Creating and Modifying XML Documents - Beginning Java 2 SDK - page 1071

System.err.println(e.getMessage());
e.printStackTrace(System.err);
return null;

} catch(DOMException e) {
JOptionPane.showInternalMessageDialog(null,
"DOM exception thrown while creating document",
"DOM Error",
JOptionPane.ERROR _ MESSAGE);
System.err.println(e.getMessage());
e.printStackTrace(System.err);
return null;
}

// Each element in the sketch can create its own node in the document
Iterator iter = getIterator(); // Iterator for sketch elements
while(iter.hasNext()) // For each element...
((Element)iter.next()).addElementNode(doc); // ...add its node.
return doc;
}

Now notice that this requires the DTD file for sketcher in the same folder as a saved sketch. In our case,
we've made the default c:\sketches so a copy will need to be present there.

We now pop up a dialog and return null if something goes wrong when we are creating the Document
object. In case of an exception of type DOMException being thrown, you could add a switch
statement to analyze the value in the code member of the exception and provide a more specific
message in the dialog.

The SketchModel object can now create a DOM Document object encapsulating the entire sketch.
All we now need is some code to use this to write an XML file.

Saving a Sketch as XML
Of course, we could modify Sketcher so that it could save sketches either as objects or as XML, but to
keep things simple we will add menu items to the F ile menu to export or import a sketch as XML. In
broad terms, here's what we have to do to the SketchFrame class to save a sketch as an XML file:

Add Import XML and Export XML menu items. ❑

Add XML ImportAction and XMLExportAction inner classes defining the Action types
for the new menu items, either to save the current sketch as an XML file or to replace the
current sketch by a new sketch created from an XML file.

❑

Implement the process of creating an XML document as text from the Document object
created by the createDocument() method that we added to the SketchModel class.

❑

Implement writing the text for the XML document to a file.

❑