SpringBoot系列（自动配置原理） SpringBoot系列：自动配置原理

本文主要了解三大模块知识点

SpringBoot配置文件到底能写什么？
SpringBoot配置文件怎么写？
自动配置原理

1、配置文件能写什么？
【SpringBoot系列（自动配置原理）】配置文件能配置的属性参照可以查看官方文档：https://docs.spring.io/spring-boot/docs/2.1.9.RELEASE/reference/html/common-application-properties.html
2、自动配置原理
1）、SpringBoot启动的时候加载主配置类，并且开启了自动配置功能@EnableAutoConfiguration
2）、@EnableAutoConfiguration的作用：
- 利用AutoConfigurationImportSelector给容器中导入一些组件
- 导入了哪些组件可以查看AutoConfigurationImportSelector.selectImports()方法
- 获取候选的配置：List configurations = getCandidateConfigurations(annotationMetadata, attributes);

SpringFactoriesLoader.loadFactoryNames 扫描所有jar包类路径下的：META-INF/spring.factories 把扫描到的这些文件的内容包装成properties对象从properties中获取到EnableAutoConfiguration.class类（类名）对应的值，然后把它们添加到容器中

将类路径下的META-INF/spring.factories里面配置的所有EnableAutoConfiguration的值加入到容器中

# 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.cloud.CloudServiceConnectorsAutoConfiguration,\ org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\ 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.ElasticsearchAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\ 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.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.jest.JestAutoConfiguration,\ org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\ org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\ org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\ 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.groovy.template.GroovyTemplateAutoConfiguration,\ 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.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.reactor.core.ReactorCoreAutoConfiguration,\ 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.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

每一个xxxAutoConfiguration类都是容器中的一个组件，都加入到容器中用来做自动化配置。
3）、每一个自动配置类进行自动配置功能
4）、以HttpEncodingAutoConfiguration为例

@Configuration @EnableConfigurationProperties(HttpProperties.class) @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET) @ConditionalOnClass(CharacterEncodingFilter.class) @ConditionalOnProperty(prefix = "spring.http.encoding", value = "https://www.it610.com/article/enabled", matchIfMissing = true) //判断配置文件中是否存在spring.http.encoding.enabled配置 public class HttpEncodingAutoConfiguration {// 已经和SpringBoot的配置文件映射了 private final HttpProperties.Encoding 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(HttpProperties properties) { this.properties = properties.getEncoding(); }@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 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; } // 省略 }

注解说明：

@Configuration ：表示这是一个配置类
@EnableConfigurationProperties(HttpProperties.class) ：启用指定类的ConfigurationProperties功能，将配置文件中的值和HttpProperties.class中的属性绑定起来
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET) ： Spring底层@Conditional注解，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回生效，判断当前应用是否是web应用，如果是则生效配置类
@ConditionalOnClass(CharacterEncodingFilter.class) ：判断当前项目有没有这个类，乱码解决的过滤器
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "https://www.it610.com/article/enabled", matchIfMissing = true) ：判断配置文件中是否存在spring.http.encoding.enabled配置

5）、所有在配置文件中能配置的属性都是在xxxProperties类中封装着
HttpProperties.class源码

@ConfigurationProperties(prefix = "spring.http")// 从配置文件中获取指定的值和bean的属性进行绑定 public class HttpProperties {/** * Whether logging of (potentially sensitive) request details at DEBUG and TRACE level * is allowed. */ private boolean logRequestDetails; /** * HTTP encoding properties. */ private final Encoding encoding = new Encoding(); public boolean isLogRequestDetails() { return this.logRequestDetails; }public void setLogRequestDetails(boolean logRequestDetails) { this.logRequestDetails = logRequestDetails; }public Encoding getEncoding() { return this.encoding; }/** * Configuration properties for http encoding. */ public static class Encoding {public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8; /** * Charset of HTTP requests and responses. Added to the "Content-Type" header if * not set explicitly. */ private Charset charset = DEFAULT_CHARSET; /** * Whether to force the encoding to the configured charset on HTTP requests and * responses. */ private Boolean force; /** * Whether to force the encoding to the configured charset on HTTP requests. * Defaults to true when "force" has not been specified. */ private Boolean forceRequest; /** * Whether to force the encoding to the configured charset on HTTP responses. */ private Boolean forceResponse; }}

3、@Conditional扩展
作用：必须是@Conditional指定的条件成立，才给容器添加组件，配置项里面的所有内容才会生效；

@Conditional扩展注解	作用（判断是否满足当前指定条件）
@ConditionalOnJava	系统的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	满足SpEL表达式指定
@ConditionalOnClass	系统中有指定的类
@ConditionalOnMissingClass	系统中没有指定的类
@ConditionalOnSingleCandidate	容器中只有一个指定的Bean或者这个Bean是首选Bean
@ConditionalOnProperty	系统中指定的属性是否有指定的值
@ConditionalOnResource	类路径下是否存在指定资源文件
@ConditionalOnWebApplication	当前是web环境
@ConditionalOnNotWebApplication	当前不是web环境
@ConditionalOnJndi	JNDI存在指定项