前言
前面講述了context的創(chuàng)建，接下來將進入到核心的bean的創(chuàng)建過程，前期的準(zhǔn)備工作已經(jīng)完成，相信很多人跟我一樣，看過了一遍只能有個大概的印象，接下來有時間的話我會考慮結(jié)合UML和腦圖這樣的出來和大家一起分享，有經(jīng)驗或者想一起學(xué)習(xí)的，希望可以聯(lián)系我，qq:616516146,言歸正傳，回到代碼。
1、prepareContext()
接下來回到最初代碼SpringApplication中run方法，我們先看prepareContext()這個方法。該方法是做context的準(zhǔn)備工作。我們進入代碼中看下他的具體實現(xiàn)。
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
/**
* 該方法對context進行了預(yù)設(shè)置，設(shè)置了ResourceLoader和ClassLoader，
* 并向bean工廠中添加了一個beanNameGenerator
*/
postProcessApplicationContext(context);
/**
*
* applyInitializers(context)方法
* 獲取到了我們或spring通過SpringApplication.setInitializers(xxx)
* 設(shè)置的應(yīng)用上下文初始化器集合
*/
applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
// Load the sources
Set<Object> sources = getSources();
Assert.notEmpty(sources, "Sources must not be empty");
/**
* 將各種bean裝載進context對象中
*/
load(context, sources.toArray(new Object[sources.size()]));
listeners.contextLoaded(context);
}
我們主要只討論 postProcessApplicationContext(context)、 applyInitializers(context)以及 load(context, sources.toArray(new Object[sources.size()]))這三個方法
- 1、postProcessApplicationContext(context)
該方法對context進行了預(yù)設(shè)置，設(shè)置了ResourceLoader和ClassLoader， 并向bean工廠中添加了一個beanNameGenerator - 2、applyInitializers(context)
該方法獲取到了我們或spring通過SpringApplication.setInitializers(xxx)設(shè)置的應(yīng)用上下文初始化器集合。 - 3、load(context, sources.toArray(new Object[sources.size()]))
這個方法主要是加載各種beans到context對象中的。sources代表各種資源對象，然后BeanDefinitionLoader的內(nèi)部通過各種xxxReader和xxxScanner讀取、解析這些資源對象中的beans
/**
* Load beans into the application context.
* @param context the context to load beans into
* @param sources the sources to load
* 這個方法主要是加載各種beans到context對象中的。
* sources代表各種資源對象，然后BeanDefinitionLoader
* 的內(nèi)部通過各種xxxReader和xxxScanner讀取、解析這些資源對象中的beans。
* 具體細節(jié)在 BeanDefinitionLoader中實現(xiàn)
*/
protected void load(ApplicationContext context, Object[] sources) {
logger.debug("開始執(zhí)行l(wèi)oad方法");
System.out.println("-------------開始執(zhí)行l(wèi)oad方法");
if (logger.isDebugEnabled()) {
logger.debug(
"Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
}
BeanDefinitionLoader loader = createBeanDefinitionLoader(
getBeanDefinitionRegistry(context), sources);
if (this.beanNameGenerator != null) {
loader.setBeanNameGenerator(this.beanNameGenerator);
}
if (this.resourceLoader != null) {
loader.setResourceLoader(this.resourceLoader);
}
if (this.environment != null) {
loader.setEnvironment(this.environment);
}
loader.load();
}
以上是load方法加載。
上面三個方法完成之后，prepareContext（）函數(shù)已經(jīng)準(zhǔn)備好了refresh上下文的基礎(chǔ)準(zhǔn)備工作。，接下來看refresh的相關(guān)工作。
2、refresh
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
/**
* 又注冊了關(guān)閉context時的鉤子
*/
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
這里我們進入refresh看看里面的具體實現(xiàn)，此處的refrsh調(diào)用的是AbstractApplicationContext的refrsh方法，之后又調(diào)用了context.registerShutdownHook();關(guān)閉了鉤子。進入到AbstractApplicationContext，看下refrsh的具體實現(xiàn),這里只截取了一部分代碼
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//BeanFactory創(chuàng)建
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke（調(diào)用） factory processors registered as beans in the context.
//DefaultListableBeanFactory,完成basepackage的掃描
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//DefaultListableBeanFactory
//該方法進行了非懶加載beans的初始化工作
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
這里我們只重點關(guān)注 finishBeanFactoryInitialization(beanFactory)這個方法。
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 bean post-processor
// (such as a PropertyPlaceholderConfigurer 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) {
logger.info("----------weaverAwareName:"+weaverAwareName);
//創(chuàng)建bean的實例
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.
//此處beanFactory是DefaultListableBeanFactory,獲取bean
beanFactory.preInstantiateSingletons();
}
最后調(diào)用了beanFactory的preInstantiateSingletons方法，此處的beanFactory是DefaultListableBeanFactory。那么我們就看下這個的重點。
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
this.logger.info("-----beanName:"+beanName);
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) () ->
((SmartFactoryBean<?>) factory).isEagerInit(),
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
/**
* 核心代碼
*/
getBean(beanName);
}
}
}
在這里看到了熟悉的getBean()方法，別的有興趣和時間再研究吧，先忽略別的，仔細研究getBean()方法，經(jīng)過追蹤發(fā)現(xiàn)，他調(diào)用了AbstractoryFactory的doGetBean()方法，這里是一大段的代碼。這里面有太多的代碼，我們先簡單描述，下節(jié)繼續(xù)深入。
//實例化依賴的bean之后可以實例化mbd本身了
//單例模式的創(chuàng)建
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> {
try {
/**
*核心創(chuàng)建bean
*/
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
這里是單例bean的實現(xiàn)，Spring默認(rèn)的bean都是單例的，在此我們看到了createBean()方法，spring源碼寫的確實是比較優(yōu)秀，根據(jù)方法名就能大致的知道其作用。這里的createBean()方法使用的是其子類的方法，這里摘取一點代碼片段看下
/**
* 鎖定class，根據(jù)設(shè)置的class屬性或者根據(jù)classname來解析class
*/
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
到此bean加載和創(chuàng)建的基本流程也就結(jié)束了，下一篇我們著重會分析一些具體的細節(jié)。
代碼的構(gòu)建請參考 github
該地址有相應(yīng)代碼的注釋
