Spring Boot 加载Bean的几种方式
01、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
- springboot内部的starter加载的原理
- @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。
02、@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;
/**
* @author 飞哥
* @Title: 学相伴出品
* @Description: 飞哥B站地址：https://space.bilibili.com/490711252
* 记得关注和三连哦！
* @Description: 我们有一个学习网站：https://www.kuangstudy.com
* @date 2021/12/26 20:23
*/
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.*;
/**
* @author 飞哥
* @Title: 学相伴出品
* @Description: 我们有一个学习网站：https://www.kuangstudy.com
* @date 2021/12/26 20:32
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(UserServiceImportSelector.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;
/**
* @author 飞哥
* @Title: 学相伴出品
* @Description: 飞哥B站地址：https://space.bilibili.com/490711252
* 记得关注和三连哦！
* @Description: 我们有一个学习网站：https://www.kuangstudy.com
* @date 2021/12/26 20:24
*/
@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
@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 {
@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;
public class UserServiceImportSelector implements ImportSelector {
@Override
public String[] selectImports(AnnotationMetadata importingClassMetadata) {
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
03、 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 Configureorg.springframework.boot.env.EnvironmentPostProcessor=\ com.baomidou.mybatisplus.autoconfigure.SafetyEncryptProcessororg.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
参考
- Spring boot Bean加载源码分析 http://blog.csdn.net/liaokailin/article/details/49107209
- Spring boot 自动配置原理分析
http://blog.csdn.net/liaokailin/article/details/49559951 - Spring Boot 使用Java代码创建Bean并注册到Spring中
http://blog.csdn.net/catoop/article/details/50558333