spring4.1.8初始化原始碼學習三部曲之三:AbstractApplicationContext.refresh方法
本章是《spring4.1.8初始化原始碼學習三部曲》系列的終篇,重點是學習AbstractApplicationContext類的refresh()方法;
我們先回顧ClassPathXmlApplicationContext類的初始化過程如下程式碼:
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
refresh方法簡介
本章來學習refresh方法,具體的原始碼在AbstractApplicationContext類中,該方法的簡介請看下面原始碼中的註釋:
@Override
public void refresh() throws BeansException, IllegalStateException {
//startupShutdownMonitor物件在spring環境重新整理和銷燬的時候都會用到,確保重新整理和銷燬不會同時執行
synchronized (this.startupShutdownMonitor) {
// 準備工作,例如記錄事件,設定標誌,檢查環境變數等,並有留給子類擴充套件的位置,用來將屬性加入到applicationContext中
prepareRefresh();
// 建立beanFactory,這個物件作為applicationContext的成員變數,可以被applicationContext拿來用,
// 並且解析資源(例如xml檔案),取得bean的定義,放在beanFactory中
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 對beanFactory做一些設定,例如類載入器、spel解析器、指定bean的某些型別的成員變數對應某些物件等
prepareBeanFactory(beanFactory);
try {
// 子類擴充套件用,可以設定bean的後置處理器(bean在例項化之後這些後置處理器會執行)
postProcessBeanFactory(beanFactory);
// 執行beanFactory後置處理器(有別於bean後置處理器處理bean例項,beanFactory後置處理器處理bean定義)
invokeBeanFactoryPostProcessors(beanFactory);
// 將所有的bean的後置處理器排好序,但不會馬上用,bean例項化之後會用到
registerBeanPostProcessors(beanFactory);
// 初始化國際化服務
initMessageSource();
// 建立事件廣播器
initApplicationEventMulticaster();
// 空方法,留給子類自己實現的,在例項化bean之前做一些ApplicationContext相關的操作
onRefresh();
// 註冊一部分特殊的事件監聽器,剩下的只是準備好名字,留待bean例項化完成後再註冊
registerListeners();
// 單例模式的bean的例項化、成員變數注入、初始化等工作都在此完成
finishBeanFactoryInitialization(beanFactory);
// applicationContext重新整理完成後的處理,例如生命週期監聽器的回撥,廣播通知等
finishRefresh();
}
catch (BeansException ex) {
logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);
// 重新整理失敗後的處理,主要是將一些儲存環境資訊的集合做清理
destroyBeans();
// applicationContext是否已經啟用的標誌,設定為false
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}
接下來逐個分析吧:
prepareRefresh方法
prepareRefresh方法的原始碼如下:
protected void prepareRefresh() {
//記錄初始化開始時間
this.startupDate = System.currentTimeMillis();
//context是否關閉的標誌,設定為false
this.closed.set(false);
//context是否啟用的標誌,設定為true
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
//留給子類實現的空方法
initPropertySources();
/**
AbstractPropertyResolver類的requiredProperties是個集合,
在下面的validateRequiredProperties方法中,都要拿requiredProperties中的元素作為key去檢查是否存在對應的環境變數,
如果不存在就丟擲異常
*/
getEnvironment().validateRequiredProperties();
}
上述程式碼中,注意以下兩處:
1. initPropertySources是個空方法,是留給子類實現的,以AnnotationConfigWebApplicationContext類為例,就overwrite了initPropertySources方法:
@Override
protected void initPropertySources() {
ConfigurableEnvironment env = getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(this.servletContext, this.servletConfig);
}
}
跟蹤上面的initPropertySources方法,最終找到了WebApplicationContextUtils.initServletPropertySources:
public static void initServletPropertySources(
MutablePropertySources propertySources, ServletContext servletContext, ServletConfig servletConfig) {
Assert.notNull(propertySources, "propertySources must not be null");
if (servletContext != null && propertySources.contains(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME) &&
propertySources.get(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME) instanceof StubPropertySource) {
propertySources.replace(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME,
new ServletContextPropertySource(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME, servletContext));
}
if (servletConfig != null && propertySources.contains(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME) &&
propertySources.get(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME) instanceof StubPropertySource) {
propertySources.replace(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME,
new ServletConfigPropertySource(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME, servletConfig));
}
}
上面的程式碼所做的事情,就是給context增加環境變數資料(資料來自servlet相關的配置資訊),這樣spring環境就能從context中隨時key取得對應的變量了;
- getEnvironment().validateRequiredProperties()的作用是用來校驗context中是否存在“某些”變數,何謂”某些”?來看validateRequiredProperties方法,追蹤到多層呼叫,最終在AbstractPropertyResolver類的validateRequiredProperties方法中實現:
@Override
public void validateRequiredProperties() {
MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();
for (String key : this.requiredProperties) {
if (this.getProperty(key) == null) {
ex.addMissingRequiredProperty(key);
}
}
if (!ex.getMissingRequiredProperties().isEmpty()) {
throw ex;
}
}
上述程式碼顯示,如果集合requiredProperties中的name在context中找不到對應的變數,就會丟擲異常;
那麼問題來了,requiredProperties集合是何時設定的呢?spring-framework中並沒有呼叫,但是官方的單元測試原始碼給我們了啟發,如下圖:
如上圖紅框,如果業務需要確保某些變數在spring環境中必須存在,就可以呼叫setRequiredProperties方法將變數的name傳遞進去,這樣validateRequiredProperties方法就會做檢查了,我們可以基於現有的各種ApplicationContext實現自己定製一個Context類,確保在validateRequiredProperties方法呼叫之前呼叫setRequiredProperties方法將變數的name傳遞進去(例如重寫initPropertySources),就能讓spring幫我們完成檢查了;
obtainFreshBeanFactory()
接下來看ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();得到臨時變數beanFactory,先看看ConfigurableListableBeanFactory和BeanFactory的關係:
再看看obtainFreshBeanFactory方法:
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//由子類建立beanFactory
refreshBeanFactory();
//取得子類建立好的beanFactory,作為obtainFreshBeanFactory方法的返回值返回
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
上述程式碼中有的refreshBeanFactory需要細看;
refreshBeanFactory方法
refreshBeanFactory方法,在AbstractApplicationContext類中是抽象方法,具體實現在子類中,以其子類AbstractRefreshableApplicationContext為例,我們來看看refreshBeanFactory方法的實現:
@Override
protected final void refreshBeanFactory() throws BeansException {
//如果beanFactory已經存在,就銷燬context管理的所有bean,並關閉beanFactory
if (hasBeanFactory()) {
//其實就是呼叫一些集合的clear方法,解除對一些例項的引用,參考DefaultSingletonBeanRegistry.destroySingletons方法
destroyBeans();
//關閉當前的beanFactory,其實就是將成員變數beanFactory設定為null
closeBeanFactory();
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
- createBeanFactory方法實際上返回的是一個DefaultListableBeanFactory例項:
protected DefaultListableBeanFactory createBeanFactory() {
return new DefaultListableBeanFactory(getInternalParentBeanFactory());
}
2. 接下來的customizeBeanFactory方法是留給子類OverWrite的,該方法的說明和原始碼如下,說明中推薦通過OverWrite的方式對現有beanFactory做特別的設定:
/**
* Customize the internal bean factory used by this context.
* Called for each {@link #refresh()} attempt.
* <p>The default implementation applies this context's
* {@linkplain #setAllowBeanDefinitionOverriding "allowBeanDefinitionOverriding"}
* and {@linkplain #setAllowCircularReferences "allowCircularReferences"} settings,
* if specified. Can be overridden in subclasses to customize any of
* {@link DefaultListableBeanFactory}'s settings.
* @param beanFactory the newly created bean factory for this context
* @see DefaultListableBeanFactory#setAllowBeanDefinitionOverriding
* @see DefaultListableBeanFactory#setAllowCircularReferences
* @see DefaultListableBeanFactory#setAllowRawInjectionDespiteWrapping
* @see DefaultListableBeanFactory#setAllowEagerClassLoading
*/
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
if (this.allowBeanDefinitionOverriding != null) {
//allowBeanDefinitionOverriding表示是否允許註冊一個同名的類來覆蓋原有類(注意是類,不是例項)
beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.allowCircularReferences != null) {
//allowCircularReferences表示是否執行多個類之間的迴圈引用
beanFactory.setAllowCircularReferences(this.allowCircularReferences);
}
}
3. loadBeanDefinitions在AbstractRefreshableApplicationContext類中是個抽象方法,留給子類實現,作用是把所有bean的定義後儲存在context中,以AbstractXmlApplicationContext為例,看看loadBeanDefinitions方法做了什麼:
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
以上程式碼可見,載入bean的定義是通過XmlBeanDefinitionReader 來完成的,重點關注loadBeanDefinitions方法:
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
上述程式碼中的getConfigResources()和getConfigLocations(),究竟哪個會返回值有效資料呢?這就要去看ClassPathXmlApplicationContext的構造方法了:
//這個方法設定的是configLocations
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
//這個方法設定的是這個方法設定的是configResources
public ClassPathXmlApplicationContext(String[] paths, Class<?> clazz, ApplicationContext parent)
throws BeansException {
super(parent);
Assert.notNull(paths, "Path array must not be null");
Assert.notNull(clazz, "Class argument must not be null");
this.configResources = new Resource[paths.length];
for (int i = 0; i < paths.length; i++) {
this.configResources[i] = new ClassPathResource(paths[i], clazz);
}
refresh();
}
因此,到底是configLocations 還是configResources ,和我們使用哪個構造方法來例項化applicationContext物件有關;
4. 如果我們例項化applicationContext物件的方式是new ClassPathXmlApplicationContext(“applicationContext.xml”),那麼setConfigLocations方法就會被呼叫,因此loadBeanDefinitions方法內部,實際執行的程式碼如下:
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
5. 現在可以來看AbstractBeanDefinitionReader類的loadBeanDefinitions(String… locations)方法了:
public int loadBeanDefinitions(String... locations) throws BeanDefinitionStoreException {
Assert.notNull(locations, "Location array must not be null");
int counter = 0;
for (String location : locations) {
counter += loadBeanDefinitions(location);
}
return counter;
}
展開上面for迴圈中呼叫的方法:
public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
ResourceLoader resourceLoader = getResourceLoader();
if (resourceLoader == null) {
throw new BeanDefinitionStoreException(
"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
}
if (resourceLoader instanceof ResourcePatternResolver) {
// Resource pattern matching available.
try {
Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
int loadCount = loadBeanDefinitions(resources);
if (actualResources != null) {
for (Resource resource : resources) {
actualResources.add(resource);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
}
return loadCount;
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"Could not resolve bean definition resource pattern [" + location + "]", ex);
}
}
else {
// Can only load single resources by absolute URL.
Resource resource = resourceLoader.getResource(location);
int loadCount = loadBeanDefinitions(resource);
if (actualResources != null) {
actualResources.add(resource);
}
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
}
return loadCount;
}
}
以上方法中,首先要記得resourceLoader是ClassPathXmlApplicationContext(beanDefinitionReader.setResourceLoader(this)這行程式碼),所有resourceLoader.getResource(location)這行程式碼最終會呼叫PathMatchingResourcePatternResolver類的getResources(String locationPattern)方法得到bean有關的Resource物件;
得到Resource物件後,接著會呼叫loadBeanDefinitions(Resource… resources)方法來載入bean的定義了,最終是呼叫XmlBeanDefinitionReader.loadBeanDefinitions(EncodedResource encodedResource)方法:
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource.getResource());
}
Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
if (currentResources == null) {
currentResources = new HashSet<EncodedResource>(4);
this.resourcesCurrentlyBeingLoaded.set(currentResources);
}
if (!currentResources.add(encodedResource)) {
throw new BeanDefinitionStoreException(
"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
}
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}
finally {
inputStream.close();
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(
"IOException parsing XML document from " + encodedResource.getResource(), ex);
}
finally {
currentResources.remove(encodedResource);
if (currentResources.isEmpty()) {
this.resourcesCurrentlyBeingLoaded.remove();
}
}
}
上述程式碼可見,重要的是通過Resource物件得到InputStream,再呼叫doLoadBeanDefinitions方法:
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}
...
上面是載入bean定義的關鍵程式碼:先製作Document物件,再呼叫registerBeanDefinitions方法,最終會將每個bean的定義放入DefaultListableBeanFactory的beanDefinitionMap中,詳細的堆疊如下圖:
完成了bean定義的註冊,可以回到AbstractRefreshableApplicationContext.refreshBeanFactory方法了,看看loadBeanDefinitions(beanFactory)之後的程式碼:
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
至此,refreshBeanFactory方法分析完畢,該方法所做的事情:把xml檔案中的bean定義被解析後,存放在DefaultListableBeanFactory的beanDefinitionMap中;
現在回到主線的AbstractApplicationContext.refresh()方法內,obtainFreshBeanFactory()我們已經分析完畢,所有bean定義都被存放在beanFactory這個臨時變數對應的例項中;
prepareBeanFactory
接下來是prepareBeanFactory(beanFactory),看一下此方法的原始碼:
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
//設定類載入器
beanFactory.setBeanClassLoader(getClassLoader());
//設定解析器,用於解析bean的定義中出現的Spel表示式表示式
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
//設定一個註冊介面,該介面只有一個方法registerCustomEditors,用來設定自定義的轉換器
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// 部署一個bean的後置處理器ApplicationContextAwareProcessor,用於將spring的環境資訊注入到例項化的bean之中
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//bean在初始化的時候,如果有屬性的型別為ResourceLoaderAware,則該屬性不會被依賴注入
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
//bean如果有個屬性的型別為BeanFactory.class,那麼該屬性會被設定為beanFactory
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
// 部署一個bean的後置處理器ApplicationContextAwareProcessor,用於AOP靜態代理相關的處理
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
//註冊一個bean
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
上述程式碼中有以下幾點需要注意:
1. beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment())),此方法要配合AbstractBeanFactory.registerCustomEditors方法一起看更好理解:addPropertyEditorRegistrar方法向propertyEditorRegistrars屬性中放入了一個registrar,之後呼叫registerCustomEditors方法的時候,會用到propertyEditorRegistrars中的registrar,呼叫這些registrar的registerCustomEditors方法,完成自定義的轉換器的設定;
2. beanFactory.addBeanPostProcessor方法用來注入後置處理器,在bean例項被建立後,初始化方法被執行的前後,後置處理器的postProcessBeforeInitialization、postProcessAfterInitialization這兩個方法會分別被呼叫;
3. beanFactory.ignoreDependencyInterface設定了依賴注入時要忽略的介面,例如bean有個屬性型別是ResourceLoaderAware,那麼該屬性不會被注入ResourceLoaderAware型別的例項;
4. beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory)是特殊設定,如果一個bean有個屬性的型別是BeanFactory,那麼該屬性會被設定為beanFactory這個例項;
總的來說prepareBeanFactory方法就是為beanFactory做一些設定工作,傳入一些後面會用到的引數和工具類,再在spring容器中建立一些bean;
postProcessBeanFactory
postProcessBeanFactory方法是留給子類擴充套件的,可以在bean例項初始化之前註冊後置處理器(類似prepareBeanFactory方法中的beanFactory.addBeanPostProcessor),以子類AbstractRefreshableWebApplicationContext為例,其postProcessBeanFactory方法如下:
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
}
可見除了WebApplicationContextUtils類的工作之外,其餘的都是和prepareBeanFactory方法中類似的處理;
invokeBeanFactoryPostProcessors
invokeBeanFactoryPostProcessors方法用來執行BeanFactory例項的後置處理器BeanFactoryPostProcessor的postProcessBeanFactory方法,這個後置處理器除了原生的,我們也可以自己擴充套件,用來對Bean的定義做一些修改,由於此時bean還沒有例項化,所以不要在自己擴充套件的BeanFactoryPostProcessor中呼叫那些會觸發bean例項化的方法(例如BeanFactory的getBeanNamesForType方法),原始碼的文件中有相關說明,如下圖紅框所示,不要觸發bean的例項化,如果要處理bean例項請在BeanPostProcessor中進行;:
registerBeanPostProcessors
registerBeanPostProcessors方法的程式碼略多,就不在此貼出來了,簡單的說,就是找出所有的bean的後置處理器(注意,是bean的後置處理器,不是beanFactory的後置處理器,bean後置處理器處理的是bean例項,beanfactory後置處理器處理的是bean的定義),然後將這些bean的後置處理器分為三類:
1. 實現了順序介面Ordered.class的,先放入orderedPostProcessors集合,排序後順序加入beanFactory的bean後處理集合中;
2. 既沒有實現Ordered.class,也沒有實現PriorityOrdered.class的後置處理器,也加入到beanFactory的bean後處理集合中;
3. 最後是實現了優先順序介面PriorityOrdered.class的,排序後順序加入beanFactory的bean後處理集合中;
registerBeanPostProcessors方法執行完畢後,beanFactory中已經儲存了有序的bean後置處理器,在bean例項化之後,會依次使用這些後置處理器對bean例項來做對應的處理;
initMessageSource
initMessageSource方法用來準備國際化資源相關的,將實現了MessageSource介面的bean存放在ApplicationContext的成員變數中,先看是否有配置,如果有就例項化,否則就建立一個DelegatingMessageSource例項的bean;
initApplicationEventMulticaster
spring中有事件、事件廣播器、事件監聽器等組成事件體系,在initApplicationEventMulticaster方法中對事件廣播器做初始化,如果找不到此bean的配置,就建立一個SimpleApplicationEventMulticaster例項作為事件廣播器的bean,並且儲存為applicationContext的成員變數applicationEventMulticaster;
onRefresh
onRefresh是個空方法,留給子類自己實現的,在例項化bean之前做一些ApplicationContext相關的操作,以子類AbstractRefreshableWebApplicationContext為例,看看它的onRefresh方法:
@Override
protected void onRefresh() {
this.themeSource = UiApplicationContextUtils.initThemeSource(this);
}
可見是做了主題相關的初始化,並儲存在ApplicationContext的成員變數中;
registerListeners
方法名為registerListeners,看名字像是將監聽器註冊在事件廣播器中,但實際情況並非如此,只有一些特殊的監聽器被註冊了,那些在bean配置檔案中實現了ApplicationListener介面的類還沒有例項化,所以此處只是將其name儲存在廣播器中,將這些監聽器註冊在廣播器的操作是在bean的後置處理器中完成的,那時候bean已經例項化完成了,我們看程式碼:
protected void registerListeners() {
// 註冊的都是特殊的事件監聽器,而並非配置中的bean
for (ApplicationListener<?> listener : getApplicationListeners()) {
getApplicationEventMulticaster().addApplicationListener(listener);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let post-processors apply to them!
// 根據介面型別找出所有監聽器的名稱
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
// 這裡只是把監聽器的名稱儲存在廣播器中,並沒有將這些監聽器例項化!!!
getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
}
finishBeanFactoryInitialization
finishBeanFactoryInitialization方法做了兩件事:
1. beanFactory物件的初始化;
2. 我們在bean配置檔案中配置的那些單例的bean,都是在finishBeanFactoryInitialization方法中例項化的;
看程式碼:
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
// 例項化型別轉換的bean,並儲存在ApplicationContext中
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));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
// 例項化LoadTimeWeaverAware介面的bean,用於ApsectJ的類載入期織入的處理
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
// 確保臨時的classLoader為空,臨時classLoader一般被用來做型別匹配的
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
// 將一個標誌設定為true,表示applicationContext已經快取了所有bean的定義,這些bean的name都被儲存在applicationContext的frozenBeanDefinitionNames成員變數中,相當於一個快照,記錄了當前那些bean的定義已經拿到了
beanFactory.freezeConfiguration();
// 例項化所有還未例項化的單例bean
beanFactory.preInstantiateSingletons();
}
上述程式碼中,beanFactory.preInstantiateSingletons()需要展開仔細看:
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("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.
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
// 獲取bean的定義,該定義已經和父類定義做了合併
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 非抽象類、是單例、非懶載入
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//FactoryBean的處理
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
//非FactoryBean的例項化、初始化
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
// 單例例項化完成後,如果實現了SmartInitializingSingleton介面,afterSingletonsInstantiated就會被呼叫,此處用到了特權控制邏輯AccessController.doPrivileged
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
smartSingleton.afterSingletonsInstantiated();
return null;
}
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
上述程式碼中,要重點關注getBean(beanName),這裡面會例項化bean,由於內容太多不適合在本章細說,這裡先將例項化bean的呼叫路徑整理出來:
AbstractBeanFactory.getBean(String name)
->
AbstractBeanFactory.doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
->
DefaultSingletonBeanRegistry.getSingleton(String beanName, ObjectFactory<?> singletonFactory)
->
AbstractBeanFactory.doGetBean中的匿名類的getObject方法
->
AbstractAutowireCapableBeanFactory.createBean(String beanName, RootBeanDefinition mbd, Object[] args)
->
AbstractAutowireCapableBeanFactory.doCreateBean(final String beanName, final RootBeanDefinition mbd, Object[] args)
->
AbstractAutowireCapableBeanFactory.createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args)
->
instantiateBean(final String beanName, final RootBeanDefinition mbd)
->
SimpleInstantiationStrategy.instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner)
->
BeanUtils.instantiateClass(Constructor<T> ctor, Object... args)
->
Constructor.newInstance(Object ... initargs)
->
bean的構造方法
以上呼叫路徑可以看出,bean物件的建立是BeanUtils.instantiateClass方法通過反射來建立的;
再來看看bean的成員變數是什麼時候被注入值的,如下圖,AbstractAutowireCapableBeanFactory.doCreateBean方法中,先呼叫createBeanInstance建立bean的物件(綠框所示),再呼叫populateBean方法給成員變數注入內容(紅框所示):
將注入值的呼叫堆疊整理如下,可見是也是通過反射完成注入的:
AbstractAutowireCapableBeanFactory.populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw)
->
AbstractAutowireCapableBeanFactory.applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs)
->
AbstractPropertyAccessor.setPropertyValues(PropertyValues pvs)
->
BeanWrapperImpl.setPropertyValue(PropertyValue pv)
->
Method.invoke(Object obj, Object... args)
看過了成員變數注入的邏輯後,還有個重要的邏輯也請關注,就是bean的初始化(bean的配置檔案中的init-method屬性),AbstractAutowireCapableBeanFactory.doCreateBean方法中,在呼叫populateBean方法給成員變數注入值之後,馬上呼叫initializeBean方法進行初始化操作,呼叫堆疊整理如下:
AbstractAutowireCapableBeanFactory.initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd)
->
AbstractAutowireCapableBeanFactory.invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
->
AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd)
->
Method.invoke(Object obj, Object... args)
可見依舊是通過反射來執行初始化方法;
finishRefresh
最後一個方法是finishRefresh,這是在bean的例項化、初始化等完成後的一些操作,例如生命週期變更的回撥,傳送applicationContext重新整理完成的廣播等,展開看看:
protected void finishRefresh() {
// 檢查是否已經配置了生命週期處理器,如果沒有就new一個DefaultLifecycleProcessor
initLifecycleProcessor();
// 找到所有實現了Lifecycle介面的bean,按照每個bean設定的生命週期階段進行分組,再依次呼叫每個分組中每個bean的start方法,完成生命週期監聽的通知
getLifecycleProcessor().onRefresh();
// 建立一條代表applicationContext重新整理完成的事件,交給廣播器去廣播
publishEvent(new ContextRefreshedEvent(this));
// 如果配置了MBeanServer,就完成在MBeanServer上的註冊
LiveBeansView.registerApplicationContext(this);
}
至此,整個初始化流程咱們已經過了一遍了,但是篇幅有限,很多細節都沒有展開,另外很多子類也有自己獨特的擴充套件,這些都需要花時間去細看,希望本文能幫您整理思路,從總體上了解初始化的各個關鍵步驟,以免過早陷入細節;