Talk to the @SpringBootApplication annotations for Springboot startup

By Spring

A few days ago we learned how to create a springboot project. Today we talk about how it runs and why we don’t need to write heavy configuration

@SpringBootApplication

First, let’s take a look at this annotation. It is used to mark in the main program, indicating that it is a springboot project

@Target({ElementType.TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @SpringBootConfiguration

 @EnableAutoConfiguration

 @ComponentScan(

 excludeFilters = {

 @Filter(type = FilterType.CUSTOM,classes = {TypeExcludeFilter.class}),

 @Filter( type = FilterType.CUSTOM,classes = {AutoConfigurationExcludeFilter.class})

}

)

 public @interface SpringBootApplication {
}< /pre>

After clicking into the @SpringBootApplication annotation, we will focus on the last three annotations

< span>@ComponentScan (Package Scan)

  • component is a component, scan is a scan, so the meaning of this annotation is to scan the component,

  • componentScan is to scan all the packages under the marked class The components that need to be injected, inject them, here he is reflected in @SpringBootApplication, so this annotation will automatically inject all the components in the package where the main program is located

  • In the ssm project, we needed to configure our package scanning

    < /li> 
 
package="com.xxx">

< h5 class="md-end-block md-he ading">@EnableAutoConfiguration (enable auto-assembly) 

@Target({ElementType. TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @AutoConfigurationPackage

 @Import({AutoConfigurationImportSelector.class})

 public @interface EnableAutoConfiguration {

 String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

?

 Class[] exclude() default {};

?

 String[] excludeName() default {};

 }

Here we focus on two annotations

1. @AutoConfigurationPackage

 
 @Target({ElementType.TYPE} )

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @Import({Registrar.class})

 public @interface AutoConfigurationPackage {

 }

In this comment, Mainly to get the components under the package where our annotations are located to register

 
 static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

 Registrar() {

}

?

 //metadata is the meta information where our annotations are located

 public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {

 //Look here for all the components under the package where we annotate Sign up

 AutoConfigurationPackages.register(registry, (new AutoConfigurationPackages.PackageImport(metadata)).getPackageName( ));

}

?

 public Set determineImports(AnnotationMetadata metadata) {

 return Collections.singleton(new AutoConfigurationPackages.PackageImport(metadata));

}

 }





register< /strong>Method: Use AutoConfigurationPackages to register the components under the package


 




 private  static final String BEAN = AutoConfigurationPackages.class.getName();

?

 public static void register(BeanDefinitionRegistry registry, String... packageNames) {

 //First determine whether the entire BEAN is registered

 if (registry.containsBeanDefinition(BEAN)) {

 //Get bean definition

 BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);

 //Get constructor parameter values ​​through bean

 ConstructorArgumentValues ​​constructorArguments = beanDefinition.getConstructorArgumentValues();

 //Add parameter values,

 constructorArguments.addIndexedArgumentValue(0, addBasePackages(constructorArguments, packageNames));

} else {

 //Create a new bean definition

 GenericBeanDefinition beanDefinition = new GenericBeanDefinition();

 //Set the type of bean to AutoConfigurationPackages type

 beanDefinition.setBeanClass(AutoConfigurationPackages.BasePackages.class);

 beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, packageNames);

 beanDefinition.setRole(2);

 //Registration of beans

 registry.registerBeanDefinition(BEAN, beanDefinition);

}

 }






二、@Import( {AutoConfigurationImportSelector.class})


Assemble our automatic configuration import selector


We click into this class, below there is a method getAutoConfigurationEntry to get the entrance of automatic assembly,


 




protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) {

 if (!this.isEnabled(annotationMetadata)) {

 return EMPTY_ENTRY;

} else {

 AnnotationAttributes attributes = this.getAttributes(annotationMetadata);

 List configurations = this.getCandidateConfigurations(annotationMetadata, attributes) ;

 configurations = this.removeDuplicates(configurations);

 Set exclusions = this.getExclusions(annotationMetadata, attributes) ;

 this.checkExcludedClasses(configurations, exclusions);

 configurations.removeAll(exclusions);

 configurations = this.filter(configurations, autoConfigurationMetadata);

 this.fireAutoConfigurationImportEvents(configurations, exclusions);

 return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);

}

 }






This method is mainly Get a collection of configurations. Here we click into the getCandidateConfigurations method


 
 
 
protected List getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {

 List configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());

 Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");

 return configurations;

 }






Let’s look at him first Red error message: No automatic configuration class was found in META-INF/spring.factories. According to his error message, we can conclude that he obtained our automatic configuration information from META-INF/spring.factories


< span class="md-line md-end-block">We can also click into this loadFactoryNamesthis method span>




 public  static List loadFactoryNames(Class factoryClass, @Nullable ClassLoader classLoader) {

 String factoryClassName = factoryClass.getName();

 //The following method loadSpringFactories is called

 return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList() );

}

?

 private static Map > loadSpringFactories(@Nullable ClassLoader classLoader) {

 MultiValueMap result = (MultiValueMap)cache.get(classLoader);

 if (result != null) {

 return result;

} else {

 try {

 //According to the class loader to obtain the information in the configuration file< /span>

 Enumeration urls = classLoader != null? classLoader.getResources("META-INF/spring.factories"): ClassLoader.getSystemResources( "META-INF/spring.factories");

 LinkedMultiValueMap result = new LinkedMultiValueMap();

?

 while(urls.hasMoreElements()) {

 URL url = (URL)urls.nextElement();

 UrlResource resource = new UrlResource(url);

 //The configuration information is transformed into properties after many conversions span>

 Properties properties = PropertiesLoaderUtils.loadProperties(resource);

 Iterator var6 = properties.entrySet().iterator();

 //Get all configuration information in a loop

 while(var6.hasNext()) {

 Entry entry = (Entry)var6.next();

 String factoryClassName = ((String)entry.getKey()).trim();

 String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());

 int var10 = var9.length;

?

 for(int var11 = 0; var11 var11) {

 String factoryName = var9[var11];

 result.add(factoryClassName, factoryName.trim());

}

}

}

?

 cache.put(classLoader, result);

 return result;

} catch (IOException var13) {

 throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);

}

}

 }






And this configuration file is in Where?


Find our spring-boot-autoconfigure in the External Libraries of our project Medium


share picture


share pictureThis completes some of our default automatic assembly


@SpringBootConfiguration


This method is relatively simple, indicating that this is a configuration class


 < div class="code"> 


 @Target({ElementType.TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Configuration

 public @interface SpringBootConfiguration {

 }





This is the end of our three comments. If you have any questions, please point out the big guys. Thank you.  span>




Have struggles, have failed, but still get up and continue fighting




 @Target({ElementType.TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @SpringBootConfiguration

 @EnableAutoConfiguration

 @ComponentScan(

 excludeFilters = {

 @Filter(type = FilterType.CUSTOM,classes = {TypeExcludeFilter.class}),

 @Filter( type = FilterType.CUSTOM,classes = {AutoConfigurationExcludeFilter.class})

}

)

 public @interface SpringBootApplication {
}< /pre>
package="com.xxx">




@Target({ElementType.TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @AutoConfigurationPackage

 @Import({AutoConfigurationImportSelector.class})

 public @interface EnableAutoConfiguration {

 String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

?

 Class[] exclude() default {};

?

 String[] excludeName() default {};

 }




 @Target({ElementType.TYPE})

 @Retention(RetentionPolicy.RUNTIME)

 @Documented

 @Inherited

 @Import({Registrar.class})

 public @interface AutoConfigurationPackage {

 }




 static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {

 Registrar() {

}

?

 //metadata is the meta information where our annotations are located

 public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {

 //Look here for all the components under the package where we annotate Sign up

 AutoConfigurationPackages.register(registry, (new AutoConfigurationPackages.PackageImport(metadata)).getPackageName( ));

}

?

 public Set determineImports(AnnotationMetadata metadata) {

 return Collections.singleton(new AutoConfigurationPackages.PackageImport(metadata));

}

 }



 private static final String BEAN = AutoConfigurationPackages.class.getName();

?

 public static void register(BeanDefinitionRegistry registry, String... packageNames) {

 //First determine whether the entire BEAN is registered

 if (registry.containsBeanDefinition(BEAN)) {

 //Get bean definition

 BeanDefinition beanDefinition = registry.getBeanDefinition(BEAN);

 //Get constructor parameter values ​​through bean

 ConstructorArgumentValues ​​constructorArguments = beanDefinition.getConstructorArgumentValues();

 //Add parameter values,

 constructorArguments.addIndexedArgumentValue(0, addBasePackages(constructorArguments, packageNames));

} else {

 //Create a new bean definition

 GenericBeanDefinition beanDefinition = new GenericBeanDefinition();

 //Set the type of bean to AutoConfigurationPackages type

 beanDefinition.setBeanClass(AutoConfigurationPackages.BasePackages.class);

 beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0, packageNames);

 beanDefinition.setRole(2);

 //Registration of beans

 registry.registerBeanDefinition(BEAN, beanDefinition);

}

 }




protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) {

 if (!this.isEnabled(annotationMetadata)) {

 return EMPTY_ENTRY;

} else {

 AnnotationAttributes attributes = this.getAttributes(annotationMetadata);

 List configurations = this.getCandidateConfigurations(annotationMetadata, attributes) ;

 configurations = this.removeDuplicates(configurations);

 Set exclusions = this.getExclusions(annotationMetadata, attributes) ;

 this.checkExcludedClasses(configurations, exclusions);

 configurations.removeAll(exclusions);

 configurations = this.filter(configurations, autoConfigurationMetadata);

 this.fireAutoConfigurationImportEvents(configurations, exclusions);

 return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions);

}

 }




protected List getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {

 List configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());

 Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");

 return configurations;

 }




 public static List loadFactoryNames(Class factoryClass, @Nullable ClassLoader classLoader) {

 String factoryClassName = factoryClass.getName();

 //The following method loadSpringFactories is called

 return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList() );

}

?

 private static Map > loadSpringFactories(@Nullable ClassLoader classLoader) {

 MultiValueMap result = (MultiValueMap)cache.get(classLoader);

 if (result != null) {

 return result;

} else {

 try {

                //根据类加载器去获取配置文件里的信息

                  Enumeration urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");

                  LinkedMultiValueMap result = new LinkedMultiValueMap();

  ?

                  while(urls.hasMoreElements()) {

                      URL url = (URL)urls.nextElement();

                      UrlResource resource = new UrlResource(url);

                    //配置信息经过多次转换最终成为properties形式

                      Properties properties = PropertiesLoaderUtils.loadProperties(resource);

                      Iterator var6 = properties.entrySet().iterator();

                  //循环获取所有的配置信息

                      while(var6.hasNext()) {

                          Entry entry = (Entry)var6.next();

                          String factoryClassName = ((String)entry.getKey()).trim();

                          String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());

                          int var10 = var9.length;

  ?

                          for(int var11 = 0; var11 < var10; ++var11) {

                              String factoryName = var9[var11];

                              result.add(factoryClassName, factoryName.trim());

                          }

                      }

                  }

  ?

                  cache.put(classLoader, result);

                  return result;

              } catch (IOException var13) {

                  throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);

              }

          }

      }




  @Target({ElementType.TYPE})

  @Retention(RetentionPolicy.RUNTIME)

  @Documented

  @Configuration

  public @interface SpringBootConfiguration {

  }






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