springBoot的自動注冊

整個springboot并沒有在spring的基礎(chǔ)上提供什么額外的功能。
springBoot的最大作用就是引入某些jar包后寓搬，自動為spring上下文環(huán)境生成某些特定功能的Bean，這樣就可以自動提供某些相關(guān)功能流酬。
本質(zhì)上若治，spring通過被標記了@Configuration的類提供一些提前生成好的Bean提供特別的功能峡眶，而用@Contional系列的注解限制生成的條件，通常就是@ConditionalOnClass和@ConditionalOnMissingBean注解的配合使用京革。前者確定某些功能需要的class已經(jīng)有了销睁，后者確定你沒有自己生成相關(guān)的bean，才提供默認的存崖。

spring-boot-autoconfigure

spring通過spring-boot-autoconfigure這個jar提供大量的自動注冊功能冻记。
springboot啟動的時候會掃描jar下是否有 META-INF/spring.factories 文件，這個文件中包含了你需要自動注冊的java類来惧。
比如spring-boot-autoconfigure這個jar下的META-INF/spring.factories文件提供了大量自動注冊的配置類:

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

# 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.OnClassCondition

# 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

# Failure analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer

# 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.JspTemplateAvailabilityProvider

由于springboot自己提供了這么多自動注冊類冗栗，我們自己也可能寫一些自動注冊類。為了確定他們直接的生效順序供搀。我可以使用@AutoConfigureBefore隅居，@AutoConfigureAfter，@AutoconfigureOrder 來確定某個自動注冊類的生效順序葛虐。作用類比@Order胎源。

注意：自動注冊的類需要放到特定的包中，避免被應(yīng)用的@ComponentScan掃描到屿脐。

自動注冊一般我們提供2個module：一個是autoconfigure jar包涕蚤，一個是starter jar包。
其中starter這種jar里面并沒有代碼的诵，是空的万栅。唯一的作用是將需要的各種jar寫入構(gòu)建文件，這樣引入此starter西疤，就不要再去關(guān)心相應(yīng)的其他jar了烦粒。
比如spring提供的 spring-boot-starter-data-redis 這個jar什么都沒有，只是pom文件引入了使用spring-data-redis中的功能需要的相關(guān)jar代赁。

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
        </dependency>
</dependencies>

而spring提供的spring-boot-autoconfigure里面有相關(guān)的類會根據(jù)相應(yīng)的條件生成redis功能需要的bean扰她，所以我們只需要加入springboot提供的spring-boot-starter-xxx 的jar就可以自動生成相應(yīng)功能的bean了。

image.png

@Configuration
@ConditionalOnClass({ JedisConnection.class, RedisOperations.class, Jedis.class })
@EnableConfigurationProperties(RedisProperties.class)
public class RedisAutoConfiguration {

    /**
     * Redis connection configuration.
     */
    @Configuration
    @ConditionalOnClass(GenericObjectPool.class)
    protected static class RedisConnectionConfiguration {
           ……略
    }

    /**
     * Standard Redis configuration.
     */
    @Configuration
    protected static class RedisConfiguration {
            ……略
    }

}

這個類里面有2個子類芭碍，一個RedisConfiguration徒役，RedisConnectionConfiguration。
先看簡單的豁跑，RedisConfiguration：

/**
     * Standard Redis configuration.
     */
    @Configuration
    protected static class RedisConfiguration {
        //當spring上下文中沒有name叫redisTemplate的bean就會自動生成RedisTemplate
        //當然前提是的上下文中已經(jīng)有RedisConnectionFactory了廉涕，否則自動注入失敗會報錯
        @Bean
        @ConditionalOnMissingBean(name = "redisTemplate")
        public RedisTemplate<Object, Object> redisTemplate(
                RedisConnectionFactory redisConnectionFactory)
                        throws UnknownHostException {
            RedisTemplate<Object, Object> template = new RedisTemplate<Object, Object>();
            template.setConnectionFactory(redisConnectionFactory);
            return template;
        }
         //同理當上下文中沒有類型為StringRedisTemplate的Bean就會自動生成StringRedisTemplate泻云。
        //同理需要注入RedisConnectionFactory
        @Bean
        @ConditionalOnMissingBean(StringRedisTemplate.class)
        public StringRedisTemplate stringRedisTemplate(
                RedisConnectionFactory redisConnectionFactory)
                        throws UnknownHostException {
            StringRedisTemplate template = new StringRedisTemplate();
            template.setConnectionFactory(redisConnectionFactory);
            return template;
        }

    }

所以這個類到底干嘛呢艇拍？就是為spring上下文生成一個RedisTemplate狐蜕，一個StringRedisTemp。好供用戶操作redis卸夕。
第二個類, RedisConnectionConfiguration：

    /**
     * Redis connection configuration.
     */
    @Configuration
    //這個條件是指需要commons-pool這個jar,因為jedis底層依賴此jar提供連接池的能力
    @ConditionalOnClass(GenericObjectPool.class)
    protected static class RedisConnectionConfiguration {

        private final RedisProperties properties;

        private final RedisSentinelConfiguration sentinelConfiguration;

        private final RedisClusterConfiguration clusterConfiguration;
        //注入RedisProperties层释，就是我們autoconfigure jar里面提供的類
        //另外2個是RedisSentinelConfiguration，RedisClusterConfiguration快集。但這2個bean并
        //不一定有贡羔，所以，使用ObjectProvider#getIfAvailable
        public RedisConnectionConfiguration(RedisProperties properties,
                ObjectProvider<RedisSentinelConfiguration> sentinelConfigurationProvider,
                ObjectProvider<RedisClusterConfiguration> clusterConfigurationProvider) {
            this.properties = properties;
            this.sentinelConfiguration = sentinelConfigurationProvider.getIfAvailable();
            this.clusterConfiguration = clusterConfigurationProvider.getIfAvailable();
        }
        //如果沒有RedisConnectionFactory的bean,生成JedisConnectionFactory
        //同時為JedisConnectionFactory注入RedisProperties中的基本屬性
        @Bean
        @ConditionalOnMissingBean(RedisConnectionFactory.class)
        public JedisConnectionFactory redisConnectionFactory()
                throws UnknownHostException {
            return applyProperties(createJedisConnectionFactory());
        }
        //為JedisConnectionFactory注入host个初，port乖寒，password，database院溺，timeout等基本屬性
        protected final JedisConnectionFactory applyProperties(
                JedisConnectionFactory factory) {
            factory.setHostName(this.properties.getHost());
            factory.setPort(this.properties.getPort());
            if (this.properties.getPassword() != null) {
                factory.setPassword(this.properties.getPassword());
            }
            factory.setDatabase(this.properties.getDatabase());
            if (this.properties.getTimeout() > 0) {
                factory.setTimeout(this.properties.getTimeout());
            }
            return factory;
        }
        //下面幾個方法的作用類似楣嘁，就是檢查spring上下文中是否已經(jīng)有sentinel，cluster的配置
        //bean（從構(gòu)造函數(shù)注入的剛才）珍逸，如果有逐虚，就用已有的，沒有谆膳，就用
        //從RedisProperties中寫入的屬性生成叭爱。
        protected final RedisSentinelConfiguration getSentinelConfig() {
            if (this.sentinelConfiguration != null) {
                return this.sentinelConfiguration;
            }
            Sentinel sentinelProperties = this.properties.getSentinel();
            if (sentinelProperties != null) {
                RedisSentinelConfiguration config = new RedisSentinelConfiguration();
                config.master(sentinelProperties.getMaster());
                config.setSentinels(createSentinels(sentinelProperties));
                return config;
            }
            return null;
        }
               
        /**
         * Create a {@link RedisClusterConfiguration} if necessary.
         * @return {@literal null} if no cluster settings are set.
         */
        protected final RedisClusterConfiguration getClusterConfiguration() {
            if (this.clusterConfiguration != null) {
                return this.clusterConfiguration;
            }
            if (this.properties.getCluster() == null) {
                return null;
            }
            Cluster clusterProperties = this.properties.getCluster();
            RedisClusterConfiguration config = new RedisClusterConfiguration(
                    clusterProperties.getNodes());

            if (clusterProperties.getMaxRedirects() != null) {
                config.setMaxRedirects(clusterProperties.getMaxRedirects());
            }
            return config;
        }

        private List<RedisNode> createSentinels(Sentinel sentinel) {
            List<RedisNode> nodes = new ArrayList<RedisNode>();
            for (String node : StringUtils
                    .commaDelimitedListToStringArray(sentinel.getNodes())) {
                try {
                    String[] parts = StringUtils.split(node, ":");
                    Assert.state(parts.length == 2, "Must be defined as 'host:port'");
                    nodes.add(new RedisNode(parts[0], Integer.valueOf(parts[1])));
                }
                catch (RuntimeException ex) {
                    throw new IllegalStateException(
                            "Invalid redis sentinel " + "property '" + node + "'", ex);
                }
            }
            return nodes;
        }

        private JedisConnectionFactory createJedisConnectionFactory() {
            JedisPoolConfig poolConfig = this.properties.getPool() != null
                    ? jedisPoolConfig() : new JedisPoolConfig();

            if (getSentinelConfig() != null) {
                return new JedisConnectionFactory(getSentinelConfig(), poolConfig);
            }
            if (getClusterConfiguration() != null) {
                return new JedisConnectionFactory(getClusterConfiguration(), poolConfig);
            }
            return new JedisConnectionFactory(poolConfig);
        }

        private JedisPoolConfig jedisPoolConfig() {
            JedisPoolConfig config = new JedisPoolConfig();
            RedisProperties.Pool props = this.properties.getPool();
            config.setMaxTotal(props.getMaxActive());
            config.setMaxIdle(props.getMaxIdle());
            config.setMinIdle(props.getMinIdle());
            config.setMaxWaitMillis(props.getMaxWait());
            return config;
        }

    }

所以RedisConnectionConfiguration的主要作用就是在沒有RedisConnectionFactory的時候，通過RedisProperties提供的屬性漱病，生成前文提到的RedisConnectionFactory（為RedisTemplate使用)