springboot的SPI机制

曾经终败给现在 2023-10-05 15:39 11阅读 0赞

SPI，即Service Provider Interface，为某个接口寻找服务实现的机制。

在springboot的启动类上面，我们一般会标注启动类注解@SpringBootApplication，而@SpringBootApplication是@SpringBootConfiguration @EnableAutoConfiguration @ComponentScan等多个注解的合体，SPI机制的入口注解是@EnableAutoConfiguration，即springboot标注该注解，表示可以实现自动配置.

@EnableAutoConfiguration注解如下

@Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import({EnableAutoConfigurationImportSelector.class})
    public @interface EnableAutoConfiguration {
        String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    
        Class<?>[] exclude() default {};
    
        String[] excludeName() default {};
    }

我们可以看到，该注解import了一个EnableAutoConfigurationImportSelector类

该类有一个方法

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
            List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());
            Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct.");
            return configurations;
        }

该方法会通过SpringFactoriesLoader**遍历整个ClassLoader中所有jar包下的spring.factories文件**。

所以我们自己开发的组件，如果想无缝融合到springboot中，就可以构建一个starter包，在该包中META-INF/spring.factories写入我们的组件的启动类的名称，springboot就可以通过SPI机制在启动的时候，自动加载并启动我们的组件。

SpringFactoriesLoader 源码解析可参考

[https://andyboke.blog.csdn.net/article/details/84025989?utm\_medium=distribute.pc\_relevant.none-task-blog-searchFromBaidu-2.control&depth\_1-utm\_source=distribute.pc\_relevant.none-task-blog-searchFromBaidu-2.control][https_andyboke.blog.csdn.net_article_details_84025989_utm_medium_distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control_depth_1-utm_source_distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control]

[https_andyboke.blog.csdn.net_article_details_84025989_utm_medium_distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control_depth_1-utm_source_distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control]: https://andyboke.blog.csdn.net/article/details/84025989?utm_medium=distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-searchFromBaidu-2.control