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This article mainly explains "how to define Bean loading order in Spring". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "how to define Bean loading order in Spring".

The order in which Spring containers load bean is uncertain, and the Spring framework does not agree on specific sequential logic specifications. But Spring guarantees that if A depends on B (such as the variable @ Autowired B in beanA), then B will be loaded before A.

Logical judgment

Control the initialization order of AMagi B in the business layer.

The constructor relies on @ Componentpublicclass DemoA {private String name = "demo A"; public DemoA (DemoB demoB) {System.out.println (name);}} @ Componentpublicclass DemoB {private String name = "demoB"; public CDemoB () {System.out.println (name);}} when constructing A, you will first construct B using @ DependsOn.

The @ DependsOn in Spring guarantees that the dependent bean is created by the container before the current bean

The @ DependsOn annotation can be defined on classes and methods, meaning that my component depends on another component, which means that the dependent component will register with the IOC container before that component.

Use annotations on the class: package com.spring.master.spring;import org.springframework.stereotype.Component;/** * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:55 * @ describtion industry is more diligent than playful. * / @ Componentpublic class EventSource {public EventSource () {System.out.println ("event source creation");} package com.spring.master.spring.dependson;import org.springframework.stereotype.Component;/** * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:56 * @ describtion. * / @ Componentpublic class EventListener {public EventListener () {System.out.println ("listener creation");} package com.spring.master.spring.dependson;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Configuration;/** * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:57 * @ describtion. * / @ Configuration@ComponentScan (basePackages = "com.spring.master.spring") public class SpringConfig {} start the service: event source create listener create remarks: Spring default scan package will scan and load files according to the location of the folder. * * Annotation using @ DependsOn: package com.spring.master.spring Import org.springframework.context.annotation.DependsOn;import org.springframework.stereotype.Component;/** * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:55 * @ describtion What you do is done in thought, but it is destroyed by doing as you wish. * / @ Component@DependsOn (value = {"eventListener"}) public class EventSource {public EventSource () {System.out.println ("event source creation");}} start the service: note: package com.spring.master.spring;import org.springframework.context.annotation.DependsOn;import org.springframework.stereotype.Component for listener creation event source creation method / * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:55 * @ describtion What you do is done in thought, but it is destroyed by doing as you wish. * / / @ Component//@DependsOn (value = {"eventListener"}) public class EventSource {public EventSource () {System.out.println ("event source creation");} package com.spring.master.spring.dependson;import org.springframework.stereotype.Component;/** * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:56 * @ describtion. * / / @ Componentpublic class EventListener {public EventListener () {System.out.println ("listener creation");} package com.spring.master.spring.dependson;import com.spring.master.spring.EventSource;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Configuration;import org.springframework.context.annotation.DependsOn / * @ author Huan Lee * @ version 1.0 * @ date 2020-09-22 15:57 * @ describtion What you do is done in thought, but it is destroyed by doing as you wish. * / @ Configuration@ComponentScan (basePackages = "com.spring.master.spring") public class SpringConfig {@ Bean @ DependsOn (value = {"eventListener"}) public EventSource eventSource () {return new EventSource ();} @ Bean public EventListener eventListener () {return new EventListener ();}} start service output: listener creates event source to create BeanFactoryPostProcessor

Before the container loads the bean: BeanFactoryPostProcessor allows us to modify the BeanDefinition in the application context before the container loads any bean

In this case, you can put the initialization logic of An in a BeanFactoryPostProcessor. @ Componentpublic class ABeanFactoryPostProcessor implements BeanFactoryPostProcessor {@ Override public void postProcessBeanFactory (ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {A.initA ();}} puts the initialization logic in A before loading bean, which is suitable for loading the global configuration of the system, but in this way the initialization logic cannot rely on the state of bean. BeanPostProcessor@Componentpublicclass HDemo1 {private String name = "h demo 1"; public HDemo1 () {System.out.println (name);}} @ Componentpublicclass HDemo2 {private String name = "h demo 2"; public HDemo2 () {System.out.println (name);}} @ Componentpublicclass DemoBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter implements BeanFactoryAware {private ConfigurableListableBeanFactory beanFactory @ Override public void setBeanFactory (BeanFactory beanFactory) {if (! (beanFactory instanceof ConfigurableListableBeanFactory)) {thrownew IllegalArgumentException ("AutowiredAnnotationBeanPostProcessor requires a ConfigurableListableBeanFactory:" >

Please focus on postProcessBeforeInstantiation, which is called before a bean is instantiated, which gives us a chance to control the loading order of the bean.

Thank you for reading, these are the contents of "how to define Bean loading order in Spring". After the study of this article, I believe you have a deeper understanding of how to define Bean loading order in Spring, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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