Jbx4j - JSON Binding eXtension for JPA

A helper library for JPA Entity (de)serialization in JSON.

When we work with JPA and need to (de)serialize JPA entities to JSON (or any other format) we always encounter some problems:

• Relationship attributes (OneToOne, ManyToOne, OneToMany and ManyToMany) that are Lazy and the JSON Binding framework (like Jackson, GSON, etc) will cause the JPA Provider to make unnecessary queries to the database;
• Circular reference between JPA mapping;
• Use of DTOs and Mapping frameworks (like ModelMapper, MapStruct, Dozer, etc.) to bypass the above problems, making development more complex and verbose;
• Need to create DTOs and Mappers even for simple entities (with two or three attributes).

This library helps in the process of (de)serialization of the JPA entity, reducing the difficulties mentioned above.

Support

Initially we are providing support to the framework below:

Framework	Type	Minimal version	Note
Hibernate	JPA	5.2
EclipseLink	JPA	2.5	Works only with Weaving enabled. Experimental support
Jackson	JSON	2.9.4

Getting Started

1. You must add a dependency in your project:

   <dependency>
       <groupId>com.github.microtweak</groupId>
       <artifactId>jbx4j-hibernate</artifactId>
       <version>${jbx4j.version}</version>
   </dependency>
   
   <dependency>
       <groupId>com.github.microtweak</groupId>
       <artifactId>jbx4j-jackson</artifactId>
       <version>${jbx4j.version}</version>
   </dependency>

2. Now let's configure the application to use Jbx4j. Although the following examples are based on the CDI, it is not a requirement to use this library. Create a class that implements EntityResolver as in the example below. You can create multiple EntityResolvers as needed.

   @ApplicationScoped
   public class GenericEntityResolver implements EntityResolver<Object> {
   
       @Inject
       private EntityManager entityManager;
   
       @Override
       public boolean canResolve(Object declaredAt, Class<Object> rawType, JpaEntityData<Object> data, List<Annotation> annotations) {
           return rawType.isAnnotationPresent(Entity.class);
       }
   
       @Override
       public Object resolve(Object declaredAt, Class<Object> rawType, JpaEntityData<Object> data, List<Annotation> annotations) {
           Object primaryKey = data.get("id");
       
           if (primaryKey == null) {
               return null;
           }
       
           // Logic to solve the entity. You can use a find or a complex query JPQL
           return entityManager.find(rawType, primaryKey);
       }    
   
   }

3. Instantiate the Jbx4j module and add all the EntityResolvers created in the module. After that, register the module in Jackson.

   public class JacksonProducer {
   
       // Ask the CDI to find all the EntityResolver in the application
       @Inject
       private Instance<EntityResolver<?>> resolvers;
       
       @Produces
       @Singleton
       public ObjectMapper createJacksonObjectMapper() {
           ObjectMapper mapper = new ObjectMapper();
           
           // Instances the Jbx4j module for Jackson
           Jbx4jJacksonModule jbx4jModule = new Jbx4jJacksonModule();
   
           // Adds all EntityResolvers found by CDI in the module created earlier
           resolvers.forEach(er -> jbx4jModule.getResolverManager().add(er));
           
           // Register the module in Jackson
           mapper.registerModule(jpaJacksonModule);
           
           return mapper;
       }
       
   }

After these steps, simply ask Jackson's ObjectMapper to (de)serialize your JPA entity as you are already accustomed to doing with other Java classes.