Revision as of 11:02, 5 April 2011

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Dynamic Bootstrapping (Single Project) from sessions.xml (EclipseLink project)

With EclipseLink dynamic MOXy, you can bootstrapping from an EclipseLink project specified in sessions.xml file. In this scenario, your specifies only Java class names -- not the actual Java classes, as shown here:

CORRECT:

customerDescriptor.setJavaClassName("mynamespace.Customer");
...
addressMapping.setReferenceClassName("mynamespace.Address");

INCORRECT: <sorce lang="java"> customerDescriptor.setJavaClass(mynamespace.Customer.class); ... addressMapping.setReferenceClass(mynamespace.Address.class); </source>

You map these "imaginary" classes to XML. EclipseLink dynamically generates the classes in memory, when buildingn the DynamicJAXBContext.

Add your EclipseLink project to the EclipseLink sessions.xml file. Use the following API to pass the session's name to the DynamicJAXBContextFactory and create your DynamicJAXBContext:

/**
 * Create a <tt>DynamicJAXBContext</tt>, using an EclipseLink <tt>sessions.xml</tt> as the metadata source.
 * The <tt>sessionNames</tt> parameter is a colon-delimited list of session names within the
 * <tt>sessions.xml</tt> file.  <tt>Descriptors</tt> in this session's <tt>Project</tt> must <i>not</i>
 * have <tt>javaClass</tt> set, but <i>must</i> have <tt>javaClassName</tt> set.
 *
 * @param sessionNames
 *      A colon-delimited <tt>String</tt> specifying the session names from the <tt>sessions.xml</tt> file.
 * @param classLoader
 *      The application's current class loader, which will be used to first lookup
 *      classes to see if they exist before new <tt>DynamicTypes</tt> are generated.  Can be
 *      <tt>null</tt>, in which case <tt>Thread.currentThread().getContextClassLoader()</tt> will be used.
 * @param properties
 *      Map of properties to use when creating a new <tt>DynamicJAXBContext</tt>.  Can be null.
 *
 * @return
 *      A new instance of <tt>DynamicJAXBContext</tt>.
 *
 * @throws JAXBException
 *      if an error was encountered while creating the <tt>DynamicJAXBContext</tt>.
 */
public static DynamicJAXBContext createContext(String sessionNames, ClassLoader classLoader, 
   Map<String, ?> properties) throws JAXBException

[edit] Example

Here is an example of an EclipseLink MOXy Project in code. Notice that we have customizations that are made:

   * We have specified that the package name of the generated classes should be com.mypackage. If importing from XSD, we would have used the default namespace to build the package name instead, which would result in a package name of mynamespace.
   * We have specified that the first-name element in XML should be mapped to a field called fName in Java. If importing from XSD we would have generated a field called firstName.
   * We have specified that a null address will be represented by xsi:nil="true" in XML. 

package mynamespace;

import org.eclipse.persistence.oxm.NamespaceResolver; import org.eclipse.persistence.oxm.XMLConstants; import org.eclipse.persistence.oxm.XMLDescriptor;

import org.eclipse.persistence.oxm.mappings.XMLDirectMapping; import org.eclipse.persistence.oxm.mappings.XMLCompositeObjectMapping;

public class CustomerProject extends org.eclipse.persistence.sessions.Project {

  public CustomerProject() {
     super();

     NamespaceResolver nsResolver = new NamespaceResolver();
     nsResolver.put("ns0", "mynamespace");
     nsResolver.put("xsi", XMLConstants.SCHEMA_INSTANCE_URL);

     XMLDescriptor customerDescriptor = new XMLDescriptor();
     customerDescriptor.setJavaClassName("mynamespace.Customer");
     customerDescriptor.setDefaultRootElement("customer");
     customerDescriptor.setNamespaceResolver(nsResolver);

     XMLDirectMapping firstNameMapping = new XMLDirectMapping();
     firstNameMapping.setAttributeName("fName");
     firstNameMapping.setXPath("first-name/text()");
     customerDescriptor.addMapping(firstNameMapping);
     // ...

     XMLCompositeObjectMapping addressMapping = new XMLCompositeObjectMapping();
     addressMapping.setAttributeName("address");
     addressMapping.setXPath("address");
     addressMapping.setReferenceClassName("mynamespace.Address");
     addressMapping.getNullPolicy().setNullRepresentedByXsiNil(true);
     addressMapping.getNullPolicy().setMarshalNullRepresentation(XMLNullRepresentationType.XSI_NIL);
     customerDescriptor.addMapping(addressMapping);

     XMLDescriptor addressDescriptor = new XMLDescriptor();
     addressDescriptor.setJavaClassName("mynamespace.Address");
     // ...

     this.addDescriptor(customerDescriptor);
     this.addDescriptor(addressDescriptor);
  }

}

Next, here is an example sessions.xml that includes our Project:

<?xml version="1.0" encoding="US-ASCII"?> <sessions xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" ...>

  <session xsi:type="database-session">
     <name>MyCustomerProject</name>
     <primary-project xsi:type="class">mynamespace.CustomerProject</primary-project>
  </session>

</sessions>

Finally, we can now instantiate a DynamicJAXBContext using the session name, and begin working with our DynamicEntities:

DynamicJAXBContext dContext = DynamicJAXBContextFactory.createContext("MyCustomerProject", null, null);

DynamicEntity newCustomer = dContext.newDynamicEntity("com.mypackage.Customer"); newCustomer.set("fName", "Bob"); ... dContext.createMarshaller().marshal(newCustomer, System.out);

You may specify multiple Session names when bootstrapping from an EclipseLink Project. For example,

DynamicJAXBContextFactory.createContext("ProjectA:ProjectB", null, null);

would create a single DynamicJAXBContext that is aware of Mappings and Descriptors from both Projects.

From OXM	From a single project	From multiple projects
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