Spring 容器初始化
初始化代码
@Test
public void testInit2(){
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:beans.xml");
Car car= (Car) context.getBean("car");
System.out.println(car.getBrand());
}
ClassPathXmlApplicationContext代码结构图
SpringIOC容器初始化代码结构图
ClassPathXmlApplicationContext初始化代码
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
//解析配置文件，例如（多个配置文件路径解析成字符串数组，将路径前后的空格去掉）
setConfigLocations(configLocations);
if (refresh) {
//Spring IOC容器初始化的核心方法
refresh();
}
}
核心方法refresh()代码解析
public void refresh() throws BeansException, IllegalStateException {
//此处增加Synchronized字段，给容器refresh加锁，避免容器处在refresh阶段时，容器进行了初始化或者销毁的操作
synchronized (this.startupShutdownMonitor) {
//refresh容器时的一些准备工作，设置容器的状态(close设置为false，active设置为true)
prepareRefresh();
//重点方法：
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//准备 Bean 容器: prepareBeanFactory
prepareBeanFactory(beanFactory);
try {
// 允许子类这册子自定义的后置处理器
postProcessBeanFactory(beanFactory);
// 调用子类的后置处理器
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;
}
}
}
obtainFreshBeanFactory()方法解析【refresh中核心方法】
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//如果有旧的BeanFactory则销毁旧的BeanFactory，然后创建一个新的BeanFactory，加载Bean、注册Bean等等
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
//refreshBeanFactory()方法代码解析
protected final void refreshBeanFactory() throws BeansException {
//如果有BeanFactory，销毁和关闭BeanFactory
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//创建一个DefaultListableBeanFactory对象
DefaultListableBeanFactory beanFactory = createBeanFactory();
//设置beanFactory的的序列化ID
beanFactory.setSerializationId(getId());
//定义BeanFactory的属性(Bean可覆盖，Bean循环引用)
customizeBeanFactory(beanFactory);
//加载Bean
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
BeanDefinition 的覆盖问题可能会有开发者碰到这个坑，就是在配置文件中定义 bean 时使用了相同的 id 或 name，默认情况下，allowBeanDefinitionOverriding 属性为 null，如果在同一配置文件中重复了，会抛错，但是如果不是同一配置文件中，会发生覆盖
为什么使用DafaultListableBeanFactory初始化BeanFactory
BeanFactory代码结构
从上图可以看出DefaultListableBeanFactory类和所有的BeanFactory类或者接口都有关系，因此这个类是最强大的BeanFactory。
加载 Bean: loadBeanDefinitions。这个方法根据配置加载各个Bean，然后将Bean放置到BeanFactory中。读取配置的操作在 XmlBeanDefinitionReader 中，其负责加载配置、解析。
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// 为BeanFacotry创建一个获取Bean信息的XmlBeanDefinitionReader对象
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
//给XmlBeanDefinitionReader配置上下文的资源环境
beanDefinitionReader.setEnvironment(this.getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
//允许子类提供自定义初始化BeanFactory的reader
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
//初始化加载Bean definitions的Reader，默认的实现是空的(让子类提供定制的初始化)
initBeanDefinitionReader(beanDefinitionReader);
//加载BeanDefinitionReader
loadBeanDefinitions(beanDefinitionReader);
}
加载BeanDefinitionReader的加载方法loadBeanDefinitions
/**
*通过XmlBeanDefinitionReader加载bean definitions,bean *factory的生命周期通过refreshBeanFactory方法来处理。这个方法应该来加*载或者注册bean definitions
*/
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
//以Resources的方式获取配置文件的资源位置
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
//以String的形式获取配置文件的位置
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
无论是上面获取的是Resource还是String形式的资源地址，最后加载资源的加载方法都是下面的loadBeanDefinitions方法
/**
* 从特别的xml文件来加载bean definition
*/
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());
}
//用ThreadLocal来存放当前的资源
Set 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 {
//将Resource转换成XML实体的单一输入源InputSource
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//处理InputSource的方法
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();
}
}
}
处理inputSource的doLoadBeanDefinitions方法
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//将inputSource转换成Document对象
Document doc = doLoadDocument(inputSource, resource);
//下面方法是对BeanDefinition解析的详细过程，这个解析会使用到Spring的Bean配置规则
return registerBeanDefinitions(doc, resource);
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (SAXParseException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
}
catch (SAXException ex) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(),
"XML document from " + resource + " is invalid", ex);
}
catch (ParserConfigurationException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Parser configuration exception parsing XML from " + resource, ex);
}
catch (IOException ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"IOException parsing XML document from " + resource, ex);
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(resource.getDescription(),
"Unexpected exception parsing XML document from " + resource, ex);
}
}
加载Spring Bean的方法registerBeanDefinitions解析
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//这里得到BeanDefinitionDocumentReader来对XML的BeanDefinition进行解析
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
documentReader.setEnvironment(getEnvironment());
int countBefore = getRegistry().getBeanDefinitionCount();
//具体的解析过程在这个registerBeanDefinitions中完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
/**
*根据Spring-beans的XSD来解析bean definitions
*/
@Override
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
//从xml根节点来解析
doRegisterBeanDefinitions(root);
}
/**
*
* 通过给定的root来注册每个定义的bean
*/
protected void doRegisterBeanDefinitions(Element root) {
//通过BeanDefinitionParserDelegate类来解析Bean定义
BeanDefinitionParserDelegate parent = this.delegate;
//这里为什么要定义一个 parent? 看到后面就知道了，是递归问题，
// 因为 这里具体解析处理bean标签的解析器,processBeanDefinition方法分析
/**
*解析bean definition然后注册
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//将bean中的信息提取出来，封装到一个BeanDefinitionHolder对象中
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//注册最后的装饰实例(封装完成的BeanDefinition)
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
//发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
/**
*解析bean标签中的信息，然后将信息封装进BeanDefinitionHolder对象中
*/
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//获取id的属性值
String id = ele.getAttribute(ID_ATTRIBUTE);
//获取name的属性值
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List aliases = new ArrayList();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isDebugEnabled()) {
logger.debug("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) {
beanName = BeanDefinitionReaderUtils.generateBeanName(
beanDefinition, this.readerContext.getRegistry(), true);
}
else {
beanName = this.readerContext.generateBeanName(beanDefinition);
// Register an alias for the plain bean class name, if still possible,
// if the generator returned the class name plus a suffix.
// This is expected for Spring 1.2/2.0 backwards compatibility.
String beanClassName = beanDefinition.getBeanClassName();
if (beanClassName != null &&
beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
aliases.add(beanClassName);
}
}
if (logger.isDebugEnabled()) {
logger.debug("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
/**
* 创建beanDefinition实例
*/
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
try {
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析
parseMetaElements(ele, bd);
// 解析 bean标签解析成功之后，进行注册
/**
*
* 鉴于bean factory来注册bean definition
*/
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// 注册bean使用最原始的名称
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// 如果有别名就使用别名来注册
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
//注册别名
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;
//查看beanName名称是否被注册
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
//如果beanName名称已经被注册过，并且没有bean覆盖标识则抛出异常
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 (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
}
else {
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
this.frozenBeanDefinitionNames = null;
}
//所有的bean信息都会放进该map中，这个map用来保存所有的beanDefinition信息
this.beanDefinitionMap.put(beanName, beanDefinition);
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
==总结==:到了当前的阶段，xml中的Bean信息已经被解析完毕，Bean容器已经被初始化。Bean标签中的相关配置也装换成相应的BeanDefinition对象，已经注册到BeanDefinition中心，注册事件也已经发布成功。