Multiple JAXBContext instances

Question

By using XJC, I create 2 different JAXB metadata packages with an ObjectFactory class in each package (I dont know if this approach is OK, I have 2 different XSD's to work on )

It is recommended to create only one JAXBContext per operation, because it is costy. So I wonder if what I'm doing here is valid and good practise?

    JAXBContext jaxbContext = JAXBContext.newInstance("com.package.one");
    Unmarshaller jaxbUnmarshaller1 = jaxbContext.createUnmarshaller();

    JAXBContext jaxbContext2 = JAXBContext.newInstance("com.package.two");
    Unmarshaller jaxbUnmarshaller2 = jaxbContext2.createUnmarshaller();

EDIT when i try to initialize 2 packages together i get an exception "The element name {}Value has more than one mapping." Value is a class in both packages.

 JAXBContext jaxbContext = JAXBContext.newInstance("com.package.one:com.package.two");

Answer 1

From the Javadoc for JAXBContext:

A client application normally obtains new instances of this class using one of these
two styles for newInstance methods, although there are other specialized forms of the
method available:

JAXBContext.newInstance( "com.acme.foo:com.acme.bar" )
The JAXBContext instance is initialized from a list of colon separated Java package
names. Each java package contains JAXB mapped classes, schema-derived classes and/or
user annotated classes. Additionally, the java package may contain JAXB package annotations
that must be processed. (see JLS 3rd Edition, Section 7.4.1. Package Annotations).

JAXBContext.newInstance( com.acme.foo.Foo.class )
The JAXBContext instance is intialized with class(es) passed as parameter(s) and
classes that are statically reachable from these class(es). See newInstance(Class...)
for details.

You can use a shared context and initialize it with a list of package names.

Code Example:

package test.jaxb.one;

@XMLRootElement
@XMLType(name = "test.jaxb.one.SimpleObject")
@XMLAccessorType(XMLAccessType.FIELD)
public class SimpleObject implements Serializable {
    private static final long serialVersionUID = 54536613717262557148L;

    @XmlElement(name = "Name")
    private String name;

    // Constructor, Setters/Getters
}

and this one:

package test.jaxb.two;

@XMLRootElement
@XMLType(name = "test.jaxb.two.SimpleObject")
@XMLAccessorType(XMLAccessType.FIELD)
public class SimpleObject implements Serializable {
    private static final long serialVersionUID = -4073071224211934153L;

    @XmlElement(name = "Name")
    private String name;

    // Constructor, Setters/Getters
}

Finally:

public class JAXBTest {
    @Test
    public void testContextLoad() throws Exception {
        final JAXBContext context = JAXBContext
            .newInstance("test.jaxb.one:test.jaxb.two");
        Assert.assertNotNull(context);
    }
}