1. BeanDefinition简介
前面讲的解析bean标签，本质就是将bean的信息封装成BeanDefinition对象的过程，最后放入容器beanDefinitionMap中。spring 要根据 BeanDefinition对象来实例化bean，只要把解析的标签，扫描的注解类封装成BeanDefinition对象，spring才能实例化bean。
BeanDefinition有三个实现类，ChildBeanDefinition、GenericBeanDefinition、RootBeanDefinition，三者都继承 AbstractBeanDefinition，对三个子类共同的类信息进行抽象。如果配置文件中定义了父
2. BeanDefinition的属性
上一篇文章中并未对BeanDefinition属性作详细分析，本文再次回到上文提到的BeanDefintionParserDelegate的方法parseBeanDefinitionAttributes方法。
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) {
// 解析scope标签
if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {
error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
}
else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) {
bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE));
}
else if (containingBean != null) {
// Take default from containing bean in case of an inner bean definition.
bd.setScope(containingBean.getScope());
}
// 解析abstract标签
if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {
bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));
}
// 解析lazy-init标签
String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
if (isDefaultValue(lazyInit)) {
lazyInit = this.defaults.getLazyInit();
}
bd.setLazyInit(TRUE_VALUE.equals(lazyInit));
// 解析 autowire 标签
String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);
bd.setAutowireMode(getAutowireMode(autowire));
// 解析 depends-on 标签
if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {
String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);
bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));
}
// 解析 autowire-candidate 标签
String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);
if (isDefaultValue(autowireCandidate)) {
String candidatePattern = this.defaults.getAutowireCandidates();
if (candidatePattern != null) {
String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern);
bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
}
}
else {
bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate));
}
// 解析 primary 标签
if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {
bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));
}
// 解析 init-method 标签
if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {
String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);
bd.setInitMethodName(initMethodName);
}
else if (this.defaults.getInitMethod() != null) {
bd.setInitMethodName(this.defaults.getInitMethod());
bd.setEnforceInitMethod(false);
}
// 解析 destroy-method 标签
if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {
String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);
bd.setDestroyMethodName(destroyMethodName);
}
else if (this.defaults.getDestroyMethod() != null) {
bd.setDestroyMethodName(this.defaults.getDestroyMethod());
bd.setEnforceDestroyMethod(false);
}
// 解析 factory-method 标签
if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {
bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));
}
// 解析 factory-bean 标签
if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {
bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));
}
return bd;
}
由于BeanDefinition的实现类都继承自父类AbstractBeanDefinition，父类中有三个引用的属性ConstructorArgumentValues、MutablePropertyValues、MethodOverrides，所以GenericBeanDefinition最终包含的属性如下图：
id：Bean 的唯一标识名。它必须是合法的 XMLID，在整个 XML 文档中唯一；name：用来为 id 创建一个或多个别名。它可以是任意的字母符合。多个别名之间用逗号或空格分开；class：用来定义类的全限定名（包名＋类名）。只有子类 Bean 不用定义该属性；parent：子类 Bean 定义它所引用它的父类 Bean，这时前面的 class 属性失效，子类 Bean 会继承父类 Bean 的所有属性，子类 Bean 也可以覆盖父类 Bean 的属性，注意：子类 Bean 和父类 Bean 是同一个 Java 类；abstract（默认为"false"）：用来定义 Bean 是否为抽象 Bean。它表示这个 Bean 将不会被实例化，一般用于父类 Bean，因为父类 Bean 主要是供子类 Bean 继承使用；lazy-init（默认为"false"）：用来定义这个 Bean 是否实现懒初始化。如果为"false"，它将在 BeanFactory 启动时初始化所有的 SingletonBean。反之，如果为"true",它只在 Bean 请求时才开始创建 SingletonBean；autowire（自动装配，默认为"default"）：它定义了 Bean 的自动装载方式；
--"no"：不使用自动装配功能；
--"byName"：通过 Bean 的属性名实现自动装配;
--"byType"：通过 Bean 的类型实现自动装配;
--"constructor"：类似于 byType，但它是用于构造函数的参数的自动组装;
--"autodetect"：通过 Bean 类的反省机制（introspection）决定是使用"constructor"还是使用"byType"。depends-on（依赖对象）：这个 Bean 在初始化时依赖的对象，这个对象会在这个 Bean 初始化之前创建；init-method：用来定义 Bean 的初始化方法，它会在 Bean 组装之后调用。它必须是一个无参数的方法；destroy-method：用来定义 Bean 的销毁方法，它在 BeanFactory 关闭时调用。同样，它也必
须是一个无参数的方法。它只能应用于 singletonBean。factory-method：定义创建该 Bean 对象的工厂方法。它用于下面的"factory-bean"，表示这个 Bean 是通过工厂方法创建，此时，"class"属性失效。factory-bean:定义创建该 Bean 对象的工厂类。如果使用了"factory-bean"则"class"属性失效。autowire-candidate：采用 xml 格式配置 bean 时，将MutablePropertyValues：用于封装ConstructorArgumentValues：用于封装MethodOverrides：用于封装 lookup-method 和 replaced-method 标签的信息，同样的类里面有一个 Set 对象添加 LookupOverride 对象和ReplaceOverride 对象。
3. component-scan标签解析过程
3.1 流程概览
3.2 详细过程
前面一文提到，自定义标签解析BeanDefinitionParserDelegate类，执行parseCustomElement方法；
public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
// 获取namespaceURI
String namespaceUri = getNamespaceURI(ele);
if (namespaceUri == null) {
return null;
}
// 解析namespaceURI对应的handler类
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
// 执行handler的解析方法
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
上述过程主要完成以下步骤：step1: 获取namespaceURI；step2: 解析namespaceURI对应的handler类；step3：执行handler方法解析。
step1与step2前文已分析，以component-scan为例，分析step3，代码进入ComponentScanBeanDefinitionParser的parse方法
public BeanDefinition parse(Element element, ParserContext parserContext) {
/**
* 1. 包扫描.class后缀的文件
* 2. 判断类上是否有注解
* 3. GenericBeanDefinition genericBeanDefinition = new GenericBeanDefinition();
* genericBeanDefinition.setBeanClass(BeanClass.class);
* 4. 完成beanDefinition的注册
*/
String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
// Actually scan for bean definitions and register them.
// 创建扫描器
ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
// 扫描器扫描
Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
// 注册bean包含的组件
registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
return null;
}
上述过程总共分为三步：step1：configureScanner方法创建扫描器；step2：doScan方法扫描器扫描；step3：registerComponents注册bean包含的组件。
进入上述step2，进入ClassPathBeanDefinitionScanner的doScan方法,
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) {
// 扫描有注解的类并封装成beanDefinition对象
Set<BeanDefinition> 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) {
// 支持@Lazy @Primary @DependOn注解
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;
}
上述doScan方法主要做了以下三步：step1: findCandidateComponents扫描有注解的类并封装成beanDefinition对象；step2: processCommonDefinitionAnnotations方法支持@Lazy @Primary @DependOn注解；step3：注册BeanDefinition。
继续进入上述step1中的findCandidateComponents方法，来到ClassPathScanningCandidateComponentProvider类的scanCandidateComponents方法，完成以下步骤：step1: getResources递归获取.class后缀的文件；step2: getMetadataReader方法，获取元数据AnnotationMetadataReadingVisitor对象，该元数据收集了扫描类的任何信息；step3：判断includeFilters是否跟元数据中的注解匹配，如果匹配就实例化该类，创建BeanDefinition对象。
前面还有一个步骤step3：registerComponents注册bean包含的组件还未分析，进入该方法
protected void registerComponents(
XmlReaderContext readerContext, Set<BeanDefinitionHolder> beanDefinitions, Element element) {
Object source = readerContext.extractSource(element);
CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), source);
for (BeanDefinitionHolder beanDefHolder : beanDefinitions) {
compositeDef.addNestedComponent(new BeanComponentDefinition(beanDefHolder));
}
boolean annotationConfig = true;
if (element.hasAttribute(ANNOTATION_CONFIG_ATTRIBUTE)) {
annotationConfig = Boolean.parseBoolean(element.getAttribute(ANNOTATION_CONFIG_ATTRIBUTE));
}
if (annotationConfig) {
// 如果类中的属性有注解，注册注解配置处理器
Set<BeanDefinitionHolder> processorDefinitions =
AnnotationConfigUtils.registerAnnotationConfigProcessors(readerContext.getRegistry(), source);
for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
compositeDef.addNestedComponent(new BeanComponentDefinition(processorDefinition));
}
}
readerContext.fireComponentRegistered(compositeDef);
}
随后进入AnnotationConfigUtils.registerAnnotationConfigProcessors，
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
// @Configuration注解的处理器ConfigurationClassPostProcessor
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// @Autowired注解的处理器AutowiredAnnotationBeanPostProcessor
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// CommonAnnotationBeanPostProcessor处理器.
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
return beanDefs;
}
上面提到了三类处理器ConfigurationClassPostProcessor，AutowiredAnnotationBeanPostProcessor，CommonAnnotationBeanPostProcessor，分别对不同注解作处理，最后封装到BeanDefinition中，注册到容器。
进入ConfigurationClassPostProcessor的processConfigBeanDefinitions方法，如下:
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
......
// 解析所有加了@Configuration注解的类
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
do {
// 解析@Component @ComponentScan @ComponentScans @Bean @Import @ImportResource
parser.parse(candidates);
parser.validate();
......
}
上述方法主要解析加了@Configuration的类，以及@Component @ComponentScan @ComponentScans @Bean @Import @ImportResource注解，后者是通过parse方法完成的，进入parse方法一路走下来回到processConfigurationClass方法，如下图
protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) throws IOException {
......
do {
sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
}
while (sourceClass != null);
......
}
随后进入doProcessConfigurationClass方法，完成@Component @ComponentScan @ComponentScans @Bean @Import @ImportResource注解解析。
protected final SourceClass doProcessConfigurationClass(
ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
throws IOException {
// 解析 @Component
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass, filter);
}
// 解析 @PropertySource
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
// 解析 @ComponentScan @ComponentScans
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
Set<BeanDefinitionHolder> 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) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// 解析 @Import
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
// 解析 @ImportResource
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
// 解析 @Bean 方法
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// Process superclass, if any
if (sourceClass.getMetadata().hasSuperClass()) {
String superclass = sourceClass.getMetadata().getSuperClassName();
if (superclass != null && !superclass.startsWith("java") &&
!this.knownSuperclasses.containsKey(superclass)) {
this.knownSuperclasses.put(superclass, configClass);
// Superclass found, return its annotation metadata and recurse
return sourceClass.getSuperClass();
}
}
// No superclass -> processing is complete
return null;
}
同样跟踪AutowiredAnnotationBeanPostProcessor类，可以看到该类完成@Autowired @Value的解析，如下图：
public AutowiredAnnotationBeanPostProcessor() {
this.autowiredAnnotationTypes.add(Autowired.class);
this.autowiredAnnotationTypes.add(Value.class);
try {
this.autowiredAnnotationTypes.add((Class<? extends Annotation>)
ClassUtils.forName("javax.inject.Inject", AutowiredAnnotationBeanPostProcessor.class.getClassLoader()));
logger.trace("JSR-330 'javax.inject.Inject' annotation found and supported for autowiring");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}
类似跟踪CommonAnnotationBeanPostProcessor类，可以看到该类完成@Resource @PostConstruct @PreDestroy的解析，如下图：
static {
webServiceRefClass = loadAnnotationType("javax.xml.ws.WebServiceRef");
ejbClass = loadAnnotationType("javax.ejb.EJB");
resourceAnnotationTypes.add(Resource.class);
if (webServiceRefClass != null) {
resourceAnnotationTypes.add(webServiceRefClass);
}
if (ejbClass != null) {
resourceAnnotationTypes.add(ejbClass);
}
}
......
public CommonAnnotationBeanPostProcessor() {
setOrder(Ordered.LOWEST_PRECEDENCE - 3);
setInitAnnotationType(PostConstruct.class);
setDestroyAnnotationType(PreDestroy.class);
ignoreResourceType("javax.xml.ws.WebServiceContext");
}
4. 示例
创建一个BeanDefinitionTest类，实现BeanDefinitionRegistryPostProcessor接口，并在方法中完成设置Bean的类型为BeanClass，然后设置BeanClass对象的username属性与值，最后注册到容器中，代码如下
@Component
public class BeanDefinitionTest implements BeanDefinitionRegistryPostProcessor {
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
GenericBeanDefinition genericBeanDefinition = new GenericBeanDefinition();
genericBeanDefinition.setBeanClass(BeanClass.class);
MutablePropertyValues propertyValues = genericBeanDefinition.getPropertyValues();
propertyValues.addPropertyValue("username","wzj");
registry.registerBeanDefinition("beanClass",genericBeanDefinition);
}
BeanClass类如下：
@Data
public class BeanClass {
private String username;
}
测试类如下：
public class TestSpring {
@Autowired
private ApplicationContext applicationContext;
@Test
public void testComponentScan() {
applicationContext = new AnnotationConfigApplicationContext("com.wzj");
BeanClass beanClass = (BeanClass)applicationContext.getBean("beanClass");
BeanDefinitionTest beanDefinitionTest = (BeanDefinitionTest)applicationContext.getBean("beanDefinitionTest");
System.out.println("BeanClass-->" + beanClass.getUsername());
System.out.println("BeanDefinitionTest-->" + beanDefinitionTest.getClass());
}
代码目录结构如下与运行结果如下
5. 总结
本文以conmponent-scan标签为例，分析了主要流程，并结合源码讲述了BeanDefinition属性的解析、封装、以及最后注册到容器中，最后以一个思维导图总结每个流程中的大致步骤
另外，静态看源码可关注主流程，并做注释，动态debug示例进入源码可直观感受运行期间的值，源码分析不易，搞清楚主流程与思想比源码本身更重要。