springboot如何实现自动装配bean源码赏析

待我称王封你为后i 2022-12-26 09:17 183阅读 0赞

## Spring Boot 自动装配 ##

最重要的注解@SpringBootApplication

@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 { 
    
    	@AliasFor(annotation = EnableAutoConfiguration.class)
    	Class<?>[] exclude() default { };
    
    	@AliasFor(annotation = EnableAutoConfiguration.class)
    	String[] excludeName() default { };
    
    	@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
    	String[] scanBasePackages() default { };
    
    	@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
    	Class<?>[] scanBasePackageClasses() default { };
    
    	@AliasFor(annotation = Configuration.class)
    	boolean proxyBeanMethods() default true;
    
    }

## EnableAutoConfiguration ##

是实现自动装配的核心注解

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

## getAutoConfigurationMetadata() ##

@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()));
    	AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
    			.getAutoConfigurationEntry(
    					// 加载配置元数据
    					getAutoConfigurationMetadata(), annotationMetadata);
    	this.autoConfigurationEntries.add(autoConfigurationEntry);
    	for (String importClassName : autoConfigurationEntry.getConfigurations()) {
    		this.entries.putIfAbsent(importClassName, annotationMetadata);
    	}
    }
    
    
    private AutoConfigurationMetadata getAutoConfigurationMetadata() {
    	if (this.autoConfigurationMetadata == null) {
    		// 加载配置信息
    		this.autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
    	}
    	return this.autoConfigurationMetadata;
    }
    static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader, String path) {
    	try {
    
    	    // 获取资源路径
    		Enumeration<URL> urls = (classLoader != null) ? classLoader.getResources(path)
    				: ClassLoader.getSystemResources(path);
    		Properties properties = new Properties();
    		while (urls.hasMoreElements()) {
    			properties.putAll(PropertiesLoaderUtils.loadProperties(new UrlResource(urls.nextElement())));
    		}
    		return loadMetadata(properties);
    	}
    	catch (IOException ex) {
    		throw new IllegalArgumentException("Unable to load @ConditionalOnClass location [" + path + "]", ex);
    	}
    }
    
    protected static final String PATH = "META-INF/spring-autoconfigure-metadata.properties";

注意： 这个文件在target编译后的文件夹中  
自动装配

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring.factories

该文件内存有:

# 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,\

## EnableConfigurationProperties ##

@ConfigurationProperties(prefix = "spring.redis")
    public class RedisProperties { 
    
    	/** * Database index used by the connection factory. */
    	private int database = 0;
    
    	/** * Connection URL. Overrides host, port, and password. User is ignored. Example: * redis://user:password@example.com:6379 */
    	private String url;
    
    	/** * Redis server host. */
    	private String host = "localhost";
    
    	/** * Login password of the redis server. */
    	private String password;
    
    	/** * Redis server port. */
    	private int port = 6379;
    
    	/** * Whether to enable SSL support. */
    	private boolean ssl;
    
    	/** * Connection timeout. */
    	private Duration timeout;
    
    	/** * Client name to be set on connections with CLIENT SETNAME. */
    	private String clientName;
    
    	
    
    }

希望通过本篇对于springboot自动装配的解读，让大家对springboot底层有了一个大致了解，只分析了主要方法，希望对大家有帮助  
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