bridge module (for example the Swing component and the
transcoders).
In order to use this extension, the type attribute
of a <script> element must be set to
application/java-archive. In addition the
xlink:href attribute must be the URI of a jar file
which contains the program to run.
The manifest of this jar file must contains an entry of the form:
SVG-Handler-Class: classname
Where classname must be the name of a class which
implements the
org.w3c.dom.svg.EventListenerInitializer interface.
See the javadoc of this interface for more details.
The class can be contained directly in the jar file, but it is
also possible for it to be contained in a jar file added to the
classpath using the Class-Path entry of the
manifest.