Spring Boot 基于注解驱动源码分析--自动扫描-白红宇

上一篇文章介绍了spring的自动配置，那么spring是如何扫描包下所有类信息？本篇学习一下关于@ComponentScan、@ComponentScans注解解析和ClassPathBeanDefinitionScanner、PathMatchingResourcePatternResolver类的源码分析。

ClassPathBeanDefinitionScanner

A bean definition scanner that detects bean candidates on the classpath,  registering corresponding bean definitions with a given registry ({@code BeanFactory}  or {@code ApplicationContext}).复制代码

一个bean定义扫描器用来检测类路径下候选bean，提供一个注册器（registry）注册相应的bean定义

PathMatchingResourcePatternResolver

A {@link ResourcePatternResolver} implementation that is able to resolve a specified resource location path into one or more matching Resources.The source path may be a simple path which has a one-to-one mapping to a target {@link org.springframework.core.io.Resource}, or alternativelymay contain the special "{@code classpath*:}" prefix and/orinternal Ant-style regular expressions (matched using Spring's{@link org.springframework.util.AntPathMatcher} utility).Both of the latter are effectively wildcards.复制代码

一个ResourcePatternResolver的实现，可以为一个或者更多的资源解析指定的资源匹配位置路径；源路径可能是一个简单的路径一对一的映射目标或者另外可能含有特殊的前缀和基于ant正则表达式

大致了解两个关键类后，从注解解析入口开始进行源码分析

@ComponentScan 注解解析

在上一篇文章中了解到注解解析是在ConfigurationClassParser的doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)方法中进行

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)			throws IOException {		......				// 处理 @ComponentScan 注解				//获取资源类的ComponentScan、ComponentScans注解信息		Set
    
      componentScans = AnnotationConfigUtils.attributesForRepeatable(				sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);		if (!componentScans.isEmpty() &&				!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {			for (AnnotationAttributes componentScan : componentScans) {				// 配置类上有@ComponentScan注解，立即执行扫描				Set
     
       scannedBeanDefinitions =						this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());				// Check the set of scanned definitions for any further config classes and parse recursively if needed				for (BeanDefinitionHolder holder : scannedBeanDefinitions) {					if (ConfigurationClassUtils.checkConfigurationClassCandidate(							holder.getBeanDefinition(), this.metadataReaderFactory)) {						parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName());					}				}			}		}		......				return null;	}复制代码

这里的this.componentScanParser 是 ComponentScanAnnotationParser

public Set
    
      parse(AnnotationAttributes componentScan, final String declaringClass) {		Assert.state(this.environment != null, "Environment must not be null");		Assert.state(this.resourceLoader != null, "ResourceLoader must not be null");        //类路径Bean定义扫描器		ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,				componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);        ...... 省略读取注解信息，为ClassPathBeanDefinitionScanner初始化赋值                //扫描器扫描		return scanner.doScan(StringUtils.toStringArray(basePackages));复制代码

ClassPathBeanDefinitionScanner扫描

指定包进行扫描

protected Set
    
      doScan(String... basePackages) {		Assert.notEmpty(basePackages, "At least one base package must be specified");		Set
     
       beanDefinitions = new LinkedHashSet
      
       ();		for (String basePackage : basePackages) {		      //通过包路径寻找候选组件			Set
       
         candidates = findCandidateComponents(basePackage);			for (BeanDefinition candidate : candidates) {				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);				}				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;	}复制代码

通过包路径寻找候选组件

扫描classpath下的候选组件

public Set
    
      findCandidateComponents(String basePackage) {		Set
     
       candidates = new LinkedHashSet
      
       ();		try {			String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +					resolveBasePackage(basePackage) + '/' + this.resourcePattern;					//通过资源解析器获取resources			Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);			boolean traceEnabled = logger.isTraceEnabled();			boolean debugEnabled = logger.isDebugEnabled();			for (Resource resource : resources) {				if (traceEnabled) {					logger.trace("Scanning " + resource);				}				if (resource.isReadable()) {					try {						MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);						if (isCandidateComponent(metadataReader)) {							ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);							sbd.setResource(resource);							sbd.setSource(resource);							if (isCandidateComponent(sbd)) {								if (debugEnabled) {									logger.debug("Identified candidate component class: " + resource);								}								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 (Throwable ex) {						throw new BeanDefinitionStoreException(								"Failed to read candidate component class: " + resource, ex);					}				}				else {					if (traceEnabled) {						logger.trace("Ignored because not readable: " + resource);					}				}			}		}		catch (IOException ex) {			throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);		}		return candidates;复制代码

这里的this.resourcePatternResolver是通过PathMatchingResourcePatternResolver获取resources；通过MetaDataReader实例化ScannedGenericBeanDefinition。

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