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SpringBoot自動組裝原理的知識點有哪些

王林
王林轉載
2023-05-15 08:01:251083瀏覽

SpringBoot自動組裝原理

自動組裝原理

pom.xml

  • spring-boot-dependencies:核心依賴父工程!

  • 我們在寫或寫入一些springboot依賴的時候,不需要指定版本,就因為有這些版本倉庫

啟動器

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

啟動器:說白了就是SpringBoot的啟動場景

例如:spring-boot-starter-web,他就會幫我們自動導入web環境所有的依賴!

SpringBoot會將所有的功能場景,都變成一個個的啟動器

我們要使用什麼功能,就只需要找到對用的啟動器就可以了starter

主程式

@SpringBootApplication // 标注这个类是一个Springboot的应用
public class SpringbootHelloworldApplication {

    public static void main(String[] args) {
        // 将SpringBoot应用启动
        SpringApplication.run(SpringbootHelloworldApplication.class, args);
    }

}

註解

原理:

SpringBoot啟動的時候載入主配置類,開啟了自動配置功能@EnableAutoConfiguration

@SpringBootApplication  // 加载主配置类
	@EnableAutoConfiguration// 开启了自动配置功能 
		@Import({AutoConfigurationImportSelector.class})
			AutoConfigurationImportSelector // 这个新版本的,旧版本是 EnableAutoConfigurationImportSelector
                	- 利用AutoConfigurationImportSelector给容器中导入一些组件
			- 可以查看selectImports()方法的内容;
			- List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);// 获取候选的配置

                        protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
                            List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
                            Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");
                            return configurations;
                        }
                        SpringFactoriesLoader.loadFactoryNames()
                        扫描所有jar包类路径下  META-INF/spring.factories
                        把扫描到的这些文件的内容包装成List对象
                        从List中获取到EnableAutoConfiguration.class类(类名)对应的值,然后把他们添加在容器中

將類別路徑下META-INF/spring.factories 裡面配置的所有EnableAutoConfiguration的值加入到了容器中

# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer

# Auto Configuration Import Listeners
org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener

# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition

# 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.h3.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.oauth3.client.servlet.OAuth3ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth3.client.reactive.ReactiveOAuth3ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth3.resource.servlet.OAuth3ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth3.resource.reactive.ReactiveOAuth3ResourceServerAutoConfiguration,\
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

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.data.redis.RedisUrlSyntaxFailureAnalyzer,\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer

# Template availability providers
org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

每一個這樣的xxxAutoConfiguration類別都是容器中的一個元件,都加入到容器中;用他們來做自動配置;

每一個自動配置類別進行自動配置功能;

以HttpEncodingAutoConfiguration(Http編碼自動配置)為例解釋自動配置原理;

@Configuration   //表示这是一个配置类,以前编写的配置文件一样,也可以给容器中添加组件
@EnableConfigurationProperties(ServerProperties.class)  //启动指定类的ConfigurationProperties功能;将配置文件中对应的值和 ServerProperties 绑定起来;并把 ServerProperties 加入到ioc容器中

@ConditionalOnWebApplication //Spring底层@Conditional注解(Spring注解版),根据不同的条件,如果满足指定的条件,整个配置类里面的配置就会生效;    判断当前应用是否是web应用,如果是,当前配置类生效

@ConditionalOnClass(CharacterEncodingFilter.class)  //判断当前项目有没有这个类CharacterEncodingFilter;SpringMVC中进行乱码解决的过滤器;

@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)  //判断配置文件中是否存在某个配置  spring.http.encoding.enabled;如果不存在,判断也是成立的
//即使我们配置文件中不配置pring.http.encoding.enabled=true,也是默认生效的;
public class HttpEncodingAutoConfiguration {
  
  	//他已经和SpringBoot的配置文件映射了
  	private final HttpEncodingProperties properties;
  
   //只有一个有参构造器的情况下,参数的值就会从容器中拿
  	public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
		this.properties = properties;
	}
  
    @Bean   //给容器中添加一个组件,这个组件的某些值需要从properties中获取
	@ConditionalOnMissingBean(CharacterEncodingFilter.class) //判断容器没有这个组件?
	public CharacterEncodingFilter characterEncodingFilter() {
		CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
		filter.setEncoding(this.properties.getCharset().name());
		filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
		filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
		return filter;
	}

根據目前不同的條件判斷,決定這個配置類別是否生效?

一但這個配置類別生效;這個配置類別就會在容器中加入各種元件;這些元件的屬性是從對應的properties類別中取得的,這些類別裡面的每一個屬性又是和設定檔綁定的;

5)、所有在設定檔中能配置的屬性都是在xxxxProperties類別中封裝者';設定檔能配置什麼就可以參考某個功能對應的這個屬性類

@ConfigurationProperties(prefix = "spring.http.encoding")  //从配置文件中获取指定的值和bean的属性进行绑定
public class HttpEncodingProperties {

   public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");

精華:

1)、SpringBoot启动会加载大量的自动配置类

2)、我们看我们需要的功能有没有SpringBoot默认写好的自动配置类;

3)、我们再来看这个自动配置类中到底配置了哪些组件;(只要我们要用的组件有,我们就不需要再来配置了)

4)、给容器中自动配置类添加组件的时候,会从properties类中获取某些属性。我们就可以在配置文件中指定这些属性的值;

xxxxAutoConfigurartion:自動配置類別;

在容器中新增元件

xxxxProperties:封裝設定檔中相關屬性;

細節

@Conditional派生註解(Spring註解版原生的@Conditional作用)

作用:必須是@Conditional指定的條件成立,才給容器中加入元件,配置配裡面的所有內容才生效;

@Conditional擴充註解作用(判斷是否符合目前指定條件)
@ConditionalOnJava 系統的java版本是否符合要求
@ConditionalOnBean 容器中存在指定Bean;
@ConditionalOnMissingBean 容器中不存在指定Bean;
@ConditionalOnExpression 滿足SpEL表達式指定
@ConditionalOnClass 系統中有指定的類別
@ConditionalOnMissingClass 系統中沒有指定的類別
@ConditionalOnSingleCandidate 容器中只有一個指定的Bean,或是這個Bean是首選Bean @ConditionalOnProperty 系統中指定的屬性是否有指定的值
@ConditionalOnResource 類別路徑下是否存在指定資源檔案
@ConditionalOnWebApplication 目前是web環境
@ConditionalOnNotWebApplication 目前不是web環境
@ConditionalOnJndi JNDI存在指定項目

自動配置類別必須在一定的條件下才能生效;

我們怎麼知道哪些自動設定類別生效;

我們可以透過啟用debug=true屬性;來讓控制台列印自動配置報告,這樣我們就可以很方便的知道哪些自動配置類別生效

結論:SpringBoot所有的自動配置都是在啟動的時候掃描並載入:spring.factories所有的自動配置類別都在這裡面,但是不一定生效,要判斷條件是否成立,只要導入了對應的starter,就有對應的啟動器了,有了啟動器,我們自動配置就會生效,然後就配置成功了!

  1. SpringBoot在啟動的時候,從類別路徑下/META-INF/spring.factories 取得指定的值

  2. 將這些自動配置的類別導入容器,自動配置就會生效,幫我們進行自動配置

  3. 以前我們需要自動配置的東西,現在SpringBoot幫我們做了

  4. 之前我們需要自動配置的東西,現在SpringBoot幫我們做了

  5. 整合JavaEE,解決方案和自動配置的東西都在spring-boot-autoconfigure-2.4.4.jar這個包下面

  6. 他會把所有需要導入的元件,以類別名稱的方式返回,這些元件就會被添加到Spring容器中

  7. #容器中也會存在非常多XXXAutoConfiguration的檔案@Bean ,就是這些類別給容器中導入了這個場景需要的所有元件,並自動配置@Configuration

有了自動配置類,免去了我們手動編寫設定檔的工作!

  • 談談你對SpringBoot的理解

  • #自動組裝

    • SpringApplication run
    • #1、推斷應用程式的類型是普通的項目還是web項目

    • 2、尋找並載入所有可用初始化器,設定到initializers屬性中

    • 3、找出所有的應用程式監聽器,設定到listeners屬性中

      ######4、推斷並設定main方法的定義類,找到運行的主類###
    • SpringApplication主要做了四件事

#啟動原則SpringApplication.run(主程式類別) new SpringApplication(主程式類別)

  • 判斷是否web應用

  • 載入並儲存所有ApplicationContextInitializer(META-INF/spring.factories),

  • 載入並儲存所有ApplicationListener

  • 取得到主程式類別– run()

  • 回呼所有的SpringApplicationRunListener(META-INF/ spring.factories)的starting

  • 取得ApplicationArguments

  • 準備環境&回呼所有監聽器( SpringApplicationRunListener )的environmentPrepared

    #列印banner資訊
  • 建立ioc容器物件( – AnnotationConfigEmbeddedWebApplicationContext(web環境容器) – AnnotationConfigApplicationContext(普通環境容器)
  • #自動組裝

  • Spring Boot啟動掃描所有jar套件的META-INF/spring.factories中配置的EnableAutoConfiguration元件

  • #spring- boot-autoconfigure.jar\META-INF\spring.factories有啟動時需要載入的EnableAutoConfiguration元件設定

設定檔中使用debug=true可以觀看到目前啟用的自動設定的資訊############自動配置會為容器中加入大量元件#############Spring Boot在做任何功能都需要從容器中取得這個功能的元件############Spring Boot 總是遵循一個標準;容器中有我們自己配置的元件就用我們配置的,沒有就用自動配置預設註冊進來的元件###### ###

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