源码分析之SpringBoot自动装配原理

清疚 2022-11-13 06:29 231阅读 0赞

### 源码分析之SpringBoot自动装配原理 ###

*   *  1、自动装配流程
     *  2 、@SpringBootConfiguration
     *  3、@EnableAutoConfiguration
     *  4、往期佳文
     *   *  4.1、面试系列
         *  4.2、技术系列
         *  4.3、源码系列

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

## 1、自动装配流程 ##

@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 { 
    	~~~
    }

## 2 、@SpringBootConfiguration ##

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Configuration
    public @interface SpringBootConfiguration { 
    	~~~
    }

## 3、@EnableAutoConfiguration ##

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @AutoConfigurationPackage
    @Import(AutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration { 
    	~~~
    }

自动配置导入选择器

public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
    		ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { 
    	@Override
    	public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) { 
    		Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector,
    				() -> String.format("Only %s implementations are supported, got %s",
    						AutoConfigurationImportSelector.class.getSimpleName(),
    						deferredImportSelector.getClass().getName()));
    		// 获取自动装配实体
    		AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
    				.getAutoConfigurationEntry(annotationMetadata);
    		this.autoConfigurationEntries.add(autoConfigurationEntry);
    		for (String importClassName : autoConfigurationEntry.getConfigurations()) { 
    			this.entries.putIfAbsent(importClassName, annotationMetadata);
    		}
    	}
    	// 具体用来加载自动配置累的方法
    	protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) { 
    		if (!isEnabled(annotationMetadata)) { 
    			return EMPTY_ENTRY;
    		}
    		AnnotationAttributes attributes = getAttributes(annotationMetadata);
    		// 获取候选的配置类，即使后宫佳丽三千，也是要筛选的
    		List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
    		// 根据情况自动配置需要的配置类和不需要的配置类
    		configurations = removeDuplicates(configurations);
    		Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    		checkExcludedClasses(configurations, exclusions);
    		configurations.removeAll(exclusions);
    		configurations = getConfigurationClassFilter().filter(configurations);
    		fireAutoConfigurationImportEvents(configurations, exclusions);
    		// 返回最终需要的配置
    		return new AutoConfigurationEntry(configurations, exclusions);
    	}
    	// 去配置文件spring.factories加载enableAutoConfiguration 默认118个
    	protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { 
    		List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
    			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;
    	}
    	@Override
    	public Iterable<Entry> selectImports() { 
    		if (this.autoConfigurationEntries.isEmpty()) { 
    			return Collections.emptyList();
    		}
    		// 筛选配置类
    		Set<String> allExclusions = this.autoConfigurationEntries.stream()
    		        .map(AutoConfigurationEntry::getExclusions)
    		        .flatMap(Collection::stream)
    		        .collect(Collectors.toSet());
    		Set<String> processedConfigurations = this.autoConfigurationEntries.stream()
    				.map(AutoConfigurationEntry::getConfigurations).flatMap(Collection::stream)
    				.collect(Collectors.toCollection(LinkedHashSet::new));
    		processedConfigurations.removeAll(allExclusions);
    	
    		return sortAutoConfigurations(processedConfigurations, getAutoConfigurationMetadata()).stream()
    				.map((importClassName) -> new Entry(this.entries.get(importClassName), importClassName))
    				.collect(Collectors.toList());
    	}
    	
    }

自动配置实体属性

protected static class AutoConfigurationEntry { 
    	// 用来存储需要的配置项
    	private final List<String> configurations;
    	// 用来存储排除的配置项
    	private final Set<String> exclusions;
    	
    	private AutoConfigurationEntry() { 
    		this.configurations = Collections.emptyList();
    		this.exclusions = Collections.emptySet();
    	}
    }

## 4、往期佳文 ##

### 4.1、面试系列 ###

1、[吊打面试官之一面自我介绍][Link 1]  
2、[吊打面试官之一面项目介绍][Link 2]  
3、[吊打面试官之一面系统架构设计][Link 3]  
4、[吊打面试官之一面你负责哪一块][Link 4]

······持续更新中······

--------------------

### 4.2、技术系列 ###

1、[吊打面试官之分布式会话][Link 5]  
2、[吊打面试官之分布式锁][Link 6]  
3、[吊打面试官之乐观锁][Link 7]  
4、[吊打面试官之幂等性问题][Link 8]  
5、[吊打面试关之分布式事务][Link 9]

······持续更新中······

### 4.3、源码系列 ###

1、[源码分析之SpringBoot启动流程原理][SpringBoot]

······持续更新中······

--------------------

[Link 1]: https://blog.csdn.net/wtyicy/article/details/114933478
[Link 2]: https://blog.csdn.net/wtyicy/article/details/114983053
[Link 3]: https://blog.csdn.net/wtyicy/article/details/115005012
[Link 4]: https://blog.csdn.net/wtyicy/article/details/115064661
[Link 5]: https://blog.csdn.net/wtyicy/article/details/114685293
[Link 6]: https://blog.csdn.net/wtyicy/article/details/114915987
[Link 7]: https://blog.csdn.net/wtyicy/article/details/114915177
[Link 8]: https://blog.csdn.net/wtyicy/article/details/114888754
[Link 9]: https://blog.csdn.net/wtyicy/article/details/115081790
[SpringBoot]: https://blog.csdn.net/wtyicy/article/details/115181539