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This article will explain in detail how to understand the difference between BeanFactory and FactoryBean in Spring. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have some understanding of the relevant knowledge after reading this article.

There are two interfaces, BeanFactory and FactoryBean, in Spring, which are similar in name and easy to get confused.

1. BeanFactory

BeanFactory is an interface, which is the top-level specification of the factory in Spring and the core interface of SpringIoc containers. It defines general methods for managing Bean, such as getBean (), containsBean (), and so on. The containers of Spring are its specific implementations, such as:

DefaultListableBeanFactory XmlBeanFactory ApplicationContext

These implementation classes have different extensions from different dimensions.

1.1 BenaFactory source code

Public interface BeanFactory {/ * is used to obtain references to instances and to distinguish between FactoryBean. * if you use the name myJndiObject of bean to obtain FactoryBean, you will return a factory instead of a factory instance. If you need to get a factory instance, you need to escape. * / String FACTORY_BEAN_PREFIX = "&"; / * get the specified bean instance according to the name of bean, which can be shared or independent. * / Object getBean (String name) throws BeansException; / * get the specified bean instance according to the name of bean. The instance can be shared or independent. And a type of test is added. * / T getBean (String name, Class requiredType) throws BeansException; Object getBean (String name, Object...) Args) throws BeansException; / * returns a matching bean instance based on the given type. * / T getBean (Class requiredType) throws BeansException; T getBean (Class requiredType, Object...) Args) throws BeansException; / * check whether the bean * / boolean containsBean (String name) is included in the bean container of spring; / * determine whether the scope of bean is singleton * / boolean isSingleton (String name) throws NoSuchBeanDefinitionException; / * determine whether the scope of bena is prototype * / boolean isPrototype (String name) throws NoSuchBeanDefinitionException; / * check whether the bean of the given name matches the specified type. More specifically, by checking the given bean, return the target object of the specified type * / boolean isTypeMatch (String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException; boolean isTypeMatch (String name, Class typeToMatch) throws NoSuchBeanDefinitionException; / * * get the class type of bean with the given name * / Class getType (String name) throws NoSuchBeanDefinitionException; / * get the alias of the given bean name. If you retrieve it according to the alias, you will get the original bean name. * String [] getAliases (String name);}

1.2 usage scenarios

Get Bean (byName or byType) from the Ioc container: context.getBean ("father", Father.class), context.getBean ("father") to retrieve whether the Ioc container contains the specified Bean: context.containsBean ("father") to determine whether the Bean is a singleton: context.isSingleton ("father")

II. FactoryBean

First of all, it's a Bean, but it's not just a Bean. It is a factory Bean that can produce or modify the generation of objects, similar to factory patterns and decorator patterns in design patterns. It can produce an object when needed, and is not limited to itself, it can return any instance of Bean.

2.1 FactoryBean source code

Public interface FactoryBean {/ * get bean instance from factory * / T getObject () throws Exception; / * get the type of bean instance object from factory * / Class getObjectType (); / * whether the object created by the factory is singleton * / boolean isSingleton ();}

As can be seen from the interfaces it defines, FactoryBean represents the responsibility of a factory. That is, if a Bean An implements the FactoryBean interface, then A becomes a factory. According to A's name, what is actually obtained is the object returned by the factory calling getObject (), not An itself. If you want to get an instance of factory An itself, you need to precede the name with a'& 'symbol.

GetObject ('name') returns the instance in the factory getObject (' & name') returns the instance of the factory itself

In general, bean does not have to implement the factory pattern on its own, and the Spring container acts as a factory; but in a few cases, the bean in the container is itself a factory to generate other bean instances. Other bean instances generated by the factory bean are no longer generated by the Spring container, so unlike the normal bean configuration, the class element is no longer required.

2.2 exampl

First define a Bean implementation FactoryBean interface:

@ Componentpublic class MyBean implements FactoryBean {private String message; public MyBean () {this.message = "initialize the instance by construction method";} public MyBean (String message) {this.message = message;} @ Override public Object getObject () throws Exception {/ / it is not necessary to return an instance of MyBean itself, but can be an instance of any other object return new MyBean ("create an instance through FactoryBean.getObject ()");} @ Override public Class getObjectType () {return MyBean.class } public String getMessage () {return message;} @ Override public boolean isSingleton () {return false;}}

MyBean implements three methods of the FactoryBean interface. GetObject () can return an instance of any object. Here, the test returns an instance of MyBean itself, and assigns a value to the message field before returning. Also assign a value to message in the constructor. Then in the test code, first get the Bean instance by name, print the content of message, and then get the instance and print the message content by & + name.

@ RunWith (SpringRunner.class) @ SpringBootTest (classes = HelloApplication.class) public class FactoryBeanTest {@ Autowired private ApplicationContext context; @ Test public void test () {MyBean myBean1 = (MyBean) context.getBean ("myBean"); / / return the instance in the factory and call FactoryBean.getObject () to create the instance System.out.println ("myBean1 =" + myBean1.getMessage (); MyBean myBean2 = (MyBean) context.getBean ("& myBean")) / / return the factory itself and initialize the instance System.out.println ("myBean2 =" + myBean2.getMessage ()); System.out.println ("myBean1.equals (myBean2) =" + myBean1.equals (myBean2));}}

Print the results:

MyBean1 = create the instance through FactoryBean.getObject () myBean2 = initialize the instance by construction method myBean1.equals (myBean2) = false

2.3 usage scenarios

Having said so much, why is there such a thing as FactoryBean? is there any specific function?

One of the most typical applications of FactoryBean in Spring is to create proxy objects for AOP.

We know that AOP is actually a proxy object created by Spring at run time, that is, it is created at run time rather than defined in the first place, which is in line with the factory method pattern. More vividly, the AOP proxy object creates a proxy object at run time through the reflection mechanism of Java, and weaves the corresponding method into the target method of the proxy object according to the business requirements. This object is called ProxyFactoryBean in Spring.

Therefore, FactoryBean provides a more flexible way for us to instantiate Bean, and we can create more complex Bean instances through FactoryBean.

III. Differences

Both of them are factories, but FactoryBean is essentially a Bean and is also managed by BeanFactory. BeanFactory is the top-level interface of the Spring container, and FactoryBean is more similar to a user-defined factory interface.

On how to understand the difference between BeanFactory and FactoryBean in Spring is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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