Spring Bean加载过程
1、找准入口，使用ClassPathXmlApplicationContext的构造方法加载配置文件，用于加载classPath下的配置文件
//第一行，执行完成之后就完成了spring配置文件的加载，刷新spring上下文
ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext(
"classpath:spring-mvc.xml");
//获取实例Bean
Person person=context.getBean("person",Person.class);2、ClassPathXmlApplicationContext构造方法源码如下：
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
//设置父级的ApplicationContext，null
super(parent);
//1.设置配置文件的路径， 2. 将路径中的占位符${placeholder}使用系统的变量替换
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}3、主要方法为setConfigLocation(configLocation),这个方法调用其父类AbstractRefreshableConfigApplicationContext中的方法
//locations : 配置文件路径
public void setConfigLocations(String[] locations) {
if (locations != null) {
//断言
Assert.noNullElements(locations, "Config locations must not be null");
//存储配置文件路径的数组，存储去掉占位符后的文件路径数组
this.configLocations = new String[locations.length];
//遍历locations，解析占位符
for (int i = 0; i < locations.length; i++) {
//调用resolvePath解析占位符
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}4、进入resovePath的源码，实际上执行的是AbstractPropertyResolver的doResolverPlaceholders方法
/**
* text : 需要解析的路径
* PropertyPlaceholderHelper ： 这个是解析系统占位符的辅助类，主要用来将占位符替换成系统的环境变量
*/
private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {
//调用PropertyPlaceholderHelper类中的replacePlaceholders方法
return helper.replacePlaceholders(text, new PropertyPlaceholderHelper.PlaceholderResolver() {
public String resolvePlaceholder(String placeholderName) {
return getPropertyAsRawString(placeholderName);
}
});
}5、进入PropertyHelper的replacePlaceholder方法，实际上调用PropertyPlaceholderHelper的parseStringValue解析占位符
public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
Assert.notNull(value, "Argument 'value' must not be null.");
//调用的是parseStringValue方法
return parseStringValue(value, placeholderResolver, new HashSet());
}
/**
* strVal ： 需要解析的字符串，就是配置文件的路径
* placeholderResolver ： 策略接口，占位符解析器
* visitedPlaceholders ： 存储已经访问过的占位符
**/
protected String parseStringValue(
String strVal, PlaceholderResolver placeholderResolver, Set visitedPlaceholders) {
//将strval转换成StringBuilder，便于后续到操作
StringBuilder buf = new StringBuilder(strVal);
//this.placeholderPrefix这个是占位符的前缀 ${,在创建PropertyHelper的时候就已经指定了占位符的placeholderPrefix="${" ,placeholderSuffix="}",valueSeparator=":"
//获取前缀在这个配置文件路径中的开始索引
int startIndex = strVal.indexOf(this.placeholderPrefix);
while (startIndex != -1) {
//占位符前缀在路径中的结束索引
int endIndex = findPlaceholderEndIndex(buf, startIndex);
//如果结束索引存在
if (endIndex != -1) {
//此时取出${plcaeholder}中的占位符内容placeholder
String placeholder = buf.substring(startIndex + this.placeholderPrefix.length(), endIndex);
//保存取出来的占位符内容placeholder
String originalPlaceholder = placeholder;
//如果占位符中的内容已经被访问过了，抛出出异常返回，递归结束的条件
if (!visitedPlaceholders.add(originalPlaceholder)) {
throw new IllegalArgumentException(
"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
}
//递归解析已经取出的占位符中的内容 palceholder
placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
//这个最重要的一步，将解析占位符内容placeholder的值，比如将java.version转换成1.8.0_60
String propVal = placeholderResolver.resolvePlaceholder(placeholder);
if (propVal == null && this.valueSeparator != null) {
int separatorIndex = placeholder.indexOf(this.valueSeparator);
if (separatorIndex != -1) {
String actualPlaceholder = placeholder.substring(0, separatorIndex);
String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
if (propVal == null) {
propVal = defaultValue;
}
}
}
//如果解析出来的占位符不为空，比如${java.version}将被解析成 1.8.0_60
if (propVal != null) {
//此时继续递归解析出1.8.0_60中的占位符
propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
//将路径中的占位符替换成系统变量的值，比如将${java.version} 替换成 1.8.0_60
buf.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
if (logger.isTraceEnabled()) {
logger.trace("Resolved placeholder '" + placeholder + "'");
}
//继续在路径字符串中剩余的子串中查找占位符，如果有占位符，那么还会继续解析占位符
startIndex = buf.indexOf(this.placeholderPrefix, startIndex + propVal.length());
}
else if (this.ignoreUnresolvablePlaceholders) {
// Proceed with unprocessed value.
startIndex = buf.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
}
else {
throw new IllegalArgumentException("Could not resolve placeholder '" +
placeholder + "'" + " in string value \"" + strVal + "\"");
}
//将已转换成功的占位符从以访问的集合中移除即可
visitedPlaceholders.remove(originalPlaceholder);
}
else {
startIndex = -1;
}
}
return buf.toString(); //将解析完成之后的配置文件返回
} 6、然后是ClassPathXmlApplicationContext中的refresh方法，实际上调用的是父类AbstractApplicationContext的方法
//刷新spring上下文
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//在刷新之前设置一些参数，比如设置开始时间戳，上下文是否激活的标志，输出刷新上下文的信息，验证一些必要的属性
prepareRefresh();
//需要创建beanFactory，如果已经存在beanFactory，那么关闭，详细其请看 10
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 准备上下文工厂，详情见12
prepareBeanFactory(beanFactory);
try {
//允许子类向后置处理器添加组件
postProcessBeanFactory(beanFactory);
// 调用BeanFactoryPostProcessor和BeanDefintionRegistoryPostProcessor这两个后置处理器
invokeBeanFactoryPostProcessors(beanFactory);
// 注册BeanPostProcessor,用来拦截bean的创建，详情见 14
registerBeanPostProcessors(beanFactory);
//初始化消息源
initMessageSource();
// 初始化应用程序事件广播器，用户可以自定义一个事件广播器，如果用户没有定义，那么使用默认的事件广播器SimpleApplicationEventMulticaster
initApplicationEventMulticaster();
// 在其他子类中初始化bean
onRefresh();
// 检测事件监听器
registerListeners();
//完成实例化剩余的单例(non-lazy-init)
finishBeanFactoryInitialization(beanFactory);
// 完成刷新，初始化生命周期处理器......
finishRefresh();
}
catch (BeansException ex) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
}
}7、进入obtainFreshBeanFactory方法
//AbastractApplicationContext的方法
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//实际刷新上下文的方法，这个方法就是实际的刷新上下文方法，其中会调用loadBeanDefinitions(beanFactory);加载配置文件中的内容到BeanDefiniton中
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
//org.springframework.context.support.AbstractRefreshableApplicationContext中的方法
//AbstractApplicationContext的子类中的方法
@Override
protected final void refreshBeanFactory() throws BeansException {
//如果其中有beanfactory，那么销毁
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//重新创建一个beanFactory
DefaultListableBeanFactory beanFactory = createBeanFactory();
//设置序列化id
beanFactory.setSerializationId(getId());
//定制beanFactory，设置相关属性，包括是否允许覆盖名称的不同定义的对象及循环依赖以及
//设置@Autowired和@Qualifier，注解解析器QualifierAnnotationAutowireCandidateResolver
customizeBeanFactory(beanFactory);
//加载BeanDefine 详情见 11
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}8、进入loadBeanDefinitions(beanFactory)方法
//这个是org.springframework.context.support.AbstractXmlApplicationContext类中的方法
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//创建要给beanDefinitionReader，用于读取BeanDefinition
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
//配置XmlBeanDefinitionReader
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
initBeanDefinitionReader(beanDefinitionReader);
//加载BeanDefiniton，主要的功能从配置文件中读取BeanDefiniton注册到注册表中
loadBeanDefinitions(beanDefinitionReader);
}9、prepareBeanFactory:准备BeanFactory
//准备BeanFactory，设置一些参数，比如后置处理器，
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
//设置类加载器
beanFactory.setBeanClassLoader(getClassLoader());
//设置表达式解析器，用来解析BeanDefiniton中的带有表达式的值
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// 配置后置处理器，主要的作用就是在spring实例化bean的前后做一些操作
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
//忽略自动装配的类，这些类都不能使用@Resource或者@Autowired自动装配获取对象
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
//注册可解析的自动装配类
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
//在添加一个应用程序监听器
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
//检查这些类是否被
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// 将下面这些类注册到容器中，使用registerSingleton方法注册，我们可以直接从容器中获取这些类的对象使用
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
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());
}
}10、调用BeanFactory的后置处理器，主要的功能就是调用注册在容器中的BeanFactoryPostProcessor和BeanDefinitionRegistoryPostProcessor
//实例化和调用BeanFactory后置处理器，必须在单例实例化之前调用
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
//调用后置处理器注册委托类的方法调用，getBeanFactoryPostProcessors用于获取注册的全部的BeanFactoryPostProcessor
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
}
//实际的调用方法，PostProcessorRegistrationDelegate中的方法
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set processedBeans = new HashSet();
//如果beanFactory是BeanDefinitionRegistry的子类，BeanDefinitionRegistry使用来向注册表中注册Bean的元信息的(BeanDefintion)
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
//存放BeanFactoryPostProcessor
List regularPostProcessors = new LinkedList();
//存放BeanDefinitionRegistryPostProcessor
List registryPostProcessors =
new LinkedList();
//遍历。判断是否是BeanDefinitionRegistryPostProcessor实例
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryPostProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
//调用BeanDefinitionRegistryPostProcessor
registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
//添加
registryPostProcessors.add(registryPostProcessor);
}
else {
//表示这个是BeanFactoryPostProcessor实例，添加进集合
regularPostProcessors.add(postProcessor);
}
}
//--- 根据类型类型获取beanFactory中注册的BeanDefinitionRegistryPostProcessor的bean的所有名称数组
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
// ---- 首先调用的是BeanDefinitionRegistryPostProcessor类型的后置处理器
//存放实现PriorityOrdered这个接口的BeanDefinitionRegistryPostProcessor
List priorityOrderedPostProcessors = new ArrayList();
//遍历，如果实现了PriorityOrdered这个接口就保存下来
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
//按照优先级排序
OrderComparator.sort(priorityOrderedPostProcessors);
//添加进入集合
registryPostProcessors.addAll(priorityOrderedPostProcessors);
//首先调用实现PriorityOrdered这个接口的BeanDefinitionRegistryPostProcessor
invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);
// ---- 下面是调用实现Orderd这个接口的BeanDefinitionRegistryPostProcessor
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
List orderedPostProcessors = new ArrayList();
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
OrderComparator.sort(orderedPostProcessors);
registryPostProcessors.addAll(orderedPostProcessors);
invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);
// ---- 最终调用剩余全部的BeanDefinitionRegistryPostProcessor
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
registryPostProcessors.add(pp);
processedBeans.add(ppName);
pp.postProcessBeanDefinitionRegistry(registry);
reiterate = true;
}
}
}
// 调用BeanFactoryPostProcessor接口中的方法，因为BeanDefitionRegistory继承了这个接口
invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
//--- 下面是调用实现BeanFactoryPostProcessor接口的类，和上面的流程一样
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List priorityOrderedPostProcessors = new ArrayList();
List orderedPostProcessorNames = new ArrayList();
List nonOrderedPostProcessorNames = new ArrayList();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
OrderComparator.sort(priorityOrderedPostProcessors);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List orderedPostProcessors = new ArrayList();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
OrderComparator.sort(orderedPostProcessors);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List nonOrderedPostProcessors = new ArrayList();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
} 11、注册BeanPostProcessor，用来拦截Bean的创建，这个接口可以实现在Bean初始化和初始化之后执行相关的操作
//依然这里依然调用的PostProcessorRegistrationDelegate，其中包含了注册后置处理器和调用后置处理器的方法，相当于一个代理人
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}
//PostProcessorRegistrationDelegate中的注册BeanPostProcessors的方法
//其中beanFactory这个新创建的beanFactory，其中的BeanPostProcessor都没有注册，applicationContext这个是之前创建的，其中的处理器已经注册过了
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
//根据类型新加载全部的BeanFactoryProcessor的类，
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
//创建BeanPostProcessor检测器
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List priorityOrderedPostProcessors = new ArrayList();
List internalPostProcessors = new ArrayList();
List orderedPostProcessorNames = new ArrayList();
List nonOrderedPostProcessorNames = new ArrayList();
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
OrderComparator.sort(priorityOrderedPostProcessors);
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
List orderedPostProcessors = new ArrayList();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
OrderComparator.sort(orderedPostProcessors);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
List nonOrderedPostProcessors = new ArrayList();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
OrderComparator.sort(internalPostProcessors);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}