Creating mixin fails if target has no default constructor

[swisswheel]

Hello,

Is it true that the target object of a mixin has to have a default constructor? I'm using cglib 2.1_2 and spring 1.2.1. I've got following code to create a mixin:

            Exception e = ...
            String stackTrace = ...
            ProxyFactory factory = new ProxyFactory();
            factory.setProxyTargetClass(true); // Enforce CGLIB usage
            factory.setTarget(e); // Exception which has to be wrapped

            MockControl stControl 
                = MockControl.createControl(ServerSideStackTrace.class);
            ServerSideStackTrace st 
                = (ServerSideStackTrace) stControl.getMock();
            st.getServiceSideStackTrace();
            stControl.setReturnValue(stackTrace, 0, Integer.MAX_VALUE);
            stControl.replay();

            factory.addAdvisor(0, new DefaultIntroductionAdvisor(
                new DelegatingIntroductionInterceptor(st), 
                ServerSideStackTrace.class));

            Exception wrappedException 
                = (Exception) factory.getProxy();
            
            stControl.verify();
            return wrappedException;

I've got the interface ServerSideStackTrace which has a method getServiceSideStackTrace to return a string. If the given exception e has a default constructor this code works. If not factory.getProxy() throws following exception:

java.lang.IllegalArgumentException: Superclass has no null constructors but no arguments were given
	at net.sf.cglib.proxy.Enhancer.emitConstructors(Enhancer.java:712)
	at net.sf.cglib.proxy.Enhancer.generateClass(Enhancer.java:499)
	at net.sf.cglib.transform.TransformingClassGenerator.generateClass(TransformingClassGenerator.java:33)
	at net.sf.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
	at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:215)
	at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377)
	at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:285)
	at org.springframework.aop.framework.Cglib2AopProxy.getProxy(Cglib2AopProxy.java:194)
	at org.springframework.aop.framework.Cglib2AopProxy.getProxy(Cglib2AopProxy.java:150)
	at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:67)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.DefaultHandler.enrichExceptionWithStackTrace(DefaultHandler.java:291)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.DefaultHandler.translateToBusinessException(DefaultHandler.java:196)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.SoapExceptionManager.translateToBusinessException(SoapExceptionManager.java:179)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.ClientSoapInvocationHandler.findAndTranslateAxisFault(ClientSoapInvocationHandler.java:96)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.ClientSoapInvocationHandler.findAndTranslateAxisFault(ClientSoapInvocationHandler.java:98)
	at ch.elca.leaf3.services.remoting.protocol.soap.axis.faulthandling.ClientSoapInvocationHandler.invoke(ClientSoapInvocationHandler.java:75)
	at $Proxy2.throwMeASpecialException(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at ch.elca.leaf3.services.remoting.ClientContextInvocationHandler.invoke(ClientContextInvocationHandler.java:126)
	at $Proxy3.throwMeASpecialException(Unknown Source)
	at ch.elca.leaf3.tests.remoting.CalculatorSoapTest.testSpecialExceptionBehaviour(CalculatorSoapTest.java:93)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:324)
	at junit.framework.TestCase.runTest(TestCase.java:154)
	at junit.framework.TestCase.runBare(TestCase.java:127)
	at junit.framework.TestResult$1.protect(TestResult.java:106)
	at junit.framework.TestResult.runProtected(TestResult.java:124)
	at junit.framework.TestResult.run(TestResult.java:109)
	at junit.framework.TestCase.run(TestCase.java:118)
	at junit.framework.TestSuite.runTest(TestSuite.java:208)
	at junit.framework.TestSuite.run(TestSuite.java:203)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:436)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:311)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

Does anybody see what I'm doing wrong?
Thanks for your help!

Cheers,
Martin

[katentim]

I think this is a limitation of CGLIB - see this JIRA entry.

You can try using interfaces + JDK dynamic proxy.