文章目录

组件添加
- @SpringBootApplication
- @Configuration
- @Bean
- @Condition
- @Improt
- - ImportSelector
  - ImportBeanDefinitionRegistrar
原生配置文件引入
- @ImportResource
配置绑定
- @Component + @ConfigurationProperties
- @ConfigurationProperties + @EnableConfigurationProperties
自动配置原理入门
- 引导加载自动配置类
- - @SpringBootConfiguration
  - @ComponentScan
  - @EnableAutoConfiguration
  - - @AutoConfigurationPackage
    - @Import(AutoConfigurationImportSelector.class)
- 修改默认配置
- 最佳实践

组件添加

@SpringBootApplication

标注这是一个SpringBoot应用

//指定扫描的根目录，如果不标明则默认扫描启动类的下一层所有目录，其中包括所有子目录
@SpringBootApplication(scanBasePackages = "com.atguigu")

@Configuration

告诉springboot这是一个配置类，等于配置文件。

package com.atguigu.boot.config;

import com.atguigu.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）
 *      Lite（proxyBeanMethods = false）
 */
@Configuration(proxyBeanMethods = false)//告诉springboot这是一个配置类==配置文件
public class MyConfig {

    /**
     * 外部无论对配置类中的这个组件注册方法调用多少次获取的都是之前注册容器中的单实例
     * @return
     */
    @Bean("user")
    public User user(){
        User user = new User();
        user.setAge(14);
        user.setName("张三");
        return user;
    }
}

其中proxyBeanMethods = false的作用是如下演示：

package com.atguigu.boot;

import com.atguigu.boot.bean.User;
import com.atguigu.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(scanBasePackages = "com.atguigu")
public class MainApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(MainApplication.class, args);

        //如果@Configuration(proxyBeanMethods=true)代理对象调用方法时springboot总会检查这个组件在容器中是否存在，如果有则直接使用，可以保证组件的单实例
        //如果@Configuration(proxyBeanMethods=false)代理对象调用方法时springboot不会检查这个容器在组件中是否存在，会创建出一个新的对象，容器中不会保存该对象
        MyConfig myConfig = applicationContext.getBean(MyConfig.class);
        User user1 = myConfig.user();
        User user2 = myConfig.user();
        System.out.println(user1 == user2);//false

        
        //默认为单例模式，容器中始终只有一个对象
        User user3 = applicationContext.getBean("user", User.class);
        User user4 = applicationContext.getBean("user", User.class);
        System.out.println(user3 == user4);//true
    }
}

@Bean

用于在配置类中注册bean加入容器中

 @Bean("user")
    public User user(){
        User user = new User();
        user.setAge(14);
        user.setName("张三");
        return user;
    }

@Condition

条件装配：满足Conditional指定的条件，则进行组件注入。

在这里插入图片描述

配置类：

package com.atguigu.boot.config;

import com.atguigu.boot.bean.Pet;
import com.atguigu.boot.bean.User;
import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;


@Configuration(proxyBeanMethods = false)
public class MyConfig {

    @Bean("user")
    public User user(){
        User user = new User();
        user.setAge(14);
        user.setName("张三");
        return user;
    }

    @Bean
    @ConditionalOnMissingBean(User.class)//不存在User这个对象的时候才注册
    public Pet pet(){
        Pet pet = new Pet();
        pet.setKind("猫");
        pet.setName("小白");
        return pet;
    }
}

测试：

package com.atguigu.boot;

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

@SpringBootApplication(scanBasePackages = "com.atguigu")
public class MainApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(MainApplication.class, args);
        
        System.out.println(applicationContext.containsBean("user"));//true 					
        System.out.println(applicationContext.containsBean("pet"));//false
    }
}

@Improt

@Import可以快速给容器中导入一个组件，容器一起动会自动注册这个组件，id默认为全类名。

package com.atguigu.spring_annotation.config;

import com.atguigu.spring_annotation.pojo.Color;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({Color.class})//快速导入组件，id默认为组件全类名，可以写多个
@Configuration
public class MainConfig2 {
  
}

ImportSelector

返回需要导入的组件的全类名数组

package com.atguigu.spring_annotation.config;

import com.atguigu.spring_annotation.condition.MyImportSelector;
import com.atguigu.spring_annotation.pojo.Color;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({Color.class, MyImportSelector.class})//快速导入组件，id默认为组件全类名，可以写多个
@Configuration
public class MainConfig2 {
   
}

package com.atguigu.spring_annotation.condition;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

public class MyImportSelector implements ImportSelector {
    /**
     * 自定义逻辑需要返回的组件
     *
     * @param importingClassMetadata 当前标注@Import注解的类的所有注解信息
     * @return 导入到容器中的组件全类名
     */
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.atguigu.spring_annotation.pojo.Blue", "com.atguigu.spring_annotation.pojo.Yellow"};
    }
}

ImportBeanDefinitionRegistrar

package com.atguigu.spring_annotation.config;

import com.atguigu.spring_annotation.condition.MyImportBeanDefinitionRegistrar;
import com.atguigu.spring_annotation.condition.MyImportSelector;
import com.atguigu.spring_annotation.pojo.Color;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Import({Color.class, MyImportSelector.class, MyImportBeanDefinitionRegistrar.class})//快速导入组件，id默认为组件全类名，可以写多个
@Configuration
public class MainConfig2 {
    
}

package com.atguigu.spring_annotation.condition;

import com.atguigu.spring_annotation.pojo.Red;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

    /**
     * 把所有需要添加到容器中的bean：调用BeanDefinitionRegistry.registerBeanDefinition手动注册
     * @param importingClassMetadata 当前类的注解信息
     * @param registry BeanDefinition注册类
     *
     */
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        boolean containsRed = registry.containsBeanDefinition("red");
        //如果没有red这个组件
        if(!containsRed){
            RootBeanDefinition red = new RootBeanDefinition(Red.class);
            //自定义组件名字
            registry.registerBeanDefinition("red",red);
        }
    }
}

原生配置文件引入

@ImportResource

在任意配置类中使用此注解+路径即可导入xml配置文件，可以用于老项目迁移。

@Configuration(proxyBeanMethods = false)
@ImportResource("classpath:bean.xml")//可以导入spring的xml配置文件
public class MyConfig {
}

配置绑定

@Component + @ConfigurationProperties

application.properties配置文件：

server.port=8181

#封装到JavaBean Car中
mycar.brand=BYD
mycar.price=100000

JavaBean

package com.atguigu.boot.bean;

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

@Data
@Component//只有在容器中的组件才拥有SpringBoot的强大功能
@ConfigurationProperties(prefix = "mycar")//设置前缀为mycar，它将会自动跟字段对应
public class Car {
    private String brand;
    private Integer price;
}

此时容器中就已经有了car对象且将对应的数据注入了。

@ConfigurationProperties + @EnableConfigurationProperties

配置文件与上述一致

JavaBean使用@ConfigurationProperties注解：

package com.atguigu.boot.bean;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;

@Data
@ConfigurationProperties(prefix = "mycar")//设置前缀为mycar，它将会自动跟字段对应
public class Car {
    private String brand;
    private Integer price;
}

配置类使用 @EnableConfigurationProperties注解：

package com.atguigu.boot.config;

import com.atguigu.boot.bean.Car;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(Car.class)
public class MyConfig {

}

此时car也会注入到IOC中

自动配置原理入门

引导加载自动配置类

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {}

@SpringBootConfiguration

代表当前是一个配置类

@ComponentScan

指定扫描哪些Spring注解

@EnableAutoConfiguration

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {}

@AutoConfigurationPackage

自动配置包，指定了默认的包规则

@Import(AutoConfigurationPackages.Registrar.class)  //给容器中导入一个组件
public @interface AutoConfigurationPackage {}

//利用Registrar给容器中导入一系列组件
//将指定的一个包下的所有组件导入进来？MainApplication 所在包下。

@Import(AutoConfigurationImportSelector.class)

1、利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
2、调用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes)获取到所有需要导入到容器中的配置类
3、利用工厂加载 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader)；得到所有的组件
4、从META-INF/spring.factories位置来加载一个文件。
	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-2.3.4.RELEASE.jar包里面也有META-INF/spring.factories

文件里面写死了spring-boot一启动就要给容器中加载的所有配置类
spring-boot-autoconfigure-2.3.4.RELEASE.jar/META-INF/spring.factories
# 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.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.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
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.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
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

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。

修改默认配置

        @Bean
		@ConditionalOnBean(MultipartResolver.class)  //容器中有这个类型组件
		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) //容器中没有这个名字 multipartResolver 的组件
		public MultipartResolver multipartResolver(MultipartResolver resolver) {
            //给@Bean标注的方法传入了对象参数，这个参数的值就会从容器中找。
            //SpringMVC multipartResolver。防止有些用户配置的文件上传解析器不符合规范
			// Detect if the user has created a MultipartResolver but named it incorrectly
			return resolver;
		}
给容器中加入了文件上传解析器；

SpringBoot默认会在底层配好所有的组件。但是如果用户自己配置了以用户的优先

@Bean
	@ConditionalOnMissingBean
	public CharacterEncodingFilter characterEncodingFilter() {
    }

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 —> 组件 —> xxxxProperties里面拿值 ----> application.properties

最佳实践

引入场景依赖
- https://docs.spring.io/spring-boot/docs/current/reference/html/using-spring-boot.html#using-boot-starter
查看自动配置了哪些（选做）
- 自己分析，引入场景对应的自动配置一般都生效了
- 配置文件中debug=true开启自动配置报告。Negative（不生效）\Positive（生效）
是否需要修改
- 参照文档修改配置项
- - https://docs.spring.io/spring-boot/docs/current/reference/html/appendix-application-properties.html#common-application-properties
  - 自己分析。xxxxProperties绑定了配置文件的哪些。
- 自定义加入或者替换组件
- - @Bean、@Component。。。
- 自定义器 XXXXXCustomizer；
- …