3.了解Spring Boot2自动配置原理（下）-阿里云开发者社区

1、@Component + @ConfigurationProperties

@ConfigurationProperties:SpringBoot配置文件中前缀为prefix的信息和类中相关属性一一绑定

/**
 * 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")// SpringBoot配置文件中前缀为prefix的信息 和类中相关属性一一绑定.
public class Car {
    private String brand;
    private Integer price;
    public Car(String brand, Integer price) {
        this.brand = brand;
        this.price = price;
    }
    public Car() {
    }
    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、@EnableConfigurationProperties + @ConfigurationProperties

@ConfigurationProperties(prefix = "mycar")// SpringBoot配置文件中前缀为prefix的信息 和类中相关属性一一绑定.
public class Car {
    private String brand;
    private Integer price;
    .....
}
####################################MyConfig#####################
@EnableConfigurationProperties(Car.class)
/**
 * 1.开启Car配置绑定功能
 * 2.把这个car组件自动注册到容器中
 */
public class MyConfig {
  ......
}

3、自动配置原理入门

3.1、@SpringBootApplication

@SpringBootApplication:引导加载自动配置类

底层代码:

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

1、@SpringBootConfiguration

底层原理是:@Configuration:代表当前是一个配置类

2、@ComponentScan

作用:进行包扫描

3、@EnableAutoConfiguration

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

@AutoConfigurationPackage

作用: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 {}
//作用:
//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(一共127个,如下图)
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
以下是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

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

但按照条件装配规则（@Conditional），最终会按需配置。

如:没有使用AOP时,AopAutoConfiguration中的配置是报红的,没有使用批量处理时,批处理里面的配置不会进行加载.(底层实现大量使用@Conditional)

底层代码举例分析:

#######################################AopAutoConfiguration##############################
@Configuration(proxyBeanMethods = false)//开启对象的代理
@ConditionalOnProperty(prefix = "spring.aop", name = "auto", havingValue = "true", matchIfMissing = true)//判断是否存在以spring.aop为前缀,name为auto,值为true的配置,如果存在,则下面的生效;matchIfMissing=true:表示即使你没有配,也认为你配置了.  默认是开启的.
public class AopAutoConfiguration {
    @Configuration(proxyBeanMethods = false)
  @ConditionalOnClass(Advice.class)//判断是否存在Advice类,如果不存在则下面类中所有行为将不会执行.(由于我们没有导入Aop相关场景,所有无该类.)
  static class AspectJAutoProxyingConfiguration {
        ...
    }
    @Configuration(proxyBeanMethods = false)
  @ConditionalOnMissingClass("org.aspectj.weaver.Advice")//如果没有则下面的生效
  @ConditionalOnProperty(prefix = "spring.aop", name = "proxy-target-class", havingValue = "true",
      matchIfMissing = true)//...
  static class ClassProxyingConfiguration {
        ...
    }
}
############################ CacheAutoConfiguration(自动缓存) #######################
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(CacheManager.class)// 可以通过run.getBean()进行验证是否容器中有..验证后没有,则类中一系列操作配置都是无效的...多没有进行配置.
@ConditionalOnBean(CacheAspectSupport.class)
@ConditionalOnMissingBean(value = CacheManager.class, name = "cacheResolver")
@EnableConfigurationProperties(CacheProperties.class)
@AutoConfigureAfter({ CouchbaseDataAutoConfiguration.class, HazelcastAutoConfiguration.class,
    HibernateJpaAutoConfiguration.class, RedisAutoConfiguration.class })
@Import({ CacheConfigurationImportSelector.class, CacheManagerEntityManagerFactoryDependsOnPostProcessor.class })
public class CacheAutoConfiguration {
   // ...一系列配置...
}
##################################DispatcherServletAutoConfiguration#####################
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)//指定配置顺序
@Configuration(proxyBeanMethods = false)//开启方法的代理
@ConditionalOnWebApplication(type = Type.SERVLET)//判断是不是一个原生的Servlet类型的Web应用.
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)//在ServletWebServerFactoryAutoConfiguration配置之后执行.
public class DispatcherServletAutoConfiguration {
    @Configuration(proxyBeanMethods = false)
  @Conditional(DefaultDispatcherServletCondition.class)
  @ConditionalOnClass(ServletRegistration.class)
  @EnableConfigurationProperties(WebMvcProperties.class)//1.开启WebMvcProperties上配置文件的配置绑定功能;  2.将该组件添加到容器中.
    //给容器中添加组件:dispatcherservlet
  protected static class DispatcherServletConfiguration {
        @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
    public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
            //创建一个DispatcherServlet,并设置相关属性.然后将该组件起名加到容器中; 之前是我们进行手动配置的,现在SpringBoot底层给我们进行了配置.
      DispatcherServlet dispatcherServlet = new DispatcherServlet();
      dispatcherServlet.setDispatchOptionsRequest(...);
      dispatcherServlet.setDispatchTraceRequest(...);
      dispatcherServlet.setThrowExceptionIfNoHandlerFound(...);
      dispatcherServlet.setPublishEvents(...);
      dispatcherServlet.setEnableLoggingRequestDetails(...);
      return dispatcherServlet;
    }
        //给容器中添加文件上传解析器multipartResolver
    @Bean
    @ConditionalOnBean(MultipartResolver.class)//判断容器中是否有这个类型的组件
    @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) {
            //1.给@Bean标注的方法传入了对象参数,这个参数的值会从容器中找.然后以方法名为组件名称再次存入到容器中;    2.这样做可以防止有些用户配置的文件上传解析器不符合规范.
      return resolver;
    }
    }
    //......
}
###########################################HttpEncodingAutoConfiguration#################
@Configuration(proxyBeanMethods = false)//关闭方法的代理
@EnableConfigurationProperties(ServerProperties.class)//进行类和配置文件的绑定,并加载到容器
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)//判断是不是原生的Servlet类型 Web应用
@ConditionalOnClass(CharacterEncodingFilter.class)//判断是不是
@ConditionalOnProperty(prefix = "server.servlet.encoding", value = "enabled", matchIfMissing = true)//判断配置的server.servlet.encoding是否是enabled;即使你没有配置也认为配置了.
public class HttpEncodingAutoConfiguration {//HTTp编码自动配置.
    //...
    //配置编码过滤器
    @Bean
  @ConditionalOnMissingBean//如果容器中没有该组件,就进行配置;如果有则不再进行配置.
  public CharacterEncodingFilter characterEncodingFilter() {
    CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
    filter.setEncoding(this.properties.getCharset().name());
    filter.setForceRequestEncoding(this.properties.shouldForce(Encoding.Type.REQUEST));
    filter.setForceResponseEncoding(this.properties.shouldForce(Encoding.Type.RESPONSE));
    return filter;
  }
      //...
}
总结: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,则以用户的优先.

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(@Conditional )进行生效，默认都会绑定配置文件指定的值。(xxxProperties类和配置文件进行了绑定,用于在组件注册前进行类对象的属性赋值.)

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

用户直接在配置类中使用@Bean替换底层的组件

用户去看这个组件的底层是获取的配置文件什么值(或者查看官方文档),然后去配置文件里修改。

历程:xxxxxAutoConfiguration —> 组件 —> xxxxProperties里面拿值 ----> application.properties

3.3、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或自己分析: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；

…

4、开发小技巧

4.1、Lombok

简化JavaBean开发

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
idea中搜索安装lombok插件
===============================简化JavaBean开发===================================
@NoArgsConstructor//无参
@AllArgsConstructor//有参
@Data//getter/setter
@ToString//toString
@EqualsAndHashCode
public class User {
    private String name;
    private Integer age;
    private Pet pet;
    public User(String name, Integer age) {//自定义构造方法
        this.name = name;
        this.age = age;
    }
}
================================简化日志开发===================================
@Slf4j
@RestController
public class HelloController {
    @RequestMapping("/hello")
    public String handle01(@RequestParam("name") String name){
        log.info("请求进来了....");
        return "Hello, Spring Boot 2!"+"你好："+name;
    }
}

4.2、dev-tools

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>

项目或者页面修改以后：Ctrl+F9,用于快速重启项目.

4.3、Spring Initailizr（项目初始化向导）

1、选择我们需要的开发场景

File->new Project ->Spring Spring Initailizr->Next 填写项目的信息,完成点击NEXT

2.选择项目需要的配置信息

选择Spring Boot 版本信息,目前我们开发Web应用,Developer Tools勾选:Spring Boot DevTools,Lombok,Spring Configuration Processor; Web中勾选Spring Web;

SQL中勾选MyBatis Framework, Mysql Driver.…

优点:

自动依赖引入

自动创建项目结构

自动编写好主配置类

3.了解Spring Boot2自动配置原理（下）