15.3.1. Installation

15.3.2. Class Generation

Figure 15-3. The Zeus methodology of class generation

Once you've got that, use the following command for class generation:

C:\javaxml2\build>java samples.TestSchemaBinder 
    -file=c:\javaxml2\ch14\xml\zeus\catalog.xsd 
    -package=javaxml2.zeus 
    -quiet=true

You'll get identical output using either a DTD or a schema.

WARNING: This is a slight overstatement. Actually, you will get identical output if you can represent the constraints in the DTD and XML Schema identically. In this example, the schema defines "level" as an integer, while the DTD must define it as PCDATA. The result is that using a schema, you get a typed level (a Java int), and using a DTD, you get a String. I've used the DTD version throughout this section, to show you that option.

Within the output directory, you'll find a javaxml2 directory, and then a zeus directory (matching up to the package hierarchy). You can take a look at the source files generated within.

Right off, you should notice that Zeus produces an interface (for example, Catalog.java) and a default implementation of that interface (for example, CatalogImpl.java). The reasoning behind this, as opposed to the concrete classes that Castor generates, is that you may want to have your own custom classes, perhaps already in existence, that implement the Catalog interface. You can therefore use your own implementation, but get the benefits of class generation. I commonly see developers using Zeus to generate classes and then creating their own implementation of the generated interfaces as Enterprise JavaBeans (EJBs). These EJBs are then persisted using Zeus, which is a piece of cake (as I'll show you in the next section). Without providing for user-defined implementations, this behavior would require modifying the generated source code, which could break marshalling and unmarshalling.

Another notable difference you should be aware of is the method names. For example, here's the Item interface (trimmed down to its simplest form):

package javaxml2.zeus;

public interface Item {

    public Title getTitle( );
    public void setTitle(Title title);

    public Teacher getTeacher( );
    public void setTeacher(Teacher teacher);

    public java.util.List getGuestList( );
    public void setGuestList(java.util.List guestList);
    public void addGuest(Guest guest);
    public void removeGuest(Guest guest);

    public Description getDescription( );
    public void setDescription(Description description);

    public String getLevel( );
    public void setLevel(String level);

    public String getId( );
    public void setId(String id);
}

Notice that the JavaBeans naming is used, and elements that can appear multiple times are returned as Java 2 Collections classes. In any case, take a look at this source, and then compile it:

javac -d . output/javaxml2/zeus/*.java

Now you're ready to look at marshalling and unmarshalling using Zeus.

15.3.3. Marshalling and Unmarshalling

File catalogFile = new File("catalog.xml");
FileReader reader = new FileReader(catalogFile);
FileWriter writer = new FileWriter(catalogFile);

// Castor: Unmarshalling
Catalog catalog =
    (Catalog)org.exolab.castor.xml.Unmarshaller.unmarshal(Catalog.class, reader);

// Zeus: Unmarshalling
StreamSource source = new StreamSource(reader);
org.enhydra.zeus.Unmarshaller unmarshaller = new org.enhydra.zeus.Unmarshaller( );
Catalog catalog = (Catalog)unmarshaller.unmarshal(source);

// Castor: Marshalling
org.exolab.castorMarshaller.marshal(catalog, writer);

// Zeus: Marshalling
StreamResult result = new StreamResult(writer);
org.enhydra.zeus.Marshaller marshaller = new org.enhydra.zeus.Marshaller( );
marshaller.marshal(catalog, result);

This reads in the file specified, and then spits out the ID and title of each item in the catalog. It also checks for a certain ID ("CDZ-SM01"), and modifies that item to reflect a second edition (and all of us around here love second editions!). Finally, it writes the catalog back out to a new file, with the modified information. Try it out; just be sure that you already have the compiled Zeus-generated classes in your classpath.