CGLIB Proxy, no default constructor

Hi,

I'm trying to proxy a concrete class (com.company.Concrete) which only as a one-argument constructor.

ApplicationContext

Code:

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        <aop:aspectj-autoproxy proxy-target-class="true" />
        <bean id="concrete" class="com.company.Concrete" scope="prototype" />

---

Initialization code (try 1):

Code:

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        Object args = ...
        // throws exception
        Concrete c = (Concrete) applicationContext.getBean("concrete", args);

---

Initialization code (try 2):

Code:

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      Object args = ...
      // Also throws exception
      Concrete concrete = (Concrete) applicationContext.getAutowireCapableBeanFactory().initializeBean(
            new Concrete(args), "concrete");

---

Exception

Code:

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rg.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class com.company.Concrete]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Superclass has no null constructors but no arguments were given
        at org.springframework.aop.framework.Cglib2AopProxy.getProxy(Cglib2AopProxy.java:212)
        at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:112)
        at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.createProxy(AbstractAutoProxyCreator.java:476)
        at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.wrapIfNecessary(AbstractAutoProxyCreator.java:362)
        at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(AbstractAutoProxyCreator.java:322)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:407)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1418)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
        ... 10 more
Caused by: java.lang.IllegalArgumentException: Superclass has no null constructors but no arguments were given
        at net.sf.cglib.proxy.Enhancer.emitConstructors(Enhancer.java:721)
        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:216)
        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:200)
        ... 17 more

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I don't see why this should be a problem.
I'm using GenericApplicationContext which invokes getBean() with the necessary constructor arguments. Shouldn't spring delegate to the appropriate CGLIB method (which does take constructor arguments) ?


Note, I've also tried using a private default constructor with no success.



Regards,
Johan

It has nothing to do with spring. CGLib creates a subclass for class proxying and due to that it requires a no-argument constructor to be available.

Thanks for your reply. What about Enhancer.create(java.lang.Class[], java.lang.Object[]) ?

I'm having the same issue. I found code that uses that Enhancer method that Toxic mentions.

Cglib2AopProxy has a method

Code:

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public void setConstructorArguments(Object[] constructorArgs, Class[] constructorArgTypes)

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but it is not called anywhere in spring that I(ntelliJ) can find. If it were called, then it seems like Spring could handle objects without no-arg constructors since there's this, in the same class:

Code:

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public Object getProxy(ClassLoader classLoader) {
{snip}


// Generate the proxy class and create a proxy instance.
    Object proxy;
    if (this.constructorArgs != null) {
        proxy = enhancer.create(this.constructorArgTypes, this.constructorArgs);
    }
    else {
        proxy = enhancer.create();
    }

    return proxy;
}

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This is using Spring 3.0.6 with cglib 2.2.2.