元注解
元标签有 @Retention、@Documented、@Target、@Inherited、@Repeatable 5 种。
FactoryBean getObject
1. 静态注入
2. 动态引入
基于ImportSelector接口实现
3. 基于ImportBeanDefinition
4. spring.factories
@conditional 加载到容器的条件
第一个决定要加载的类型, 第二个决定是否加载?
扩展下. 其实springCloud组件 很多用到@Import @Conditional , 还有些select等, 顺藤摸瓜 我简答列列举几个:
- SpringBoot 启动注解
@SpringBootApplication-->@EnableAutoConfiguration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {}
@Import(AutoConfigurationImportSelector.class)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {}
重点说下Selector:
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {}
最顶层继承了ImportSelector 和 Aware接口:
- ImportSelector---控制哪些类可以被加载到Spring容器进行管理
public interface ImportSelector {
/**
* Select and return the names of which class(es) should be imported based on
* the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
*/
String[] selectImports(AnnotationMetadata importingClassMetadata);
}
protected List
List
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;
}
protected Class getSpringFactoriesLoaderFactoryClass() {
return EnableAutoConfiguration.class;
}
其实最终是寻找EnableAutoConfiguration对应的类组合, EnableAutoConfiguration来自package org.springframework.boot.autoconfigure;
所以最终初始化时, 是加载了spring-boot-autoconfigure里面的spring.factories的内容, 简单列举出现:
说明下:
SpringFactoriesLoader属于Spring框架私有的一种扩
展方案，其主要功能就是从指定的配置文件META-INF/spring.factories加载配置。
public final class SpringFactoriesLoader {
/**
* The location to look for factories.
* Can be present in multiple JAR files.
*/
public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class);
private static final Map> cache = new ConcurrentReferenceHashMap<>();
}