Spring 解决循环依赖

在编写Spring 时，会遇到循环依赖的问题，如下：

	
	<bean id="cycleA" class="di.cycledependency.CycleDependencyA">
		<constructor-arg ref="cycleB"/>
	</bean>
	<bean id="cycleB" class="di.cycledependency.CycleDependencyB">
		<constructor-arg ref="cycleA"/>
	</bean>

 

public class CycleDependencyA {
	private final CycleDependencyB b;
	public CycleDependencyA(CycleDependencyB b) {
		this.b = b;
	}
}

public class CycleDependencyB {
	private final CycleDependencyA a;

	public CycleDependencyB(CycleDependencyA a) {
		this.a = a;
	}
	
}

 

 

Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'cycleA': Requested bean is currently in creation: Is there an unresolvable circular reference?
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:339)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:215)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
	... 29 more

 解决方法是用Setter代替构造函数：

package di.cycledependency;

public class CycleDependencyA {
	private CycleDependencyB b;

	public void setB(CycleDependencyB b) {
		this.b = b;
	}
	
}

package di.cycledependency;

public class CycleDependencyB {
	private CycleDependencyA a;

	public void setA(CycleDependencyA a) {
		this.a = a;
	}

	
}

 

	<bean id="cycleA" class="di.cycledependency.CycleDependencyA">
		<property name="b" ref="cycleB"/>
	</bean>
	<bean id="cycleB" class="di.cycledependency.CycleDependencyB">
		<property name="a" ref="cycleA"/>
	</bean>