spring-projects/spring-framework · error · IllegalArgumentException

Property 'target' is required

Error message

Property 'target' is required

What it means

Thrown by AbstractSingletonProxyFactoryBean.afterPropertiesSet when the 'target' property was never set on the FactoryBean. This class is the base of TransactionProxyFactoryBean, AsyncAnnotationBeanPostProcessor helpers, RmiProxyFactoryBean-style beans, etc., and the target object to be proxied is mandatory. Spring validates required properties before attempting proxy construction to fail fast with a clear message rather than an obscure NullPointerException later.

Source

Thrown at spring-aop/src/main/java/org/springframework/aop/framework/AbstractSingletonProxyFactoryBean.java:138

	 * containing BeanFactory for loading all bean classes. This can be
	 * overridden here for specific proxies.
	 */
	public void setProxyClassLoader(ClassLoader classLoader) {
		this.proxyClassLoader = classLoader;
	}

	@Override
	public void setBeanClassLoader(ClassLoader classLoader) {
		if (this.proxyClassLoader == null) {
			this.proxyClassLoader = classLoader;
		}
	}


	@Override
	public void afterPropertiesSet() {
		if (this.target == null) {
			throw new IllegalArgumentException("Property 'target' is required");
		}
		if (this.target instanceof String) {
			throw new IllegalArgumentException("'target' needs to be a bean reference, not a bean name as value");
		}
		if (this.proxyClassLoader == null) {
			this.proxyClassLoader = ClassUtils.getDefaultClassLoader();
		}

		ProxyFactory proxyFactory = new ProxyFactory();

		if (this.preInterceptors != null) {
			for (Object interceptor : this.preInterceptors) {
				proxyFactory.addAdvisor(this.advisorAdapterRegistry.wrap(interceptor));
			}
		}

		// Add the main interceptor (typically an Advisor).
		proxyFactory.addAdvisor(this.advisorAdapterRegistry.wrap(createMainInterceptor()));

View on GitHub (pinned to e8729d0438)

Solutions

1. Add the required target property pointing at the bean to be proxied, e.g. <property name="target" ref="myServiceBean"/>.
2. If configuring programmatically, call factoryBean.setTarget(theTargetInstance) before the container initializes it (or before manually calling afterPropertiesSet).
3. Double-check the target is a real bean reference (ref=), not a string literal (value=), which triggers error 63 instead.
4. For FactoryBean subclasses, ensure the subclass's createMainInterceptor() also resolves correctly since target validation runs first.

Example fix

// before
<bean id="txProxy" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">
  <property name="transactionManager" ref="tm"/>
  <!-- target missing -->
</bean>

// after
<bean id="txProxy" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">
  <property name="transactionManager" ref="tm"/>
  <property name="target" ref="myService"/>
</bean>

// Before letting the container initialize the FactoryBean:
AbstractSingletonProxyFactoryBean fb = ...; // e.g. TransactionProxyFactoryBean
if (fb.getTarget() == null) {  // note: target is private; use the public accessor or assertion on your wiring
  throw new IllegalStateException("target not set on " + fb.getClass().getSimpleName());
}
// In practice, enforce this via your config layer / a BeanPostProcessor check.

When it happens

Trigger: Declaring a bean that subclasses AbstractSingletonProxyFactoryBean (e.g. TransactionProxyFactoryBean) in XML/Java config without a <property name="target" ref="..."/> or setTarget(...) call. Also when programmatic config forgets to call setTarget before afterPropertiesSet is invoked by the container.

Common situations: Removing the target property during refactoring; copy-pasting a FactoryBean definition and dropping the target line; accidentally wiring target as a value rather than ref so it ends up null; initializing the bean manually without calling afterPropertiesSet.

Related errors

• MethodInvocation is not a Spring ProxyMethodInvocation: {}
• [{}] is not an interface
• Could not generate CGLIB subclass of {advised.getTargetClass
• Not running in a ConfigurableBeanFactory: {beanFactory}
• 'argumentNames' property of AbstractAspectJAdvice contains a

AI-assisted analysis of spring-projects/spring-framework@e8729d0438 (2026-08-04). Data as JSON: /data/errors/6784f9c9a8b7b5e8.json. Report an issue: GitHub.