文章目录
- 一、Spring生命周期核心底层源码剖析---扫描
- [二、Spring生命周期核心底层源码剖析---bean的创建<font color="red">（持续更新中~~~）](#二、Spring生命周期核心底层源码剖析—bean的创建（持续更新中~~~）)
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：
java
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，不存在返回True，将对象需封装为BeanDefinitionHolder对象，注册到BeanDefinitionMap中，若存在，会判断是否为同样类型，若是，返回false，不重新注入，若存在且不是同样类型，抛出异常
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
//将BeanDefinition加入BeanDefinitionMap中
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）：
java
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;
}扫描完毕后，那接下来就是创建非懒加载的Bean，示例代码如下：
java
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
context.refresh();refresh方法的源代码中的
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
即为初始化非懒加载的单例bean，那就先来探索其实现的过程是如何的
java
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Register a default embedded value resolver if no BeanFactoryPostProcessor
// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}其方法preInstantiateSingletons即为初始化非懒加载的bean，继续点进方法（执行过程看参考注释信息）：
java
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
//1、获取其class名称形式为：com.xx.xx.Xxxx.class
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
//2、遍历获取的资源数据
for (String beanName : beanNames) {
//3、合并其BeanDefinition，存在父子关系的Bean，需要合并为一个BeanDefinition，底层会结合BeanDefinition中的parentName与是否为RootBeanDefinition，判断其是否需要多个BeanDefinition合并
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//4、判断当前的Bean是否为非懒加载的单例bean，并且当前的BeanDefinition为非抽象的
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//5、判断其bean是否为factoryBean
if (isFactoryBean(beanName)) {
//6、在beanName基础上加&符号，获取单例池中的对象
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
//7、判断其拿出来的对象是否为factoryBean
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
//8、如果是当前对象为factoryBean且实现了SmartFactoryBean接口，此时需要执行isEagerInit方法
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
//9、上一步执行的结果若为true，创建其getObject中的方法，并将其加入到缓存的Map中
if (isEagerInit) {
getBean(beanName);
}
}
}
//10、如果不是factoryBean，直接创建单例bean
else {
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
//创建所有的非懒加载的单例bean后，此处的逻辑为判断当前的单例对象是否实现了SmartInitializingSingleton接口，若实现了，这里需要调用其对象中的afterSingletonsInstantiated方法执行相关业务逻辑代码
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
.tag("beanName", beanName);
SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
smartInitialize.end();
}
}
}