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Object Content Manager

The main component in the OCM framework is the ObjectContentManager. It converts an object graph into JCR nodes and properties and vice versa. The ObjectContentManager is always associated with a JCR Session. It is used to retrieve, create, update and delete objects from a JCR content repository. Usually there is one ObjectContentManager per user session.

This page describes how an ObjectContentManager is working and how it can be initialised in your applications.

How does the Object Content Manager work ?

Thanks to a Mapping Descriptor, the ObjectContentManager is able to use the appropriate mapping strategy for each persistent object (pojo). The Mapping Descriptor contains one Class Descriptor per persistent class. Each Class Descriptor contains mapping information for the corresponding class attributes.

In the point of view implementation, the Mappring Descriptor is a java object injected into the ObjectContentManager (see the interface org.apache.jackrabbit.ocm.mapper.Mapper). Right now, there are 2 different Mapping Descriptor implementations:

  • Annotation : each persistent object is annoted in order to provide to the ObjectContentManager all the required information on its mapping strategy (see the class org.apache.jackrabbit.ocm.mapper.impl.annotation.AnnotationMapperImpl).
  • XML configuration file : the class descriptors are defined in one or more XML config files used by the ObjectContentManager when it is instantiated (see the class org.apache.jackrabbit.ocm.mapper.impl.digester.DigesterMapperImpl).

For a business developer, it is not necessary to know how the ObjectContentManager is using the Class Descriptors. He has to make only a choice between annotated classes or XML files. Below, you can see how to setup correctly an ObjectContentManager.

How does an object is persisted into a JCR repository ?

In all cases, a persistent object (a pojo) is mapped into a JCR node and its fields are mapped into subnodes or properties depending on their types.

There are 3 “field types”:

  • Atomic fields
    Primitive data types and simple objects (String, Long, Double, …) . Those fields are mapped into JCR properties.

  • Bean fields
    One class can contain an 1..1 association to another bean. In this case, the field is a custom object. Those fields are mapped into JCR subnodes or a referenced node.

  • Collection fields
    One class can contain an 1..n association to a collection of beans (or Map). Those fields are mapped into a collection of JCR subnodes or a collection of referenced nodes. It is also possible to map a java collection into a multivalue property.

The Mapping descriptor contains also information on inheritances, interface mapping strategy, lazy loading, custom converter, cache strategy, etc.

Basic setup (with annotated persistent classes)

When you start your application, you need the following code to initialize correctly the Object Content Manager.

import javax.jcr.Session;
import javax.jcr.Repository;

import org.apache.jackrabbit.ocm.manager.impl.ObjectContentManagerImpl;
import org.apache.jackrabbit.ocm.mapper.Mapper;
import org.apache.jackrabbit.ocm.mapper.impl.annotation.AnnotationMapperImpl;


// 1. Instantiate a JCR session
Repository repository = ...;
Session session = repository.login(...);

// 2. Register the different persistent classes
List classes = new ArrayList();
classes.add(MyContent.class); // Call this method for each persistent class


// 3. Instantiate the object content manager
Mapper mapper = new AnnotationMapperImpl(classes);
ObjectContentManager ocm = new ObjectContentManagerImpl(session, mapper);

Basic setup (with one or more XML Mapping Descriptor files)

When you start your application, you need the following code to initialize correctly the Object Content Manager.

import javax.jcr.Session;
import javax.jcr.Repository;

import org.apache.jackrabbit.ocm.mapper.Mapper;
import org.apache.jackrabbit.ocm.mapper.impl.digester.DigesterMapperImpl;
import org.apache.jackrabbit.ocm.manager.ObjectContentManager;
import org.apache.jackrabbit.ocm.manager.impl.ObjectContentManagerImpl;
import org.apache.jackrabbit.ocm.manager.atomictypeconverter.AtomicTypeConverterProvider;
import org.apache.jackrabbit.ocm.manager.atomictypeconverter.impl.DefaultAtomicTypeConverterProvider;
import org.apache.jackrabbit.ocm.manager.objectconverter.ObjectConverter;
import org.apache.jackrabbit.ocm.manager.objectconverter.impl.ObjectConverterImpl;
import org.apache.jackrabbit.ocm.query.QueryManager;
import org.apache.jackrabbit.ocm.query.impl.QueryManagerImpl;

// 1. Instantiate a JCR session
Repository repository = ...;
Session session = repository.login(...);

// 2. Specify the different mapping files
String[] files = {
      "./src/test-config/jcrmapping.xml",
      "./src/test-config/jcrmapping-atomic.xml",
      "./src/test-config/jcrmapping-beandescriptor.xml"
  };

// 3. Instantiate the object content manager
ObjectContentManager ocm = new ObjectContentManagerImpl(session, files);

API Overview

With the current Object Manager API, it is possible to:

We plan to add other features in a future release.