[Java知识库] 14、Spring-Boot 加载Bean的几种方式

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[Java知识库]14、Spring-Boot 加载Bean的几种方式

01、学习内容

1、Spring-Boot 加载Bean的几种方式

2、自定义starter，顺便理解springboot加载原理和机制

02、探索springboot的加载bean几种方式

springboot启动类上的注解是一个复合注解：

@SpringBootConfiguration
- 配置类 + @Bean
- 配置类作用：方便扩展、方便集成，不受包约束。
@EnableAutoConfiguration
- springboot内部的starter加载的原理
  - 内部其实：配置+@Bean
@ComponentScan （主要是用加载当前项目自身开发的bean）
- 扫包 + @Service、@Controller、@Component

三者的作用都是一致的：把相关的bean加载ioc容器中。

03、@Enablexxx开关类

01、分析

未来在程序中我们会大量的看到@Enablexxx开关注解。这个注解本身没有加载bean到ioc容器作用，只是起到一个标记作用，真正把相关配置类加载到ioc容器的机制是：@Import。

@Import 才是开关类中，指定的类，而这个指定类要么是：

配置类（被@Configuration标记的类）
实现ImportSelector接口的类。

02、格式

@Enablexxxx  +  @Import(配置类 || 实现ImportSelector接口的类。)

03、import机制的作用

如果你要去加载一个外部的配置类，你可以使用@Import机制。

springboot的starter的中一系列的配置类+@Bean是怎么加载进去：就是通过@Import机制

什么是外部的配置类？

当前默认包（启动类包）以外的配置类，都属于：外部配置类。

当前项目启动类包以外
自定义starter的配置类
springboot自身提供的starter配置类

04、@Import + @Configuration配置类

具体实现如下：

加载的bean

package com.selector.service;


public class UserService {
    public void sayHello(){
        System.out.println("say hello !!!");
    }
}

开关注解

package com.selector.anno;

import com.config.UserServiceConfiguration;
import com.selector.UserServiceImportSelector;
import org.springframework.context.annotation.Import;

import java.lang.annotation.*;


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
//以上注解都是默认存在的，可以参考@EnableAutoConfigration
@Import(UserServiceConfiguration.class)
public @interface EnableUserService2 {
}

配置类实现

package com.config;

import com.config.service.UserService;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;


@Configuration
public class UserServiceConfiguration {

    @Bean
    public UserService userService(){
        return new UserService();
    }
}

在需要的启动类上声明注解即可

package com.kuangstudy;

import com.config.UserServiceConfiguration;
import com.config.anno.EnableUserService;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@SpringBootApplication
//启动类上声明即可
@EnableUserService
public class SpringbootEnableImportApplication {

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

}

测试

package com.kuangstudy;

import com.config.service.UserService;
import com.selector.service.UserService2;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class SpringbootEnableImportApplicationTests {

    //因为已经在IOC容器内所以是可以被注入的
    @Autowired
    private UserService userService;


    @Test
    void contextLoads() {
        userService.sayHello();
    }

}

运行结果：say hello !!! 说明成功

05、@Import + importselector接口

无论你是用配置类还是importselector接口的方式，它们的目的都是一致的：

要么用配置类+@Bean，加载到ioc容器中
要么用ImportSelector接口的数组的方式指定加载到ioc容器中

具体实现如下：

加载的bean

package com.selector.service;


public class UserService2 {
    public void sayHello(){
        System.out.println("say hello !!!");
    }
}

开关注解

package com.selector.anno;

import com.config.UserServiceConfiguration;
import com.selector.UserServiceImportSelector;
import org.springframework.context.annotation.Import;

import java.lang.annotation.*;


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(UserServiceImportSelector.class)
public @interface EnableUserService2 {
}

importselector实现

package com.selector;

import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;

// 这里要实现ImportSelector类
public class UserServiceImportSelector implements ImportSelector {

    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        //这里是数组的形式，可以填写多个类
        return new String[]{"com.selector.service.UserService2"};
    }
}

在需要的启动类上声明注解即可

package com.kuangstudy;

import com.config.UserServiceConfiguration;
import com.config.anno.EnableUserService;
import com.selector.anno.EnableUserService2;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Import;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@SpringBootApplication
@EnableUserService2
public class SpringbootEnableImportApplication {

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

}

测试

package com.kuangstudy;

import com.config.service.UserService;
import com.selector.service.UserService2;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class SpringbootEnableImportApplicationTests {

    @Autowired
    private UserService2 userService2;


    @Test
    void contextLoads() {
        userService2.sayHello();
    }

}

运行结果：say hello !!! 说明成功

05、 importselector接口存在的意义是什么？

就专门去加载springboot提供的starter和自定义的starter的一种机制。

spring-boot-starter-web
- 配置类 + @Bean
mybatis-boot-starter
- 配置类 + @Bean
kaptcha-boot-starter
- 配置类 + @Bean

官方starter

因为springboot的autoconfiguration的目录META-INF提供专门的配置文件spring.factories。这个文件中就定义springboot中starter所需要加载的所有的配置类。

spring-boot-autoconfigure-2.6.1.jar 包下：

# 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.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\
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.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\
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.Neo4jReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\
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.ElasticsearchRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
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.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\
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.neo4j.Neo4jAutoConfiguration,\
org.springframework.boot.autoconfigure.netty.NettyAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\
org.springframework.boot.autoconfigure.r2dbc.R2dbcTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
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.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
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.sql.init.SqlInitializationAutoConfiguration,\
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.ReactiveMultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebSessionIdResolverAutoConfiguration,\
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

自定义starter

如果你要自定义starter，你就必须在你maven工程中的resources目录下新建一个META-INF/spring.factoires。把你项目中自己的配置类在这个文件中进行指定即可。

mybatis-plus-boot-starter-3.4.2.jar 如下：

# Auto Configure
org.springframework.boot.env.EnvironmentPostProcessor=\
  com.baomidou.mybatisplus.autoconfigure.SafetyEncryptProcessor
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.baomidou.mybatisplus.autoconfigure.MybatisPlusLanguageDriverAutoConfiguration,\
  com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration

如何加载这些上面的这些starter的配置类的呢？

原理是：importselector机制，处理者：AutoConfigurationImportSelector

第一步：这个接口的实现类 AutoConfigurationImportSelector 中，它会读取项目中所有的META-INF/spring.factoires这个文件
第二步：把这个文件中所有关于这个注解EnableAutoConfiguration的配置类全部找出来。
第三步：把找出来的配置类根据条件注解@Condition进行过滤，过滤放入到集合set
第四步：把set集合中的已经明确加载的配置类，放入到数组中。
第五步：结束