Question

// Two third-party factories:

public class OneStaticMethodFactory {
 ...
 public static Object createFactory(String oneInstanceMethodFactoryClassName) {
  ...
 }
}

public class OneInstanceMethodFactory {
 ...
 public OneObject createObject() {
  ...
 }
}

// Hardwired code:

OneInstanceMethodFactory oneInstanceMethodFactory = 
 (OneInstanceMethodFactory) 
  OneStaticMethodFactory.createFactory("pkg.to.OneInstanceMethodFactory");

OneObject oneObject =
 oneInstanceMethodFactory.createObject(); 

// Attempt to replace them by Spring beans:

<bean id="oneInstanceMethodFactory" class="pkg.to.OneStaticMethodFactory"
 factory-method="createFactory">
  <constructor-arg value="pkg.to.OneInstanceMethodFactory">
  </constructor-arg>
</bean>

<bean id="oneObject" factory-bean="oneInstanceMethodFactory"
 factory-method="createObject">
</bean>

// Run Spring IoC:

java.lang.IllegalStateException: Failed to load ApplicationContext
    ...
Caused by: org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 'oneObject' defined in class path resource [applicationContext.xml]: 
No matching factory method found: factory bean 'oneInstanceMethodFactory'; 
factory method 'createObject()'. 
Check that a method with the specified name and arguments exists and that it is non-static.
        at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:528)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1015)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:911)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:485)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:605)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:925)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:472)
        at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:103)
        at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:1)
        at org.springframework.test.context.support.DelegatingSmartContextLoader.loadContext(DelegatingSmartContextLoader.java:228)
        at org.springframework.test.context.TestContext.loadApplicationContext(TestContext.java:124)
        at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:148)
        ... 26 more

To solve the problem above, how to downcast oneInstanceMethodFactory bean from compile-time type Object to runtime type OneInstanceMethodFactory in Spring? (Modification of the two third-party factory classes would not be the point on question.)

@EDIT

Thanks to the hints from @Boris Treukhov, finally i figured out that the problem had nothing to do with type downcast but indeed OneStaticMethodFactory#createFactory returned other runtime type than OneInstanceMethodFactory due to a typo myself. Now everything works as expected after the migration from the hardwired code to Spring IoC / DI above.

Answer 1

You should check that 'oneInstanceMethodFactory', is really a OneInstanceMethodFactory instance, either by checking what bean type was created with name "oneInstanceMethodFactory" through the container’s getBean() method or by examining the value returned by createFactory in the debugger.

In my experience this exception is very straightforward, usually there’s really no such a public non-static method.

Downcasting makes no difference because the methods are called through the reflection method which takes an Object instance as this argument. The bean type is determined by the value returned from the factory method, Spring don’t need to know the class before the bean is initialized. In fact oneObject bean depends on oneInstanceMethodFactory so the latter bean will be fully initialized before the former, and the Spring will be able to call its createObject method.