I am getting the following error response from the server.
HTTP Status 500 –
type Exception report
message
descriptionThe server encountered an internal error () that prevented
it from fulfilling this request.exception
javax.servlet.ServletException:
java.lang.UnsupportedOperationException: Attempted to serialize
java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to
register a type adapter?root cause
java.lang.UnsupportedOperationException: Attempted to serialize
java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to
register a type adapter?
From Java debugger:
org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer@7632012e
I am using Gson to convert my Java objects to JSON. Below I have pasted some of my code.
This is my resource:
@Stateless
@LocalBean
@Path("/autos")
@Produces(MediaType.APPLICATION_JSON)
public class AutoResource {
@EJB
private CarAssembler warehouse;
@Context
private UriInfo uriInfo;
@GET
public Response allAutos() {
// Building a context, lots of code...
// Creating a Gson instance and configures it...
final Auto auto = warehouse.list(context);
final String autoJson = gson.toJson(auto);
return Response.ok(autoJson).build();
}
}
The CarAssembler is just an service which invokes a repository. I have not pasted the code of the service here.
Repository:
@Override
public Question findById(final int id, final FetchType fetchType) {
final Auto question = getEntityManager().find(Auto.class, id);
if (fetchType == FetchType.LAZY) {
return auto;
}
Hibernate.initialize(auto.getManufacturer());
Hibernate.initialize(auto.getAssemblyHouse());
return auto;
}
As you see, I provide both lazy and eager loading of objects. I use Hibernate.initialize to eager fetch JPA associations. However, the question is how I can fix the proxy error I am getting. Why come there is only AssemblyHouse that is still attached to JavaAssist, while Manufacturer is not (I have seen the type in Java Debugger). How do I know when to unproxy objects? Should I unproxy all associations this auto may have? And in which layer of my code? Does it affect the performance of my application when I unproxy? Are there other solutions? I see from the error message that I can make a type adapter. Yes, I could but then I have to do that for all domain objects to be sure that conversion is done correctly. Maybe other objects in my domain starts failing when I try to convert it into JSON representation too, but I don't know when or why. Is it just luck that the other objects are fine?
This is the way I am unproxing objects, but I have not implemented it yet, because I don't know if this is good or bad, and in what layer to do this, and when I should do it. Should I unproxy objects all the time?
public class HibernateUtilities {
public static <T> T unproxy(T proxy) {
if (proxy == null) {
return null;
}
if (proxy instanceof HibernateProxy) {
Hibernate.initialize(proxy);
HibernateProxy hibernateProxy = (HibernateProxy) proxy;
T unproxiedObject = (T) hibernateProxy.getHibernateLazyInitializer().getImplementation();
return unproxiedObject;
}
return proxy;
}
}
Stacktrace as requested:
[#|2012-11-22T17:17:13.285+0100|WARNING|glassfish3.1.2|javax.enterprise.system.container.web.com.sun.enterprise.web|_ThreadID=71;_ThreadName=Thread-8;|StandardWrapperValve[javax.ws.rs.core.Application]: PWC1406: Servlet.service() for servlet javax.ws.rs.core.Application threw exception java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: org.hibernate.proxy.HibernateProxy. Forgot to register a type adapter? at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:64) at com.google.gson.internal.bind.TypeAdapters$1.write(TypeAdapters.java:61) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.ArrayTypeAdapter.write(ArrayTypeAdapter.java:93) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195) at com.google.gson.Gson.toJson(Gson.java:586) at com.google.gson.Gson.toJson(Gson.java:565) at com.google.gson.Gson.toJson(Gson.java:520) at com.myapp.AutoResource.produceAuto(AutoResource.java:48) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1052) at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1124) at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:5388) at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:619) at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800) at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:571) at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doAround(SystemInterceptorProxy.java:162) at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:144) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:861) at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:800) at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:370) at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:5360) at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:5348) at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:214) at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:89) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205) at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:288) at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1469) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1400) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339) at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708) at javax.servlet.http.HttpServlet.service(HttpServlet.java:770) at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281) at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:175) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595) at org.apache.catalina.core.StandardHostValve.__invoke(StandardHostValve.java:161) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java) at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231) at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317) at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195) at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860) at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757) at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056) at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229) at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90) at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79) at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54) at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59) at com.sun.grizzly.ContextTask.run(ContextTask.java:71) at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532) at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513) at java.lang.Thread.run(Thread.java:722) |#]
Best Answer
You can do without manually unproxying everything by using a custom
TypeAdapter
. Something along these lines:To use it you must first register it:
Notice that this will recursively initialize every proxy you have in the object hierarchy; since however you have to serialize the whole data, you should have done that anyway.
How does this work?
GSON contains a number of
TypeAdapterFactory
implementations, for various types (primitive types, common types likeString
orDate
, lists, arrays...). Each factory is asked if it is able to serialize a certain Java type (the parameter tocreate
is aTypeToken
instead of aClass
in order to capture possible information about generic types, whichClass
does not have). If the factory is able to serialize/deserialize a type, it responds with aTypeAdapter
instance; otherwise it responds withnull
.HibernateProxyTypeAdapter.FACTORY
verifies whether type implementsHibernateProxy
; in that case, it returns an instance ofHibernateProxyTypeAdapter
for serialization. Thewrite
method is called when an actual object has to be serialized; the adapter extracts the original type of the underlying object, and asks GSON for the standardTypeAdapter
for the original type, which generally is aReflectiveTypeAdapter
.Then it retrieves an instance of the original class, instead of directly using the proxy. This is necessary because
ReflectiveTypeAdapter
accesses directly to fields, instead of using getters; accessing to the fields of a proxied object does not work, and is a classical Hibernate pitfall.As a possible performance improvement, the delegate
TypeAdapter
should be acquired in thecreate
method. I found out that callinggetSuperclass()
on the proxyClass
appears to yield the original base class. The code can then become: