Linkage Error: Loader Constraint Violation when using CXF with Jetty 6 Plus

To keep this post as short as possible, a detail description of the problem can be found in here and here. What actually happens in my case is that when I reload the web service application in a container, this linkage error occurs. The loader constraint is violated because it happens that two classloaders (the current class loader and the superclass loader) have different class objects for the type javax.activation.DataHandler used in the signature.

There are different ways to fix this problem. For example, unjar geronimo-activation_1.1_spec-1.0.2.jar and remove the associated classes from it. However, this is very intrusive. Another approach is to instruct Jetty to allow the normal java behavior to be used and all classes will be loaded from the system classpath if possible. This can be done by setting the webAppContext's parentLoaderPriority to true in jetty-web.xml. This is fine however it affects all classes behaviors since every class will be loaded from the system classpath if found. A better approach (I think) is to control the class loading behavior in a per class basis. This can be done by setting the webAppContext's systemClasses property to include javax.activation. in the list of classes that cannot be overridden by webapp context classloaders.

A sample of the jetty-web.xml is as follows:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">

<Configure class="org.mortbay.jetty.webapp.WebAppContext">

<!-- this is needed to avoid LinkageError: loader constraint violation -->

<Set name="systemClasses">

<Array type="String">

<Item>java.</Item>

<Item>javax.servlet.</Item>

<Item>javax.xml.</Item>

<Item>org.mortbay.</Item>

<Item>org.xml.</Item>

<Item>org.w3c.</Item>

<Item>org.apache.commons.logging.</Item>

<Item>org.apache.log4j.</Item>

<Item>javax.activation.</Item>

</Array>

</Set>

</Configure>

Hope this is helpful to someone else as well. :)

CXF Development Notes

These days, I'm prototyping SOAP web services using CXF. It is a nice framework with spring built-in support. Basically, I can now design, develop and test the web service within eclipse with the help of the WTP plugin (beta).

Here is what I did:

1. Start with a pojo; define the methods that will be exposed to the web
2. Generate getters and setters for the pojo
3. Use the WTP plugin to develop the service following the tutorial described here.
4. Write unit test for the web service

Sound simple, isn't it? However, you will encounter at least 2 problems:

Problem 1:

The pojo has annotations that are not part of the CXF annotations. When I use WTP plugin to generate the web service, the generated web service is usable. The exact cause of the problem is not known yet (not that important for now as I'm prototyping it). The workaround is to remove those unrecognized annotations before going to Step 3.

Problem 2:

Since one of my private members in the pojo represents an interface of a class, the CXF complaints:

javax.xml.ws.WebServiceException: org.apache.cxf.service.factory.ServiceConstructionException

at org.apache.cxf.jaxws.EndpointImpl.doPublish(EndpointImpl.java:275)

at org.apache.cxf.jaxws.EndpointImpl.publish(EndpointImpl.java:209)

at org.apache.cxf.jaxws.spi.ProviderImpl.createAndPublishEndpoint(ProviderImpl.java:84)

at javax.xml.ws.Endpoint.publish(Unknown Source)

at com.boci.sample.test.MarketData_PortTypeTest.setupServer(MarketData_PortTypeTest.java:58)

at com.boci.sample.test.MarketData_PortTypeTest.startServices(MarketData_PortTypeTest.java:43)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)

at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)

at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)

at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:27)

at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)

at org.junit.runners.ParentRunner.run(ParentRunner.java:220)

at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46)

at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)

at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Caused by: org.apache.cxf.service.factory.ServiceConstructionException

at org.apache.cxf.jaxb.JAXBDataBinding.initialize(JAXBDataBinding.java:354)

at org.apache.cxf.service.factory.ReflectionServiceFactoryBean.buildServiceFromClass(ReflectionServiceFactoryBean.java:381)

at org.apache.cxf.jaxws.support.JaxWsServiceFactoryBean.buildServiceFromClass(JaxWsServiceFactoryBean.java:523)

at org.apache.cxf.service.factory.ReflectionServiceFactoryBean.initializeServiceModel(ReflectionServiceFactoryBean.java:444)

at org.apache.cxf.service.factory.ReflectionServiceFactoryBean.create(ReflectionServiceFactoryBean.java:195)

at org.apache.cxf.jaxws.support.JaxWsServiceFactoryBean.create(JaxWsServiceFactoryBean.java:163)

at org.apache.cxf.frontend.AbstractWSDLBasedEndpointFactory.createEndpoint(AbstractWSDLBasedEndpointFactory.java:100)

at org.apache.cxf.frontend.ServerFactoryBean.create(ServerFactoryBean.java:117)

at org.apache.cxf.jaxws.JaxWsServerFactoryBean.create(JaxWsServerFactoryBean.java:167)

at org.apache.cxf.jaxws.EndpointImpl.getServer(EndpointImpl.java:346)

at org.apache.cxf.jaxws.EndpointImpl.doPublish(EndpointImpl.java:259)

... 21 more

Caused by: com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions

org.openspaces.core.GigaSpace is an interface, and JAXB can't handle interfaces.

this problem is related to the following location:

at org.openspaces.core.GigaSpace

at private org.openspaces.core.GigaSpace com.boci.sample.jaxws_asm.SetGigaSpace.arg0

at com.boci.sample.jaxws_asm.SetGigaSpace

org.openspaces.core.GigaSpace does not have a no-arg default constructor.

this problem is related to the following location:

at org.openspaces.core.GigaSpace

at private org.openspaces.core.GigaSpace com.boci.sample.jaxws_asm.SetGigaSpace.arg0

at com.boci.sample.jaxws_asm.SetGigaSpace

at com.sun.xml.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:102)

at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:472)

at com.sun.xml.bind.v2.runtime.JAXBContextImpl.(JAXBContextImpl.java:302)

at com.sun.xml.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1136)

at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:154)

at com.sun.xml.bind.v2.ContextFactory.createContext(ContextFactory.java:121)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at javax.xml.bind.ContextFinder.newInstance(Unknown Source)

at javax.xml.bind.ContextFinder.find(Unknown Source)

at javax.xml.bind.JAXBContext.newInstance(Unknown Source)

at org.apache.cxf.jaxb.JAXBDataBinding.createJAXBContextAndSchemas(JAXBDataBinding.java:500)

at org.apache.cxf.jaxb.JAXBDataBinding.initialize(JAXBDataBinding.java:337)

... 31 more

This sounds horrible but it can be fixed by annotating the getters and the setters with the @webmethod(exclude=true). and voila, everything should work :)

Hopefully, this trick will be helpful for someone else as well.