内容简介：Spring源码教程02--Spring的IoC容器分析
上一节 “[原创]Spring教程01--Spring开始篇_Helloworld” 中简单的介绍SpringFramwork的简单使用；通过Helloworld的程序做演示，本节将继续解读Spring的Ioc容器实现和分析。
Spring IoC容器启动过程
Spring的IoC容器启动大致分为下面的三个步骤： Resource定位 、 Resoure的载入 、 Resoured的注册 三个步骤；下面使用xml文件配置方式显示的配置方式步骤：
首先看下ApplicationContext的构造方法定义：
public FileSystemXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
//设置Context
super(parent);
//读取XML等配置文件定位
setConfigLocations(configLocations);
//创建BeanFactory的关键[重点]
if (refresh) {
refresh();
}
}
@Override
//这个refresh()启动容器[重要的放在首位]
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
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 factory processors registered as beans in the context.
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.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}
Resource定位
为了便于理解；提前解析了Context的属性如下：
| 对象名 | 类 型 | 作 用 | 归属类 |
|---|---|---|---|
| configResources | Resource[] | 配置文件资源对象数组 | ClassPathXmlApplicationContext |
| configLocations | String[] | 配置文件字符串数组，存储配置文件路径 | AbstractRefreshableConfigApplicationContext |
| beanFactory | DefaultListableBeanFactory | 上下文使用的Bean工厂 | AbstractRefreshableApplicationContext |
| beanFactoryMonitor | Object | Bean工厂使用的同步监视器 | AbstractRefreshableApplicationContext |
| id | String | 上下文使用的唯一Id，标识此ApplicationContext | AbstractApplicationContext |
| parent | ApplicationContext | 父级ApplicationContext | AbstractApplicationContext |
| beanFactoryPostProcessors | List | 存储BeanFactoryPostProcessor接口，Spring提供的一个扩展点 | AbstractApplicationContext |
| startupShutdownMonitor | Object | refresh方法和destory方法公用的一个监视器，避免两个方法同时执行 | AbstractApplicationContext |
| shutdownHook | Thread | Spring提供的一个钩子，JVM停止执行时会运行Thread里面的方法 | AbstractApplicationContext |
| resourcePatternResolver | ResourcePatternResolver | 上下文使用的资源格式解析器 | AbstractApplicationContext |
| lifecycleProcessor | LifecycleProcessor | 用于管理Bean生命周期的生命周期处理器接口 | AbstractApplicationContext |
| messageSource | MessageSource | 用于实现国际化的一个接口 | AbstractApplicationContext |
| applicationEventMulticaster | ApplicationEventMulticaster | Spring提供的事件管理机制中的事件多播器接口 | AbstractApplicationContext |
| applicationListeners | Set | Spring提供的事件管理机制中的应用监听器 | AbstractApplicationContext |
1）设置存储配置文件路径
AbstractRefreshableConfigApplicationContext 的 setConfigLocations() 方法确定其文件的位置；代码比较简单。
public void setConfigLocations(@Nullable String... locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
在上面的过程；我们获取配置文件的路径内容。下面看看具体的IoC容器的创建的具体过程了。
2）加载配置文件的路径
（1）创建BeanFactory
@Override
protected final void refreshBeanFactory() throws BeansException {
if (hasBeanFactory()) {
destroyBeans();
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);
}
}
（2）读取文件配置 这个中间调用过程省略了；直接看结果：这里直接看log日志结果我们不用说太多了...
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<>(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());
}
//下面开始解析XML方法
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();
}
}
}
Resource的载入
下面我们接着根据路径配置，读取到内存中；采用SAX文件的解析；看源码：
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
...
try {
Document doc = doLoadDocument(inputSource, resource);
//解析xml文件注册JavaBean
return registerBeanDefinitions(doc, resource);
}
...
//省略catch()代码...
Resouce文件的解析
protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isInfoEnabled()) {
logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
preProcessXml(root);
//重点代码：注册JavaBean
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
其实写到这里感觉大家有兴趣的可以继续看看这个；如何读取xml文件如理 <bean> 等标签的操作...这里我推荐一片文章吧： Spring解密 - XML解析 与 Bean注册 ；后面写的比较具体。截止到目前通过XML解析；将配置文件读取到BeanDefine中；下面看看如何将其注册到IoC容器。
注册IoC容器
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
Assert.hasText(beanName, "Bean name must not be empty");
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
//将获取BeanName和之前解析BeanDefine放入Map集合中从而完成注册
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
上面的源码中我们呢需要关注 this.beanDefinitionMap.put(beanName, beanDefinition); 这句代码；这个Bean注入BeanDefineMap中；到此这里已经完成了IoC容器的初始化。
到这里基本已经结束了； ApplicationContext application = new ClassPathXmlApplicationContext("applicationContext.xml"); 这样一句代码其实；也写了一章节；其实如果你是看着篇文章可以参考我的方法堆栈进行阅读。最后文章的部分其实源都简明的展示给你；后期我希望可以使用更多图展示给大家。
参考资料：
- 《Spring技术内幕》
- Spring-IOC核心源码学习
- 【Spring源码分析】Bean加载流程概览
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持 码农网
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