springboot自动配置原理

启动类

package com.liouwb.springbootdemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author liouwb
 */
@SpringBootApplication
public class SpringbootDemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringbootDemoApplication.class, args);
    }

}

启动类只有@SpringBootApplication注解和一个main方法

• @springBootApplication注解，说明这是一个Spring Boot应用

@SpringBootApplication 注解

• SpringBootApplication注解源码

@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 {

• 从上面注解源码可以看出，@SpringBootApplication是一个复合注解
• @Target @Retention @Documented @Inherited四个是元注解不用考虑
• @SpringBootConfiguration 说明这个一个SpringBoot配置
• @EnableAutoConfiguration 开启自动配置功能

@SpringBootConfiguration注解

• @SpringBootConfiguration 源码

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {

• @Configuration 说明这个一个配置类(对应Spring的xml 配置文件)

@EnableAutoConfiguration注解

• @EnableAutoConfiguration 注解源码

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

• @AutoConfigurationPackage 自动配置包
• @Import Spring底层注解 给容器中导入一个组件

@AutoConfigurationPackage注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {

• • @Import Spring底层注解 给容器中导入一个组件

@Import 注解

• AutoConfigurationImportSelector ：自动配置导入选择器
• AutoConfigurationPackages.Registrar.class: 将主启动类的所在包及包下面所有子包里面的所有组件扫描到Spring容器

AutoConfigurationImportSelector 类

• getCandidateConfigurations() 方法

	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
   	List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
   			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;
   }

• SpringFactoriesLoader类的 loadFactoryNames() 方法

   public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
       String factoryTypeName = factoryType.getName();
       return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
   }

• loadSpringFactories() 方法
  

• spring.factories 文件，自动配置都在springboot-autoconfigure的jar包中
  

• 看下自动配置类的代码
  

• 就是一个平常经常写的java配置类

自动配置原理

1. SpringBoot在启动的会扫描classpath类路径下的META-INF/spring.factories
2. 获取EnableAutoConfiguration指定的值，导入容器，进行自动配置工作