【Spring生命周期核心底层源码之剖析】

一、Spring生命周期核心底层源码剖析—扫描

1.1、Spring底层扫描机制doScan方法源码剖析

其源代码如下：

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
		for (String basePackage : basePackages) {
			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
			//遍历其获取到的BeanDefinition对象
			for (BeanDefinition candidate : candidates) {
				//为其BeanDefinition对象进行属性赋值，例如scope，beanName等
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				if (candidate instanceof AbstractBeanDefinition) {
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}
				if (candidate instanceof AnnotatedBeanDefinition) {
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
				//判断当前的bean是否已经在Spring容器中存在，存在需封装为BeanDefinitionHolder对象
				if (checkCandidate(beanName, candidate)) {
					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
					definitionHolder =
							AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
					beanDefinitions.add(definitionHolder);
					registerBeanDefinition(definitionHolder, this.registry);
				}
			}
		}
		return beanDefinitions;
	}

1、其主要是通过传入的包路径进行资源加载，加载时方法为上诉代码的for循环下的第一行代码的findCandidateComponents()方法，可以详细看此方法，是如何加载资源的，其方法代码如下（具体说明以及解析过程可参考注释）：

public Set<BeanDefinition> findCandidateComponents(String basePackage) {
		//此处主要是判断项目是否配置了相关的bean文件，若有，就不需要再逐个类进行扫描+判断是否为Bean
		if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
			return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
		}
		//大部分的业务都会走如下方法
		else {
			return scanCandidateComponents(basePackage);
		}
	}
	
//scanCandidateComponents方法具体实现为
private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
		Set<BeanDefinition> candidates = new LinkedHashSet<>();
		try {
			//1、资源路径组装解析
			String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
					resolveBasePackage(basePackage) + '/' + this.resourcePattern;
			//2、利用类元数据读取器读取器路径下包含的资源数据
			Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
			boolean traceEnabled = logger.isTraceEnabled();
			boolean debugEnabled = logger.isDebugEnabled();
			//3、遍历类元数据读取器获取到的资源数据（class资源文件数据）
			for (Resource resource : resources) {
				if (traceEnabled) {
					logger.trace("Scanning " + resource);
				}
				try {
					//4、获取当前类元数据(calss)具体资源信息
					MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
					//5、判断当前的类（class）上包含的是否包含排除注解excludeFilters以及非排除注解includeFilters，以及是否包含相关的条件注解Conditional
					if (isCandidateComponent(metadataReader)) {
						//6、创建一个BeanDefinition对象，用于封装其类特征信息，例如：beanClass、scope、lazyInit等属性
						ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
						//7、将类资源数据加入到BeanDefinition中
						sbd.setSource(resource);
						//8、判断当前的类资源是否是独立的（例如是否是内部类等），除此歪，需要判断其是否为接口或者抽象类，如果是抽象类，那类中必须有被Lookup注解的方法，否则不会被当做bean
						if (isCandidateComponent(sbd)) {
							if (debugEnabled) {
								logger.debug("Identified candidate component class: " + resource);
							}
							//9、将封装好的BeanDefinition对象加入到返回的集合Set中
							candidates.add(sbd);
						}
						else {
							if (debugEnabled) {
								logger.debug("Ignored because not a concrete top-level class: " + resource);
							}
						}
					}
					else {
						if (traceEnabled) {
							logger.trace("Ignored because not matching any filter: " + resource);
						}
					}
				}
				catch (FileNotFoundException ex) {
					if (traceEnabled) {
						logger.trace("Ignored non-readable " + resource + ": " + ex.getMessage());
					}
				}
				catch (Throwable ex) {
					throw new BeanDefinitionStoreException(
							"Failed to read candidate component class: " + resource, ex);
				}
			}
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
		}
		return candidates;
	}