spring boot2学习笔记

一， spring boot2核心技术基础入门

1.spring能做什么

1.1 spring的能力


二 、为什么用SpringBoot

Spring Boot makes it easy to create stand-alone, production-grade Spring based Applications that you can “just run”.

能快速创建出生产级别的Spring应用

2.1、SpringBoot优点

• Create stand-alone Spring applications

• • 创建独立Spring应用

• Embed Tomcat, Jetty or Undertow directly (no need to deploy WAR files)

• • 内嵌web服务器

• Provide opinionated ‘starter’ dependencies to simplify your build configuration

• • 自动starter依赖，简化构建配置

• Automatically configure Spring and 3rd party libraries whenever possible

• • 自动配置Spring以及第三方功能

• Provide production-ready features such as metrics, health checks, and externalized configuration

• • 提供生产级别的监控、健康检查及外部化配置

• Absolutely no code generation and no requirement for XML configuration

• • 无代码生成、无需编写XML

• 三 ， spring boot开发文档

四，spring boot入门

1，hello world

导入依赖

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

 这个依赖导入了开发中大部分的jar包

1.1 编写主程序


@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String handle01(){
        return "hello,Spring boot 2!";
    }
}

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

文件的部署

用spring boot的插件把整个项目打包成jar包

<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


五， 了解自动配置原理

1.0 依赖管理

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.4</version>
    </parent>

他的父项目

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-dependencies</artifactId>
    <version>2.6.4</version>
  </parent>
  

几乎声明了所有开发中常用的依赖版本，和依赖所对应的版本号

如：


因此在prom.xml中导入依赖的时候不需要写对应的的版本号


3. 如何想自行更换版本：如更换mysql驱动

​ 上mvn仓库Maven Repository: Search/Browse/Explore (mvnrepository.com)


​ 在porm。xml中输入

<properties>
            <mysql.version>5.1.43</mysql.version>
    </properties>

依赖树


2.容器功能

2.1 组件添加

1. @Configuration

   基本使用

   #############################Configuration使用示例######################################################
   /**
    * 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
    *
    *
    *
    */
   @Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
   public class MyConfig {
   
       /**
        * Full: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对象
        * @return
        */
       @Bean //给容器中添加组件。以方法名作为组件的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 user01(){
           User zhangsan = new User("zhangsan", 18);
           //user组件依赖了Pet组件
           zhangsan.setPet(tomcatPet());
           return zhangsan;
       }
   
       @Bean("tom")
       public Pet tomcatPet(){
           return new Pet("tomcat");
       }
   }
   
   
   ################################@Configuration测试代码如下########################################
   @SpringBootConfiguration
   @EnableAutoConfiguration
   @ComponentScan("com.atguigu.boot")
   public class MainApplication {
   
       public static void main(String[] args) {
           //1、返回我们IOC容器
           ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);
   
           //2、查看容器里面的组件
           String[] names = run.getBeanDefinitionNames();
           for (String name : names) {
               System.out.println(name);
           }
   
           //3、从容器中获取组件
   
           Pet tom01 = run.getBean("tom", Pet.class);
   
           Pet tom02 = run.getBean("tom", Pet.class);
   
           System.out.println("组件："+(tom01 == tom02));
   
   
           //4、com.atguigu.boot.config.MyConfig$$EnhancerBySpringCGLIB$$51f1e1ca@1654a892
           MyConfig bean = run.getBean(MyConfig.class);
           System.out.println(bean);
   
           //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。
           //保持组件单实例
           User user = bean.user01();
           User user1 = bean.user01();
           System.out.println(user == user1);
   
   
           User user01 = run.getBean("user01", User.class);
           Pet tom = run.getBean("tom", Pet.class);
   
           System.out.println("用户的宠物："+(user01.getPet() == tom));
   
   
   
       }
   }
   

2. @Bean、@Component、@Controller、@Service、@Repository

3. @ComponentScan、@Import

    * 4、@Import({User.class, DBHelper.class})
    *      给容器中自动创建出这两个类型的组件、默认组件的名字就是全类名
    *
    *
    *
    */
   
   @Import({User.class, DBHelper.class})
   @Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
   public class MyConfig {
   }
   

4. @Conditional

   条件装配：满足Conditional指定的条件，则进行组件注入

   

   =====================测试条件装配==========================
   @Configuration(proxyBeanMethods = false) //告诉SpringBoot这是一个配置类 == 配置文件
   //@ConditionalOnBean(name = "tom")
   @ConditionalOnMissingBean(name = "tom")
   public class MyConfig {
   
   
       /**
        * Full: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对象
        * @return
        */
   
       @Bean //给容器中添加组件。以方法名作为组件的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 user01(){
           User zhangsan = new User("zhangsan", 18);
           //user组件依赖了Pet组件
           zhangsan.setPet(tomcatPet());
           return zhangsan;
       }
   
       @Bean("tom22")
       public Pet tomcatPet(){
           return new Pet("tomcat");
       }
   }
   
   public static void main(String[] args) {
           //1、返回我们IOC容器
           ConfigurableApplicationContext run = SpringApplication.run(MainApplication.class, args);
   
           //2、查看容器里面的组件
           String[] names = run.getBeanDefinitionNames();
           for (String name : names) {
               System.out.println(name);
           }
   
           boolean tom = run.containsBean("tom");
           System.out.println("容器中Tom组件："+tom);
   
           boolean user01 = run.containsBean("user01");
           System.out.println("容器中user01组件："+user01);
   
           boolean tom22 = run.containsBean("tom22");
           System.out.println("容器中tom22组件："+tom22);
   
   
       }
   

2.2 原生配置文件引入

1. @ImportResource

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

    <bean id="haha" class="com.atguigu.boot.bean.User">
        <property name="name" value="zhangsan"></property>
        <property name="age" value="18"></property>
    </bean>

    <bean id="hehe" class="com.atguigu.boot.bean.Pet">
        <property name="name" value="tomcat"></property>
    </bean>
</beans>

@ImportResource("classpath:beans.xml")
public class MyConfig {}

======================测试=================
        boolean haha = run.containsBean("haha");
        boolean hehe = run.containsBean("hehe");
        System.out.println("haha："+haha);//true
        System.out.println("hehe："+hehe);//true

2.3 配置绑定

如何使用Java读取到properties文件中的内容，并且把它封装到JavaBean中，以供随时使用；

public class getProperties {
     public static void main(String[] args) throws FileNotFoundException, IOException {
         Properties pps = new Properties();
         pps.load(new FileInputStream("a.properties"));
         Enumeration enum1 = pps.propertyNames();//得到配置文件的名字
         while(enum1.hasMoreElements()) {
             String strKey = (String) enum1.nextElement();
             String strValue = pps.getProperty(strKey);
             System.out.println(strKey + "=" + strValue);
             //封装到JavaBean。
         }
     }
 }

2.3.1 @ConfigurationProperties

/**
 * 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 +
                '}';
    }
}

2.3.3 @EnableConfigurationProperties + @ConfigurationProperties

2.3.4 @Component + @ConfigurationProperties

​

@EnableConfigurationProperties(Car.class)
//1、开启Car配置绑定功能
//2、把这个Car这个组件自动注册到容器中
public class MyConfig {
}

3. 自动配置原理入门

3.1 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{}

1. @SpringBootConfiguration

   @Configuration.代表当前是一个配置类

2. @ComponentScan

   指定扫描哪些组件，Spring注解。

3. @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
     

     

     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
     

     这是springboot会自动加载的组件

3.2 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。

3.3，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组件。但是如果用户自己配置了的话 以用户配置的优先

例如：

@Bean
	@ConditionalOnMissingBean
	public CharacterEncodingFilter characterEncodingFilter() {
    }

3.4 总结

1. SpringBoot启动时先加载所有的自动配置类 xxxxAutoConfiguration

2. 每个自动配置类按照条件进行生效（Conditonalxxxx），默认都会绑定配置文件中的值，xxxxProperties里面拿。xxxxProperties和配置文件进行了绑定

3. 生效了的配置类会给容器配置相应的组件

4. 只要容器中有这些组将，就相当于有了这些功能

5. 定制配置

   • a>用户自己配置Bean替换底层的组件

   • b>用户去看这个组件是获取的配置文件的什么值，自己去配置文件中修改

     xxxxAutoConfiguration —->对应的组件—->xxxxProperties里面拿值—–application.properties