源码学习系列之SpringBoot自动配置（篇一）

源码学习系列之SpringBoot自动配置源码学习（篇一）

ok，本博客尝试跟一下Springboot的自动配置源码，做一下笔记记录，自动配置是Springboot的一个很关键的特性，也容易被忽略的属性，因为这个属性被包括在@SpringBootApplication注解里，所以不去跟一下源码都不知道还有这个属性，ps：本博客源码基于SpringBoot1.5.7版本

@SpringBootApplication

ok，跟一下@SpringBootApplication，发现@SpringBootApplication其实是一个复合的注解，由很多注解构成，@EnableAutoConfiguration其实只是其一部分，@EnableAutoConfiguration就是开启自动配置的注解

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.core.annotation.AliasFor;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration 
@EnableAutoConfiguration //自动配置注解
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    ....
    Class[] scanBasePackageClasses() default {};
}

@EnableAutoConfiguration

点进@EnableAutoConfiguration，比较重要的列出来：

• @AutoConfigurationPackage
• @Import({EnableAutoConfigurationImportSelector.class})

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({EnableAutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    Class[] exclude() default {};

    String[] excludeName() default {};
}

@AutoConfigurationPackage

先看@AutoConfigurationPackage源码，这个注解是开启自动配置包的，关注点在@Import({Registrar.class})，核心在Registrar类

备注：@import注解是Spring的底层注解，作用是导入一个组件到容器里

package org.springframework.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.boot.autoconfigure.AutoConfigurationPackages.Registrar;
import org.springframework.context.annotation.Import;

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

Registrar 类是AutoConfigurationPackages类的静态内部类，

 static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
        Registrar() {
        }

        public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
            AutoConfigurationPackages.register(registry, (new AutoConfigurationPackages.PackageImport(metadata)).getPackageName());
        }

        public Set