Springboot中@Import的使用原理
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??org.springframework.boot
??spring-boot-starter-parent
??1.5.6.RELEASE
?
?
??
???org.springframework.boot
???spring-boot-starter-web
??
?
?
??
???
????org.springframework.boot
????spring-boot-maven-plugin
???
??
?
package?com.entity;
?
public?class?User?implements?Serializable{
?
?private?String?name;
?private?String?age;
?
?public?User()?{
??this.name?=?"xiaochen";
??this.age?=?"6";
?}
}
package?com.demo;
?
public?class?ImportUser?implements?ImportSelector?{
?@Override
?public?String[]?selectImports(AnnotationMetadata?importingClassMetadata)?{
??return?new?String[]?{"com.entity.User"};
?}
}
package?com.demo;
?
@Import(ImportUser.class)
@Configuration
public?class?ImportConfiguration?{}
package?com.demo;
public?class?ImportDemo?{
?public?static?void?main(String[]?args)?{
??AnnotationConfigApplicationContext?applicationContext?=?new?AnnotationConfigApplicationContext();
//這里使用register()和scan()方法都可,用scan()方法就不用在配置類中使用@Configuration注解了。
//??applicationContext.register(ImportConfiguration.class);
??applicationContext.scan("com.demo");
??applicationContext.refresh();
??User?user?=?applicationContext.getBean(User.class);
?????System.out.println(user);
?}
}
@Import(EnableAutoConfigurationImportSelector.class)
public?@interface?EnableAutoConfiguration?{}
@SpringBootApplication
public?class?ApplicationStart?{
?public?static?void?main(String[]?args)?{
??SpringApplication.run(ApplicationStart.class,?args);
?}
}
public?ConfigurableApplicationContext?run(String...?args)?{
???refreshContext(context);
}
private?void?refreshContext(ConfigurableApplicationContext?context)?{
??refresh(context);
}
protected?void?refresh(ApplicationContext?applicationContext)?{
??((AbstractApplicationContext)?applicationContext).refresh();
}
?
@Override
public?void?refresh()?throws?BeansException,?IllegalStateException?{
??invokeBeanFactoryPostProcessors(beanFactory);
}
?
protected?void?invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory?beanFactory)?{
?????PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory,?getBeanFactoryPostProcessors());
}?
public?static?void?invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory?beanFactory,?List?beanFactoryPostProcessors)?{
?????invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors,?registry);
}
?
private?static?void?invokeBeanDefinitionRegistryPostProcessors(
???Collection?postProcessors,?BeanDefinitionRegistry?registry)?{
?for?(BeanDefinitionRegistryPostProcessor?postProcessor?:?postProcessors)?{
???postProcessor.postProcessBeanDefinitionRegistry(registry);
?}
}
public?void?postProcessBeanDefinitionRegistry(BeanDefinitionRegistry?registry)?{
??processConfigBeanDefinitions(registry);
}
?
public?void?processConfigBeanDefinitions(BeanDefinitionRegistry?registry)?{
//?Parse?each?@Configuration?class
?ConfigurationClassParser?parser?=?new?ConfigurationClassParser(
????this.metadataReaderFactory,?this.problemReporter,?this.environment,
????this.resourceLoader,?this.componentScanBeanNameGenerator,?registry);
?????parser.parse(candidates);
}
public?void?parse(Set?configCandidates)?{
??processDeferredImportSelectors();
}
private?void?processDeferredImportSelectors()?{
????????String[]?imports?=?deferredImport.getImportSelector().selectImports(configClass.getMetadata());
????????processImports(configClass,?asSourceClass(configClass),?asSourceClasses(imports),?false);
}
private?void?processDeferredImportSelectors()?{
List?deferredImports?=?this.deferredImportSelectors;
this.deferredImportSelectors?=?null;
Collections.sort(deferredImports,?DEFERRED_IMPORT_COMPARATOR);
for?(DeferredImportSelectorHolder?deferredImport?:?deferredImports)?{
?ConfigurationClass?configClass?=?deferredImport.getConfigurationClass();
}
}
private?void?processImports(ConfigurationClass?configClass,?SourceClass?currentSourceClass,Collection?importCandidates,
???????boolean?checkForCircularImports)?throws?IOException?{
????for?(SourceClass?candidate?:?importCandidates)?{
??if?(candidate.isAssignable(ImportSelector.class))?{
//?Candidate?class?is?an?ImportSelector?->?delegate?to?it?to?determine?imports
?????Class?candidateClass?=?candidate.loadClass();
????????????//這里用于實例化ImportSelector的實現(xiàn)類
?????ImportSelector?selector?=?BeanUtils.instantiateClass(candidateClass,ImportSelector.class);
?????ParserStrategyUtils.invokeAwareMethods(selector,?this.environment,this.resourceLoader,?this.registry);
?????if?(this.deferredImportSelectors?!=?null?&&?selector?instanceof?DeferredImportSelector)?{
????this.deferredImportSelectors.add(new?DeferredImportSelectorHolder(configClass,?(DeferredImportSelector)?selector));
???}??
?????}
????}
}
protected?final?SourceClass?doProcessConfigurationClass(ConfigurationClass?configClass,?SourceClass?sourceClass)?throws?IOException?{
//?Process?any?@Import?annotations
?processImports(configClass,?sourceClass,?getImports(sourceClass),?true);
}
private?Set?getImports(SourceClass?sourceClass)?throws?IOException?{
??Set?imports?=?new?LinkedHashSet ();
??Set?visited?=?new?LinkedHashSet ();
??collectImports(sourceClass,?imports,?visited);
??return?imports;
}
private?void?collectImports(SourceClass?sourceClass,?Set?imports,Set ?visited)?throws?IOException?{
?if?(visited.add(sourceClass))?{
??for?(SourceClass?annotation?:?sourceClass.getAnnotations())?{
???String?annName?=?annotation.getMetadata().getClassName();
???if?(!annName.startsWith("java")?&&?!annName.equals(Import.class.getName()))?{
????collectImports(annotation,?imports,?visited);
???}
??}
????????imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(),?"value"));
?}
}
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本文鏈接：
https://blog.csdn.net/qq_21299835/article/details/109695279
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