Revision as of 12:51, 28 July 2010

Dynamic MOXy - Bootstrapping from EclipseLink Externalized Metadata (OXM)

ER 321152

Document History

Overview

The purpose of this feature is to allow the user to bootstrap EclipseLink Dynamic JAXB from an EclipseLink externalized metadata file (eclipselink-oxm.xml). This is a continuation of the Dynamic JAXB features introduced in EclipseLink 2.1.0.

Support for bootstrapping a DynamicJAXBContext from an EclipseLink Externalized Metadata file (OXM) will be implemented in multiple phases. For each phase, OXM files will be created that will exercise the associated annotations. A DynamicJAXBContext will be created from each OXM file, and an example object will be marshalled. The resulting document will be inspected to ensure that it was marshalled properly, according to the annotations being tested.

See also: Dynamic JAXB Documentation

Generating a DynamicJAXBContext with OXM

A DynamicJAXBContext is created from an XSD in the following way:

1. The OXM file is parsed by JAXBContextFactory to generate an org.eclipse.persistence.jaxb.xmlmodel.XmlBindings object.
2. The XmlBindings are inspected and an EclipseLink javamodel representing this information is created.
3. This collection of EclipseLink javamodel classes is then passed to org.eclipse.persistence.jaxb.compiler.Generator, which generates a standard EclipseLink project.
4. A Dynamic Project is then created from the standard project via DynamicTypeBuilder.loadDynamicProject().
5. An org.eclipse.persistence.oxm.XMLContext is then created from the Dynamic Project, and a DynamicJAXBContext is returned backed by this XMLContext.

Development Phases

Phase 1

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="US-ASCII"?>
<xml-bindings xmlns="http://www.eclipse.org/eclipselink/xsds/persistence/oxm">
    <java-types>
        <java-type name="mynamespace.Person">
            <xml-root-element name="person"/>
            <java-attributes>
                <xml-element type="java.lang.String" java-attribute="type" xml-path="bloodType/text()"/>
            </java-attributes>
        </java-type>
    </java-types>
</xml-bindings>

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Limitations

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Phase 2

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

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Limitations

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Phase 3

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

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Limitations

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Phase 4

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

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Limitations

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Phase 5

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

• Text.
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Limitations

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Phase 6

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

• Text.
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Limitations

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Phase 7

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

• Text.
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Limitations

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Phase 8

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

• Text.
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Limitations

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Phase 9

The following example OXM file demonstrates how these annotations can be specified:

Example OXM

<?xml version="1.0" encoding="UTF-8"?>

• Text.
• Text.

Limitations

• Text.

Design

When constructing a DynamicJAXBContext from an OXM file, we will first parse the metadata in order to create our own EclipseLink JavaModel classes, then pass this code model into an EclipseLink Generator (org.eclipse.persistence.jaxb.compiler.Generator) to generate an EclipseLink project. After we have created this project, we can use the DynamicTypeBuilder to create a dynamic project, generating Java classes in memory along the way.

First, we use internal EclipseLink API to parse the OXM file and return an XmlBindings object:

Map<String, XmlBindings> bindings = JAXBContextFactory.getXmlBindingsFromProperties(properties, classLoader);
 
JavaClass[] elinkClasses = createClassModelFromOXM(bindings);
 
...
private JavaClass[] createClassModelFromOXM(Map<String, XmlBindings> bindings) throws JAXBException {
    List<OXMJavaClassImpl> oxmJavaClasses = new ArrayList<OXMJavaClassImpl>();
 
    Iterator<String> keys = bindings.keySet().iterator();
 
    while (keys.hasNext()) {
        XmlBindings b = bindings.get(keys.next());
 
        List<JavaType> javaTypes = b.getJavaTypes().getJavaType();
        for (Iterator<JavaType> iterator = javaTypes.iterator(); iterator.hasNext();) {
            JavaType type = iterator.next();
            oxmJavaClasses.add(new OXMJavaClassImpl(type));
        }
    }
    ...

At this point, we can instantiate a Generator and obtain a "dry" EclipseLink project, which we can then turn into a dynamic project with generated in-memory classes. Finally, we create and store an XMLContext and a DynamicHelper:

// Use the JavaModel to setup a Generator to generate an EclipseLink project
OXMJavaModelImpl javaModel = new OXMJavaModelImpl(classLoader, elinkClasses);
OXMJavaModelInputImpl javaModelInput = new OXMJavaModelInputImpl(elinkClasses, javaModel);
Generator g = new Generator(javaModelInput, bindings, dynamicClassLoader, null);
 
Project p = null;
Project dp = null;
try {
    p = g.generateProject();
    // Clear out InstantiationPolicy because it refers to ObjectFactory, which we won't be using
    Vector<ClassDescriptor> descriptors = (Vector<ClassDescriptor>) p.getOrderedDescriptors();
    for (ClassDescriptor classDescriptor : descriptors) {
        classDescriptor.setInstantiationPolicy(new InstantiationPolicy());
    }
    dp = DynamicTypeBuilder.loadDynamicProject(p, null, dynamicClassLoader);
} catch (Exception e) {
    throw new JAXBException(org.eclipse.persistence.exceptions.JAXBException.errorCreatingDynamicJAXBContext(e));
}
 
this.xmlContext = new XMLContext(dp);
 
List<Session> sessions = (List<Session>) this.xmlContext.getSessions();
for (Object session : sessions) {
    this.helpers.add(new DynamicHelper((DatabaseSession) session));
}