SpringBoot的自动配置原理

一、入口

上篇注解@SpringBootApplication简单分析，说到了@SpringBootApplication注解的内部结构，

其中@EnableAutoConfiguration利用EnableAutoConfigurationImportSelector.selectImports()给容器list中导入spring-boot-autoconfigure包下的多个配置类，根据包下的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.cloud.CloudAutoConfiguration,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.CassandraRepositoriesAutoConfiguration,org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,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.jpa.JpaRepositoriesAutoConfiguration,org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,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.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.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.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.flyway.FlywayAutoConfiguration,org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,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.mobile.DeviceResolverAutoConfiguration,org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,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.DispatcherServletAutoConfiguration,org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

这些Springboot提供的配置类就是自动配置的关键。下面找其中一个配置进一步分析。

二、HttpEncodingAutoConfiguration

@Configuration //表示这是一个配置类
@EnableConfigurationProperties(HttpEncodingProperties.class) //启动指定类的ConfigurationProperties功能；将配置文件中对应的值和HttpEncodingProperties绑定起来；并把HttpEncodingProperties加入到ioc容器中；加粗的就是该配置属性的封装类，我们可以根据这个类的字段知道支持配置哪些属性。

@ConditionalOnWebApplication // 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;

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;
}

这里有两点值得我们留意：

1.配置文件属性那么多，支持哪些？我们可以通过研究对应配置类的配置文件封装类如HttpEncodingProperties的XXXProperties类；

2.spring-boot-autoconfigure包下的那么多个配置类，ye也不是所以都加载，会根据条件，如@ConditionalOnWebApplication等等@ConditionalXXX条件注解。

三、HttpEncodingProperties

@ConfigurationProperties(prefix = "spring.http")
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;

        /**
         * Locale in which to encode mapping.
         */
        private Map<Locale, Charset> mapping;

        public Charset getCharset() {
            return this.charset;
        }

        public void setCharset(Charset charset) {
            this.charset = charset;
        }

        public boolean isForce() {
            return Boolean.TRUE.equals(this.force);
        }

        public void setForce(boolean force) {
            this.force = force;
        }

        public boolean isForceRequest() {
            return Boolean.TRUE.equals(this.forceRequest);
        }

        public void setForceRequest(boolean forceRequest) {
            this.forceRequest = forceRequest;
        }

        public boolean isForceResponse() {
            return Boolean.TRUE.equals(this.forceResponse);
        }

        public void setForceResponse(boolean forceResponse) {
            this.forceResponse = forceResponse;
        }

        public Map<Locale, Charset> getMapping() {
            return this.mapping;
        }

        public void setMapping(Map<Locale, Charset> mapping) {
            this.mapping = mapping;
        }

        public boolean shouldForce(Type type) {
            Boolean force = (type != Type.REQUEST) ? this.forceResponse
                    : this.forceRequest;
            if (force == null) {
                force = this.force;
            }
            if (force == null) {
                force = (type == Type.REQUEST);
            }
            return force;
        }

        public enum Type {

            REQUEST, RESPONSE

        }

    }

}

原文地址：https://www.cnblogs.com/Oven1993/p/10753985.html