1. 概述
在本教程中，我们将讨论Spring org.springframework.beans.factory.BeanCreationException。当BeanFactory创建bean定义的bean并遇到问题时抛出一个非常常见的异常。本文将探讨此异常的最常见原因以及解决方案。
延伸阅读
Spring的控制反转和依赖注入简介
快速介绍控制反转和依赖注入的概念，然后使用Spring框架进行简单演示
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Spring中的BeanNameAware和BeanFactoryAware接口
查看在Spring中使用BeanNameAware和BeanFactoryAware接口。
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Spring 5函数Bean注册
查看如何使用Spring 5中的函数式方法注册bean。
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2. 原因：org.springframework.beans.factory.NoSuchBeanDefinitionException
到目前为止，BeanCreationException最常见的原因是Spring试图注入上下文中不存在的bean。
例如，BeanA试图注入BeanB：
@Component
public class BeanA {
@Autowired
private BeanB dependency;
// ...
}
如果在上下文中找不到BeanB，则会抛出以下异常(创建Bean时出错)：
Error creating bean with name 'beanA': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: private cn.tuyucheng.taketoday.web.BeanB cpm.baeldung.web.BeanA.dependency;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [cn.tuyucheng.taketoday.web.BeanB] found for dependency:
expected at least 1 bean which qualifies as autowire candidate for this dependency.
Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
要诊断此类问题，我们首先要确保已声明bean：
- 在XML配置文件中使用
元素 - 或通过@Bean注解在Java@Configuration类中
- 或者用@Component、@Repository、@Service、@Controller注解，并且类路径扫描对该包是活动的
我们还将检查Spring是否实际获取配置文件或类，并将它们加载到主上下文中。
3. 原因：org.springframework.beans.factory.NoUniqueBeanDefinitionException
bean创建异常的另一个类似原因是Spring尝试按类型(即按其接口)注入bean，并在上下文中找到两个或多个实现该接口的bean。
例如，BeanB1和BeanB2都实现了相同的接口：
@Component
public class BeanB1 implements IBeanB { ... }
@Component
public class BeanB2 implements IBeanB { ... }
@Component
public class BeanA {
@Autowired
private IBeanB dependency;
...
}
这将导致Spring bean工厂抛出以下异常：
Error creating bean with name 'beanA': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: private cn.tuyucheng.taketoday.web.IBeanB cn.tuyucheng.taketoday.web.BeanA.b;
nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException:
No qualifying bean of type [cn.tuyucheng.taketoday.web.IBeanB] is defined:
expected single matching bean but found 2: beanB1,beanB2
4. 原因：org.springframework.beans.BeanInstantiationException
4.1 自定义异常
接下来是一个在其创建过程中抛出异常的bean。一个易于理解问题的简化示例是在bean的构造函数中抛出异常：
@Component
public class BeanA {
public BeanA() {
super();
throw new NullPointerException();
}
// ...
}
正如预期的那样，这将导致Spring快速失败并出现以下异常：
Error creating bean with name 'beanA' defined in file [...BeanA.class]:
Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException:
Could not instantiate bean class [cn.tuyucheng.taketoday.web.BeanA]:
Constructor threw exception;
nested exception is java.lang.NullPointerException
4.2 java.lang.InstantiationException异常
BeanInstantiationException的另一种可能出现是将抽象类定义为XML中的bean；这必须在XML中，因为在Java@Configuration文件中无法做到这一点，类路径扫描将忽略抽象类：
@Component
public abstract class BeanA implements IBeanA { ... }
这是bean的XML定义：
<bean id="beanA" class="cn.tuyucheng.taketoday.web.BeanA" />
此设置将导致类似的异常：
org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'beanA' defined in class path resource [beansInXml.xml]:
Instantiation of bean failed;
nested exception is org.springframework.beans.BeanInstantiationException:
Could not instantiate bean class [cn.tuyucheng.taketoday.web.BeanA]:
Is it an abstract class?;
nested exception is java.lang.InstantiationException
4.3 java.lang.NoSuchMethodException异常
如果bean没有默认构造函数，而Spring试图通过查找该构造函数来实例化它，这将导致运行时异常：
@Component
public class BeanA implements IBeanA {
public BeanA(final String name) {
super();
System.out.println(name);
}
}
当类路径扫描机制拾取这个bean时，失败将是：
Error creating bean with name 'beanA' defined in file [...BeanA.class]: Instantiation of bean failed;
nested exception is org.springframework.beans.BeanInstantiationException:
Could not instantiate bean class [cn.tuyucheng.taketoday.web.BeanA]:
No default constructor found;
nested exception is java.lang.NoSuchMethodException: cn.tuyucheng.taketoday.web.BeanA.<init>()
当类路径上的Spring依赖项没有相同的版本时，可能会发生类似的异常，但更难诊断。由于API更改，这种版本不兼容可能会导致NoSuchMethodException。解决此类问题的方法是确保所有Spring库在项目中具有完全相同的版本。
5. 原因：org.springframework.beans.NotWritablePropertyException
另一种可能性是定义一个beanBeanA，并引用另一个beanBeanB，而BeanA中没有相应的setter方法：
@Component
public class BeanA {
private IBeanB dependency;
...
}
@Component
public class BeanB implements IBeanB { ... }
这是SpringXML配置：
<bean id="beanA" class="cn.tuyucheng.taketoday.web.BeanA">
<property name="beanB" ref="beanB" />
</bean>
同样，这只会发生在XML配置中，因为在使用Java@Configuration时，编译器将无法重现此问题。
当然，为了解决这个问题，我们需要为IBeanB添加setter：
@Component
public class BeanA {
private IBeanB dependency;
public void setDependency(final IBeanB dependency) {
this.dependency = dependency;
}
}
6. 原因：org.springframework.beans.factory.CannotLoadBeanClassException
Spring无法加载定义的bean的类时抛出此异常。如果SpringXML配置包含一个根本没有对应类的bean，则可能会发生这种情况。例如，如果类BeanZ不存在，则以下定义将导致异常：
<bean id="beanZ" class="cn.tuyucheng.taketoday.web.BeanZ" />
ClassNotFoundException的根本原因和本例中的完整异常是：
nested exception is org.springframework.beans.factory.BeanCreationException:
...
nested exception is org.springframework.beans.factory.CannotLoadBeanClassException:
Cannot find class [cn.tuyucheng.taketoday.web.BeanZ] for bean with name 'beanZ'
defined in class path resource [beansInXml.xml];
nested exception is java.lang.ClassNotFoundException: cn.tuyucheng.taketoday.web.BeanZ
7. BeanCreationException的孩子
7.1 org.springframework.beans.factory.BeanCurrentlyInCreationException_
BeanCreationException的子类之一是BeanCurrentlyInCreationException。这通常发生在使用构造函数注入时，例如，在循环依赖的情况下：
@Component
public class BeanA implements IBeanA {
private IBeanB beanB;
@Autowired
public BeanA(final IBeanB beanB) {
super();
this.beanB = beanB;
}
}
@Component
public class BeanB implements IBeanB {
final IBeanA beanA;
@Autowired
public BeanB(final IBeanA beanA) {
super();
this.beanA = beanA;
}
}
Spring无法解决这种布线场景，最终结果将是：
org.springframework.beans.factory.BeanCurrentlyInCreationException:
Error creating bean with name 'beanA':
Requested bean is currently in creation: Is there an unresolvable circular reference?
完整的异常非常冗长：
org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'beanA' defined in file [...BeanA.class]:
Unsatisfied dependency expressed through constructor argument with index 0
of type [cn.tuyucheng.taketoday.web.IBeanB]: :
Error creating bean with name 'beanB' defined in file [...BeanB.class]:
Unsatisfied dependency expressed through constructor argument with index 0
of type [cn.tuyucheng.taketoday.web.IBeanA]: :
Error creating bean with name 'beanA': Requested bean is currently in creation:
Is there an unresolvable circular reference?;
nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException:
Error creating bean with name 'beanA':
Requested bean is currently in creation:
Is there an unresolvable circular reference?;
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException:
Error creating bean with name 'beanB' defined in file [...BeanB.class]:
Unsatisfied dependency expressed through constructor argument with index 0
of type [cn.tuyucheng.taketoday.web.IBeanA]: :
Error creating bean with name 'beanA':
Requested bean is currently in creation:
Is there an unresolvable circular reference?;
nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException:
Error creating bean with name 'beanA':
Requested bean is currently in creation: Is there an unresolvable circular reference?
7.2 org.springframework.beans.factory.BeanIsAbstractException
当BeanFactory试图检索和实例化一个声明为抽象的bean时，可能会发生此实例化异常：
public abstract class BeanA implements IBeanA {
// ...
}
我们在XML配置中将其声明为：
<bean id="beanA" abstract="true" class="cn.tuyucheng.taketoday.web.BeanA" />
如果我们尝试通过名称从Spring上下文中检索BeanA，就像在实例化另一个bean时：
@Configuration
public class Config {
@Autowired
BeanFactory beanFactory;
@Bean
public BeanB beanB() {
beanFactory.getBean("beanA");
return new BeanB();
}
}
这将导致以下异常：
org.springframework.beans.factory.BeanIsAbstractException:
Error creating bean with name 'beanA': Bean definition is abstract
以及完整的异常堆栈跟踪：
org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'beanB' defined in class path resource
[org/baeldung/spring/config/WebConfig.class]: Instantiation of bean failed;
nested exception is org.springframework.beans.factory.BeanDefinitionStoreException:
Factory method
[public cn.tuyucheng.taketoday.web.BeanB cn.tuyucheng.taketoday.spring.config.WebConfig.beanB()] threw exception;
nested exception is org.springframework.beans.factory.BeanIsAbstractException:
Error creating bean with name 'beanA': Bean definition is abstract
8. 总结
在本文中，我们了解了如何解决可能导致Spring中的BeanCreationException的各种原因和问题，并很好地掌握了如何解决所有这些问题。
与往常一样，本教程的完整源代码可在GitHub上获得。
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