SpringBoot系列：自動配置原理

本文主要了解三大模塊知識點

  • SpringBoot配置文件到底能寫什么？
  • SpringBoot配置文件怎么寫？
  • 自動配置原理

1、配置文件能寫什么？

配置文件能配置的屬性參照可以查看官方文檔：https://docs.spring.io/spring-boot/docs/2.1.9.RELEASE/reference/html/common-application-properties.html

2、自動配置原理

1）、SpringBoot啟動的時候加載主配置類，并且開啟了自動配置功能@EnableAutoConfiguration
2）、@EnableAutoConfiguration的作用：
- 利用AutoConfigurationImportSelector給容器中導(dǎo)入一些組件
- 導(dǎo)入了哪些組件可以查看AutoConfigurationImportSelector.selectImports()方法
- 獲取候選的配置：List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);

SpringFactoriesLoader.loadFactoryNames
掃描所有jar包類路徑下的：META-INF/spring.factories
把掃描到的這些文件的內(nèi)容包裝成properties對象
從properties中獲取到EnableAutoConfiguration.class類（類名）對應(yīng)的值，然后把它們添加到容器中

將類路徑下的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

每一個xxxAutoConfiguration類都是容器中的一個組件，都加入到容器中用來做自動化配置。
3）、每一個自動配置類進(jìn)行自動配置功能
4）、以HttpEncodingAutoConfiguration為例

@Configuration  
@EnableConfigurationProperties(HttpProperties.class) 
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)  
@ConditionalOnClass(CharacterEncodingFilter.class) 
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true) //判斷配置文件中是否存在spring.http.encoding.enabled配置
public class HttpEncodingAutoConfiguration {

  // 已經(jīng)和SpringBoot的配置文件映射了
    private final HttpProperties.Encoding properties;
 
  //只有一個有參構(gòu)造器的情況下，參數(shù)的值就會從容器中拿
    public HttpEncodingAutoConfiguration(HttpProperties properties) {
        this.properties = properties.getEncoding();
    }

    @Bean  //給容器中添加一個組件，這個組件的某些值需要從properties中獲取
    @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
}

注解說明：

  • @Configuration ： 表示這是一個配置類
  • @EnableConfigurationProperties(HttpProperties.class) ：啟用指定類的ConfigurationProperties功能，將配置文件中的值和HttpProperties.class中的屬性綁定起來
  • @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET) ： Spring底層@Conditional注解，根據(jù)不同的條件，如果滿足指定的條件，整個配置類里面的配置就回生效，判斷當(dāng)前應(yīng)用是否是web應(yīng)用，如果是則生效配置類
  • @ConditionalOnClass(CharacterEncodingFilter.class) ：判斷當(dāng)前項目有沒有這個類，亂碼解決的過濾器
  • @ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true) ：判斷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屬性都是在xxxProperties類中封裝著
HttpProperties.class源碼

@ConfigurationProperties(prefix = "spring.http")  // 從配置文件中獲取指定的值和bean的屬性進(jìn)行綁定
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擴(kuò)展

作用：必須是@Conditional指定的條件成立，才給容器添加組件，配置項里面的所有內(nèi)容才會生效；

@Conditional擴(kuò)展注解 作用（判斷是否滿足當(dāng)前指定條件）
@ConditionalOnJava 系統(tǒng)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(dá)式指定
@ConditionalOnClass 系統(tǒng)中有指定的類
@ConditionalOnMissingClass 系統(tǒng)中沒有指定的類
@ConditionalOnSingleCandidate 容器中只有一個指定的Bean或者這個Bean是首選Bean
@ConditionalOnProperty 系統(tǒng)中指定的屬性是否有指定的值
@ConditionalOnResource 類路徑下是否存在指定資源文件
@ConditionalOnWebApplication 當(dāng)前是web環(huán)境
@ConditionalOnNotWebApplication 當(dāng)前不是web環(huán)境
@ConditionalOnJndi JNDI存在指定項

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