NullPointerException in Marshalling.fromJSON(Marshalling.java:157)

[froed]

Hi all,

I'm using the current SNAPSHOT of the errai JAXRS and I get the following exception:

13:56:39.286 [ERROR] [App] Uncaught exception escaped
java.lang.NullPointerException: null
    at org.jboss.errai.marshalling.client.Marshalling.fromJSON(Marshalling.java:157)
    at org.jboss.errai.enterprise.client.jaxrs.MarshallingWrapper.fromJSON(MarshallingWrapper.java:56)
    at org.jboss.errai.enterprise.client.jaxrs.JaxrsProxyLoaderImpl$1ISupplierServiceRemoteImpl$1.onResponseReceived(JaxrsProxyLoaderImpl.java:587)
    at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:287)
    at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:395)
    at sun.reflect.GeneratedMethodAccessor41.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:213)
    at sun.reflect.GeneratedMethodAccessor39.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:292)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Thread.java:722)

it's in

public static <T> T fromJSON(String json, Class<T> type, Class<?> assumedElementType) {
    EJValue parsedValue = ParserFactory.get().parse(json);
    MarshallingSession session = MarshallingSessionProviderFactory.getDecoding();
    if (assumedElementType != null) {
      session.setAssumedElementType(assumedElementType.getName());
    }
    Marshaller<Object> marshallerInstance = session.getMarshallerInstance(type.getName());
    return (T) marshallerInstance.demarshall(parsedValue, session);
  }

the marshallerInstance becomes null

I can't debug into the MarshallerFactoryImpl class but it is generate inside the .errai folder as well as the JaxrsProxyLoaderImpl class

what could be the problem?

[csa]

Hi Dave,

That's strange. Errai couldn't find a statically generated marshaller for the type passed to session.getMarshallerInstance(). Can you break at MarshallingWrapper.java:56 and see which type that it tries to demarshall?

There should be a marshaller for that type in the generated MarshallerFactoryImpl.

Cheers,

Christian

[froed]

I've found the problem.

this is my original interface

@Path("/supplier")
public interface ISupplierServiceRemote {
    @GET
    @Path("/list")
    @Produces("application/json")
    public Collection<Supplier> list();

    @GET
    @Path("/{supplierName}/productionUnit/list")
    @Produces("application/json")
    public Collection<ProductionUnit> listProductionUnit(@PathParam("supplierName") String supplierName);

    @GET
    @Path("/{supplierName}/productionUnit/{productionUnitName}/products/list")
    @Produces("application/json")
    public Collection<ProductProductionUnit> listProducts(@PathParam("supplierName") String supplierName, @PathParam("productionUnitName") String productionUnitName);
}

It shows that it returns a Collection. After changing it to List the error is gone.

for example:

public List<Supplier> list();

Is it possible to FIX this. Since I don't want to change already existing interfaces from a Collection to List.

[csa]

Yeah the problem here is that we wouldn't know if Collection should be marshalled as a List or Set etc. You can configure an alias in ErraiApp.properties though: https://docs.jboss.org/author/display/ERRAI/Marshalling#Marshalling-AliasedMappingsofExistingInterfaceContracts

errai.marshalling.mappingAliases=java.util.ArrayList->java.util.Collection

[froed]

Hi Christian,

I tried out your solution, but it didn't help to solve the problem.

I put the line you suggested into my client as well as in the project with the REST interface. The marshallerInstance is still null. In the MarshallingWrapper in

public static <T> T fromJSON(String json, Class<T> type, Class<?> elementType) {
    return Marshalling.fromJSON(_fromJSON(json), type, elementType);
  }

the type is java.util.Collection

[csa]

Hi Dave,

I just pushed a test that confirms this functionality. However, in the example above I had the ordering wrong. It should be:

errai.marshalling.mappingAliases=java.util.Collection->java.util.ArrayList

Also make sure to delete your .errai directory (contains the generated and cached marshallers) so that the marshallers get re-generated.

Cheers,

Christian

[froed]

Hi Christian,

that was the trick, thank you for the response.

Great work with the JAX-RS and CDI in the errai framework, it simplifies the work for the communication with the server part, which was always a drawback in GWT in comparison i.e. to vaadin.