What are the knowledge points of SpringBoot automatic assembly principle?

SpringBoot automatic assembly principle

Automatic assembly principle

pom.xml

• spring-boot-dependencies: The core dependencies are in the parent project!

• When we write or write some springboot dependencies, we do not need to specify the version, just because there are these version warehouses

Starter

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

Launcher: To put it bluntly, it is the startup scenario of SpringBoot

For example: spring-boot-starter-web, it will help us automatically import all the dependencies of the web environment!

SpringBoot will turn all functional scenarios into starters

What functions we want to use, we only need to find the right starter

Main program

@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);
    }

}

Note

Principle:

Loads the main configuration class when SpringBoot starts, and turns on the automatic configuration function @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

Add all EnableAutoConfiguration values ​​configured in META-INF/spring.factories under the class path to the container

# 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

Each such xxxAutoConfiguration class is a component in the container and is added to the container; use They do automatic configuration;

Each automatic configuration class performs automatic configuration functions;

Take HttpEncodingAutoConfiguration (Http encoding automatic configuration) as an example to explain the principle of automatic configuration;

@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;
	}

Based on different current conditions, determine whether this configuration class will take effect?

Once this configuration class takes effect; this configuration class will add various components to the container; the properties of these components are obtained from the corresponding properties classes, and each property in these classes is the same as The configuration file is bound;

5), all properties that can be configured in the configuration file are encapsulated in the xxxxProperties class; what can be configured in the configuration file can refer to the property class corresponding to a certain function

@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");

Essence:

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: Automatic configuration class;

Add components to the container

xxxxProperties: Encapsulate related properties in the configuration file;

Details

@Conditional derived annotation (Spring annotation version’s native @Conditional function)

Function: The condition specified by @Conditional must be true before adding components to the container and configuring All contents inside will take effect;

@Conditional extended annotation function (to determine whether the current specified conditions are met)
@ConditionalOnJava Whether the java version of the system meets the requirements
@ConditionalOnBean The specified Bean exists in the container;
@ConditionalOnMissingBean The specified Bean does not exist in the container;
@ConditionalOnExpression satisfies the SpEL expression specification
@ConditionalOnClass There is a specified class in the system
@ConditionalOnMissingClass There is no specified class in the system
@ConditionalOnSingleCandidate container There is only one specified Bean in the system, or this Bean is the preferred Bean @ConditionalOnProperty Whether the specified property in the system has the specified value
@ConditionalOnResource Whether the specified resource file exists under the class path
@ConditionalOnWebApplication The current web environment
@ConditionalOnNotWebApplication is not currently a web environment
@ConditionalOnJndi JNDI has specified items

Automatic configuration classes must take effect under certain conditions;

How do we know which automatic configuration classes take effect;

We can enable the debug=true attribute; to let the console print an automatic configuration report, so that we can easily know which automatic configuration classes are in effect

Conclusion: All automatic configurations of SpringBoot are Scan and load at startup: all the automatic configuration classes of spring.factories are here, but they may not take effect. To determine whether the conditions are true, as long as the corresponding starter is imported, there will be a corresponding starter. With startup The server, our automatic configuration will take effect, and then the configuration is successful!

1. When SpringBoot starts, it obtains the specified value from /META-INF/spring.factories on the classpath

2. Configure these automatically The class is imported into the container, and the automatic configuration will take effect, helping us with automatic configuration

3. We used to need to automatically configure things, but now SpringBoot does it for us

4. Integration of JavaEE, solutions and automatic configuration are all under the spring-boot-autoconfigure-2.4.4.jar package

5. It will include all components that need to be imported , returned in the form of class names, these components will be added to the Spring container

6. There will also be many XXXAutoConfiguration files @Bean in the container. It is these classes that are imported into the container. All the components needed for this scenario are included and automatically configured @Configuration

7. With the automatic configuration class, we save us the work of manually writing configuration files!

Talk about your understanding of SpringBoot

• Auto-assembly

• SpringApplication run

• 1. Infer whether the application type is an ordinary project or a web project

• 2. Find and load all available initializers and set them to initializers Properties

• 3. Find all application listeners and set them to the listeners property

• 4. Infer and set the main method Define the class and find the main class to run

• SpringApplication mainly does four things

Startup principle SpringApplication.run(main program class) new SpringApplication(main program class)

• Determine whether the web application

• Load and save all ApplicationContextInitializer (META-INF/spring.factories),

• Load and save all ApplicationListener

• Get the main program class – run()

• Call back all SpringApplicationRunListener (META-INF/ spring.factories) starting

• Get ApplicationArguments

• Prepare environment & callback environmentPrepared

of all listeners (SpringApplicationRunListener)

• Print banner information

• Create ioc container object (--AnnotationConfigEmbeddedWebApplicationContext (web environment container)--AnnotationConfigApplicationContext (common environment container)

Automatic assembly

• Spring Boot starts scanning the EnableAutoConfiguration component configured in META-INF/spring.factories of all jar packages

• ##spring- boot-autoconfigure.jar\META-INF\spring.factories has the EnableAutoConfiguration component configuration that needs to be loaded at startup.

• Use debug=true in the configuration file to view the currently enabled automatic configuration. Information

• Automatic configuration will add a large number of components to the container

• When Spring Boot does any function, it needs to obtain the components of this function from the container.

• Spring Boot always follows a standard; if there are components configured by ourselves in the container, we will use them. If not, we will use the components registered by default with automatic configuration

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