4.2 自动配置原理 - SpringBoot自动配置原理 - 《Java企业级框架》

一、SpringBoot特点
- 依赖管理
- 自动配置
二、容器功能
三、自动配置原理
- @SpringBootApplication
- 按需开启自动配置项

一、SpringBoot特点

依赖管理

父项目实现依赖管理

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.4.2</version>
</parent>
<!--spring-boot-starter-parent的父项目-->
<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-dependencies</artifactId>
  <version>2.4.2</version>
</parent>

spring-boot-dependencies中，声明了各个常用依赖包及其版本号

开发导入starter场景启动器

具体的可以查看官方文档

例如：

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

无需关注版本号，自动版本仲裁

引入依赖默认不需要版本号

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
</dependency>

引入非版本仲裁的jar包，需要版本号

可以修改默认版本号

方式一

<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.11</version>
</dependency>

方式二

<properties>
<mysql.version>8.0.11</mysql.version>
</properties>

自动配置

自动配置Tomcat
自动配置SpringMVC

自动配置Web常用功能

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependencies>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter</artifactId>
  <version>2.4.2</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-json</artifactId>
  <version>2.4.2</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-tomcat</artifactId>
  <version>2.4.2</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-web</artifactId>
  <version>5.3.3</version>
  <scope>compile</scope>
</dependency>
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-webmvc</artifactId>
  <version>5.3.3</version>
  <scope>compile</scope>
</dependency>
</dependencies>

默认的包结构

具体的可以查看官方文档

主程序所在包及其下面的所有子包里面的组件都会被默认扫描进来
无需以前的包扫描配置
想要改变扫描路径 @SpringBootApplication(scanBasePackages="com.comprehensive")
- 各种配置都有默认值

按需加载所有自动配置项
- 非常多的starter
- 引入了哪些场景这个场景的自动配置才会开启
- SpringBoot所有的自动配置功能都在 spring-boot-autoconfigure 包里面

二、容器功能

组件添加

@Configuration

配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
配置类本身也是组件
proxyBeanMethods：代理bean的方法
- Full(proxyBeanMethods = true)、【保证每个@Bean方法被调用多少次返回的组件都是单实例的】
- Lite(proxyBeanMethods = false)【每个@Bean方法被调用多少次返回的组件都是新创建的】
- 组件依赖必须使用Full模式默认。其他默认是否Lite模式 ```java package com.comprehensive.boot.bean;

public class User { private String name; private int age; private Pet pet;

public User() {
}

public User(String name, int age) {
    this.name = name;
    this.age = age;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public Pet getPet() {
    return pet;
}

public void setPet(Pet pet) {
    this.pet = pet;
}

@Override
public String toString() {
    return "User{" +
            "name='" + name + '\'' +
            ", age=" + age +
            ", pet=" + pet +
            '}';
}

}

```java
package com.comprehensive.boot.bean;

public class Pet {
    private String name;

    public Pet() {
    }

    public Pet(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Pet{" +
                "name='" + name + '\'' +
                '}';
    }
}

package com.comprehensive.boot.config;

import com.comprehensive.boot.bean.Pet;
import com.comprehensive.boot.bean.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * 1、配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
 * 2、配置类本身也是组件
 * 3、proxyBeanMethods：代理bean的方法
 *      Full(proxyBeanMethods = true)、【保证每个@Bean方法被调用多少次返回的组件都是单实例的】
 *      Lite(proxyBeanMethods = false)【每个@Bean方法被调用多少次返回的组件都是新创建的】
 *      组件依赖必须使用Full模式默认。其他默认是Lite模式
 */
@Configuration(proxyBeanMethods = true) //告诉SpringBoot这是一个配置类 == 配置文件
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

package com.comprehensive.boot;

import com.comprehensive.boot.bean.Pet;
import com.comprehensive.boot.bean.User;
import com.comprehensive.boot.config.MyConfig;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

/**
 * 主程序类
 * @SpringBootApplication:这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        System.out.println(context.getBean(MyConfig.class).getClass()); //class com.comprehensive.boot.config.MyConfig

        //如果@Configuration(proxyBeanMethods = true)代理对象调用方法。SpringBoot总会检查这个组件是否在容器中有
        MyConfig myConfig = context.getBean(MyConfig.class);
        Pet pet1 = myConfig.getPet1();
        Pet pet2 = myConfig.getPet1();
        System.out.println(pet1 == pet2); //true
    }
}

@Import

给容器中自动创建组件、默认组件的名字就是全类名

@Import({User.class, Pet.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

/**
 * 主程序类
 * @SpringBootApplication:这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        String[] beans_user = context.getBeanNamesForType(User.class);
        String[] beans_pet = context.getBeanNamesForType(Pet.class);
        for(String bean_user : beans_user) System.out.println(bean_user);
        for(String bean_pet : beans_pet) System.out.println(bean_pet);
    }
}

@Conditional

条件装配：满足Conditional指定的条件，则进行组件注入

SpringBoot自动配置原理 - 图15

package com.comprehensive.boot.config;

import com.comprehensive.boot.bean.Pet;
import com.comprehensive.boot.bean.User;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

/**
 * 1、配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
 * 2、配置类本身也是组件
 * 3、proxyBeanMethods：代理bean的方法
 *      Full(proxyBeanMethods = true)、【保证每个@Bean方法被调用多少次返回的组件都是单实例的】
 *      Lite(proxyBeanMethods = false)【每个@Bean方法被调用多少次返回的组件都是新创建的】
 *      组件依赖必须使用Full模式默认。其他默认是否Lite模式
 */
@Import({User.class, Pet.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
@ConditionalOnBean(name = "tomcat")
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

/**
 * 主程序类
 * @SpringBootApplication:这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        System.out.println(context.containsBean("user1"));
        System.out.println(context.containsBean("pet1"));
    }
}

package com.comprehensive.boot.config;

import com.comprehensive.boot.bean.Pet;
import com.comprehensive.boot.bean.User;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

/**
 * 1、配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
 * 2、配置类本身也是组件
 * 3、proxyBeanMethods：代理bean的方法
 *      Full(proxyBeanMethods = true)、【保证每个@Bean方法被调用多少次返回的组件都是单实例的】
 *      Lite(proxyBeanMethods = false)【每个@Bean方法被调用多少次返回的组件都是新创建的】
 *      组件依赖必须使用Full模式默认。其他默认是否Lite模式
 */
@Import({User.class, Pet.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
@ConditionalOnBean(name = {"user1", "pet1", "tomcat"})
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

/**
 * 主程序类
 * @SpringBootApplication:这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        System.out.println(context.containsBean("user1"));
        System.out.println(context.containsBean("pet1"));
    }
}

原生配置文件导入

@ImportResource

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="user_forImportResource" class="com.comprehensive.boot.bean.User"/>
    <bean id="pet_forImportResource" class="com.comprehensive.boot.bean.Pet"/>

</beans>

package com.comprehensive.boot.config;

import com.comprehensive.boot.bean.Pet;
import com.comprehensive.boot.bean.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.ImportResource;

/**
 * 1、配置类里面使用@Bean标注在方法上给容器注册组件，默认也是单实例的
 * 2、配置类本身也是组件
 * 3、proxyBeanMethods：代理bean的方法
 *      Full(proxyBeanMethods = true)、【保证每个@Bean方法被调用多少次返回的组件都是单实例的】
 *      Lite(proxyBeanMethods = false)【每个@Bean方法被调用多少次返回的组件都是新创建的】
 *      组件依赖必须使用Full模式默认。其他默认是否Lite模式
 */
@Import({User.class, Pet.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
@ImportResource("beans.xml")
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

/**
 * 主程序类
 * @SpringBootApplication:这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        System.out.println(context.containsBean("user_forImportResource"));
        System.out.println(context.containsBean("pet_forImportResource"));
    }
}

配置绑定

@ConfigurationProperties

方式一：@Component + @ConfigurationProperties

package com.comprehensive.boot.bean;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

/**
 * 只有在容器中的组件，才会拥有SpringBoot提供的强大功能
 */
@Component
@ConfigurationProperties(prefix = "mycar")
public class Car {
    private String brand;
    private Integer price;

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public Integer getPrice() {
        return price;
    }

    public void setPrice(Integer price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", price=" + price +
                '}';
    }
}

@RestController
public class HelloController {
    @Autowired
    private Car car;
    @RequestMapping("/test_ConfigurationProperties")
    public Car car() {
        return car;
    }
}

方式二：@EnableConfigurationProperties + @ConfigurationProperties

@Component注解注释后，会发现如下报错。原因是未在容器中注册car这个JavaBean

—在配置类中加@EnableConfigurationProperties

@Import({User.class, Pet.class})
@Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
@ImportResource("beans.xml")
@EnableConfigurationProperties(Car.class)
public class MyConfig {
    @Bean //给容器中添加组件，以方法名作为组件id，返回类型就是组件类型，返回的值就是组件在容器中的实例
    public User user1() {
        User user1 = new User("comprehensive", 22);
        user1.setPet(getPet1());
        return user1;
    }
    @Bean(name = "pet1")
    public Pet getPet1() {
        return new Pet("tomcat");
    }
}

三、自动配置原理

@SpringBootApplication

组合注解，由下列注解合并实现

@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 {}

@SpringBootConfiguration

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration //@Configuration: 代表当前是一个配置类
public @interface SpringBootConfiguration {
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

@ComponentScan

指定扫描哪些，Spring注解

@EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage //自动配置包,指定了默认的包规则
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {}

@AutoConfigurationPackage

我们点开@AutoConfigurationPackage继续往深层探索

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class) //给容器中导入一个组件
public @interface AutoConfigurationPackage {}

不难发现，这里有一个@import注解，
导入了AutoConfigurationPackages.Registrar这个类，继续往深层探究，看看这个类有什么作用

@Import(AutoConfigurationImportSelector.class)

我们点开AutoConfigurationImportSelector这个类继续往深层探索，发现有这么一个方法

@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
    if (!isEnabled(annotationMetadata)) {
        return NO_IMPORTS;
    }
    AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata);
    return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
}

原来，SpringBoot是利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
继续往深层次探索，看看这个方法具体是怎么实现的

不难发现，getCandidateConfigurations(annotationMetadata, attributes);这个方法可以获取到所有需要导入到容器中的配置类(候选)

继续Debug，选中getCandidateConfigurations(annotationMetadata, attributes);这个方法，点击步入

继续深入探索，点击loadFactoryNames(getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());这个方法，发现：利用工厂加载Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader);得到所有的组件

继续深入探索，在Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader);这个方法上打一个断点，进行调试。发现：从META-INF/spring.factories位置来加载一个文件，也就是默认扫描我们当前系统里面所有META-INF/spring.factories位置的文件

spring-boot-autoconfigure-2.4.2.jar包里面也有META-INF/spring.factories，点开看看，发现AutoConfigure这一类别，总共有130个配置类。回想下之前的getCandidateConfigurations(annotationMetadata, attributes);方法，导入到容器中的配置类刚好是130个。

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.neo4j.Neo4jAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

按需开启自动配置项

虽然我们127个场景的所有自动配置启动的时候默认全部加载。xxxxAutoConfiguration
按照条件装配规则（@Conditional），最终会按需配置。

总结：
• SpringBoot先加载所有的自动配置类 xxxxxAutoConfiguration
• 每个自动配置类按照条件进行生效，默认都会绑定配置文件指定的值。xxxxProperties里面拿。xxxProperties和配置文件进行了绑定
• 生效的配置类就会给容器中装配很多组件
• 只要容器中有这些组件，相当于这些功能就有了
• 定制化配置
• 用户直接自己@Bean替换底层的组件
• 用户去看这个组件是获取的配置文件什么值就去修改。
xxxxxAutoConfiguration —-> 导入组件 —-> 从xxxxProperties里面拿值 ——> 从application.properties里面拿值

SpringBoot自动配置原理