SpringBoot自動配置的實現原理

以前一直在用SpringBoot框架，一直感受SpringBoot框架自動配置的功能很強大，可是並無明白它是怎麼實現自動配置的，如今有空研究了一下，大概明白了SpringBoot框架是怎麼實現自動配置的功能，咱們編寫一個最簡單的自動配置功能，大概的總結一下.

一,配置屬性類

其實就是值對象注入的方式去配置一些Spring經常使用的配置，咱們編寫一個最簡單的配置對象。

@ConfigurationProperties(prefix = "hello")
//@Component //若是這裏添加了註解那麼在自動配置類的時候就不用添加@enableConfigurationProperties(HelloProperties.class)註解.
public class HelloProperties {

    private String msg="default";//如今咱們在配置文件寫hello.msg=world,由於簡單就再也不展現;若是那麼默認爲default.

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

這是一個簡單的屬性值對象，那麼至關於寫死的字段就是SpringBoot爲咱們自動配置的配置，那麼咱們不少時候能夠本身在application.properties中修改某些配置就是這樣的道理，咱們不設置就是默認的，設置了就是咱們設置的屬性。

 

二,自動配置類

上面已經構建了咱們簡單的屬性對象，那麼如今咱們要經過屬性對象獲得相應的屬性值將其注入到咱們的Bean中，這些Bean也就是一些SpringBoot啓動後爲咱們自動配置生成的Bean，固然SpringBoot優先使用咱們配置的Bean這個功能是如何實現的,咱們往下看一下就明白了。

首先咱們須要一個功能Bean，能夠把這個Bean看作是SpringBoot框架啓動後在容器裏面生成的爲咱們服務的內置Bean,簡單的寫一個。

//@Component   這裏很重要，若是咱們添加了這個註解那麼，按照咱們下面的設置SpringBoot會優先使用咱們配置的這個Bean，這是符合SpringBoot框架優先使用自定義Bean的原則的。
public class HelloService {

    private String msg = "service";//若是自動配置沒有讀入成功，那麼爲默認值

    public String say() {
        return "hello " + msg;
    }//爲咱們服務的方法

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

如今編寫咱們的自動配置類。

@Configuration //配置類
@EnableConfigurationProperties(HelloProperties.class)//這裏就是前面說的，這個註解讀入咱們的配置對象類
@ConditionalOnClass(HelloService.class)//當類路徑存在這個類時纔會加載這個配置類，不然跳過,這個頗有用好比不一樣jar包間類依賴，依賴的類不存在直接跳過，不會報錯
public class HelloAutoConfiguration {

    @Autowired
    private HelloProperties helloProperties;

    @Bean
    @ConditionalOnMissingBean(HelloService.class)//這個配置就是SpringBoot能夠優先使用自定義Bean的核心所在，若是沒有咱們的自定義Bean那麼纔會自動配置一個新的Bean
    public HelloService auto(){
        HelloService helloService =new HelloService();
        helloService.setMsg(helloProperties.getMsg());
        return helloService;
    }

}

好了如今自動配置的類也寫好了，咱們能夠啓動一下SpringBoot應用，測試一下。

三,測試自動配置

@SpringBootApplication
@RestController
public class MyRun {

    @Autowired
    private HelloService helloService;

    @RequestMapping("/auto/home")
    public String home(){
        return helloService.say();
    }

    public static void main(String[] args) {
        SpringApplication.run(MyRun.class,args);
    }
}

ok ,運行後訪問你會看到：

hello world

表明咱們的自動配置功能成功。

四,SpringBoot管理自動配置

其實在不少時候咱們的配置是在不少jar包裏的，那麼咱們新的應用該怎麼讀入這些jar包裏的配置文件呢，SpringBoot是這樣管理的。

最主要的註解就是@enableAutoConfiguration,而這個註解會導入一個EnableAutoConfigurationImportSelector的類,而這個類會去讀取一個spring.factories下key爲EnableAutoConfiguration全限定名對應值.

 

# 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.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration,\
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.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.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.jms.hornetq.HornetQAutoConfiguration,\
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.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.velocity.VelocityAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
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

 

因此若是須要咱們能夠在咱們的resources目錄下建立spring.factories下添加相似的配置便可。。

 

ok，自動配置的原理差很少就這樣，我如今瞭解的並不深刻，還須要繼續學習。