LazyInitializationException when serializing Collection with Jackson

Question

I'm building an application using AngularJs and Rest services (RestEasy) where I need to display a list of products. Once the list is loaded when the user clicks on one of the products, the details and images of this product are loaded.

I don't want to load the collections associated to the products (i.e Images) when I display the list of all products but only when I need the details of one of them, for performance reasons, so I'm using Lazy load.

Hibernate is doing fine and I can see that initially I only load some of the atributes but not the collections, however in the rest service, when Jackson tries to access the collection to serialize it, I'm getting this famous exception:

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.domainmodel.Product.Images

Of course at that moment there is no longer Session opened and the database transaction has been commited. I don't want to keep the session opened. So searching on the net I saw that we can tell Jackson not to serialize a property using the annotation @JsonIgnore. This annotation has to be placed in the property or getter of the Entity (POJO), so basically, if I tell Jackson not to serialize this collection when serializing to JSON, it will solve the problem temporarily but once I need to load the product with the collection because the user has clicked on it, it won't serialize the collection so I will have this problem later. So I don't think this is a solution for me. Any ideas, advices on how to solve this situation?? I post the code of the entity and the rest service here. Thank you in advance!!

@Entity
@Table(name = "PRODUCTS")
public class Product implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "ID")
private Long id;

@Column(name = "PATH_TO_IMAGE", nullable = false, insertable = true, updatable = true)
private String pathToImage;

@Column(name="DESCRIPTION",nullable=true, insertable = true, updatable = true)
private String description;

@ManyToOne(optional = false)
@JoinColumn(name = "XID_PRODUCT_TYPE", nullable = false, insertable = false, updatable = false)
private ProductType productType;


@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(
        name = "PRODUCT_IMAGE",
        joinColumns = {@JoinColumn(name = "XID_PRODUCT", referencedColumnName = "ID")},
        inverseJoinColumns = {@JoinColumn(name = "XID_IMAGE", referencedColumnName = "ID")})
private List<Image> images;

... getters and setters 
}

And then the code of the rest service:

@Path("/products")
public class ProductsService extends CommonService{

private static final Logger log =  Logger.getLogger(ProductsService.class);


@EJB
private ProductsServiceHandler handler;

@GET
@Produces(MediaType.APPLICATION_JSON)
public Response getAllProducts(@Context Request request, @Context HttpHeaders httpHeaders)
{
    try
    {
        List<Product> products=handler.findAllProducts();
        return Response.ok(products).header(ALLOW_ORIGIN_HEADER, "*").build();
    }
    catch(Exception e){return Response.status(Status.INTERNAL_SERVER_ERROR).build();}
}

}

The complete stackstrace as requested:

 2015-02-03 00:35:41,085 ERROR [io.undertow.request] (default task-9) UT005023: Exception handling request to /arenaclub/rest/products: org.jboss.resteasy.spi.UnhandledException: Response is committed, can't handle exception
at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:148) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:432) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:376) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs-3.0.8.Final.jar:]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [jboss-servlet-api_3.1_spec-1.0.0.Final.jar:1.0.0.Final]
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:61) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:113) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:56) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:45) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:61) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:70) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:240) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:227) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:73) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:146) [undertow-servlet-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:177) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:727) [undertow-core-1.0.15.Final.jar:1.0.15.Final]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [rt.jar:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [rt.jar:1.8.0_25]
at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_25]
Caused by: com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.fgonzalez.domainmodel.Product.images, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.fgonzalez.domainmodel.Product["images"])
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:232) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:197) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:187) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:652) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:152) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:100) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:21) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:183) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:114) [jackson-databind-2.3.2.jar:2.3.2]
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:610) [jackson-databind-2.3.2.jar:2.3.2]
at org.jboss.resteasy.plugins.providers.jackson.ResteasyJackson2Provider.writeTo(ResteasyJackson2Provider.java:186) [resteasy-jackson2-provider-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.writeTo(AbstractWriterInterceptorContext.java:129) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.ServerWriterInterceptorContext.writeTo(ServerWriterInterceptorContext.java:62) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:118) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.security.doseta.DigitalSigningInterceptor.aroundWriteTo(DigitalSigningInterceptor.java:143) [resteasy-crypto-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:122) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.plugins.interceptors.encoding.GZIPEncodingInterceptor.aroundWriteTo(GZIPEncodingInterceptor.java:100) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:122) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.ServerResponseWriter.writeNomapResponse(ServerResponseWriter.java:99) [resteasy-jaxrs-3.0.8.Final.jar:]
at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:427) [resteasy-jaxrs-3.0.8.Final.jar:]
... 32 more

Answer 1

The folks over at the Jackson project developed a nice module to solve this problem!

Check it out on github at: https://github.com/FasterXML/jackson-datatype-hibernate

Answer 2

You can consider two possible options:

1. Use separate Data Transfer Objects (DTOs) for your Service Layer, so you will manage getting required information during Entity -> DTO conversion. The disadvantage of this approach - you need to write and maintain these converters. On other hand you have full flexibility of combining any entities into your Service Response. Preferred option.
2. Create separate lightweight Entity (e.g. "ProductInfo") to be used for "products" call. There shouldn't be any issues with mapping several Entities to one DB table.

Answer 3

There are a couple of things you could do.

1. The quickest way - loop through products and call setImages(null) on each product prior to returning the result
2. Register two custom JSON serializers for Product, one which would serialize images and one which wouldn't, and choose the serializer based on service which is called. The problem is I'm not sure this can be done with RestEasy, but take a look at this thread for some hints
3. Don't return your entity beans from REST service, use DTOs instead so you can easily control what you return and in what format. Another big plus is that you decouple the REST layer from entity beans which gives you freedom to change entities without worrying about changing the format which REST users expect. This would be the preferred option.

Answer 4

You could run Jackson inside a JPA session, so lazy loading will work.