接上一篇文章
对于容器来说,refresh是一个很重要的方法.让我们看一下它的实现.
可以在AbstractApplicationContext类(该类是FileSystemXmlApplicationContext的基类)中找到这个方法,它详细地描述了整个ApplicationContext的初始化过程,比如BeanFactory的更新,messagesource和postprocessor的注册等等,这个执行过程为ioc容器bean的生命周期管理提供了条件.
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//这是在子类中启动refreshBeanFactory()的地方
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();
}
}
}
我们进入到AbstractRefreshableApplicationContext的refreshBeanFactory方法中,这个方法创建了BeanFactory.在创建ioc容器前,如果已经有容器存在,先要把已有的容器销毁和关闭,保证在refresh之后使用的新建立起来的ioc容器
//AbstractRefreshableApplicationContext的refreshBeanFactory方法
@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);
}
}
这里调用的loadBeanDefinitions实际上是一个抽象方法,那么实际上的载入过程又在哪里呢?
我们看看loadBeanDefinition在AbstractRefreshableApplicationContext的子类AbstractXmlApplicationContext中的实现,在这个loadBeanDefinition中,初始化了读取器XmlBeanDefinitionReader,然后再把这个读取器在ioc容器中设置好,最后启动读取器来完成BeanDefinition在ioc容器中的载入.
//AbstractXmlApplicationContext中的loadBeanDefinition
public abstract class AbstractXmlApplicationContext extends AbstractRefreshableConfigApplicationContext {
private boolean validating = true;
/**
* Create a new AbstractXmlApplicationContext with no parent.
*/
public AbstractXmlApplicationContext() {
}
/**
* Create a new AbstractXmlApplicationContext with the given parent context.
* @param parent the parent context
*/
public AbstractXmlApplicationContext(ApplicationContext parent) {
super(parent);
}
/**
* Set whether to use XML validation. Default is {@code true}.
*/
public void setValidating(boolean validating) {
this.validating = validating;
}
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
//这里是实现loadBeanDefinitions的地方
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefi nitionReader(beanFactory);
//创建XmlBeanDefinitionReader,并通过回调设置到BeanFactory中去
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
//这里设置XmlBeanDefinitionReader为XmlBeanDefinitionReader配置ResourceLoader,因为DefaultResourceLoader是父类,
//所以this可以直接被使用
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.
//这里是启动bean信息载入的过程
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
/**
* Initialize the bean definition reader used for loading the bean
* definitions of this context. Default implementation is empty.
* <p>Can be overridden in subclasses, e.g. for turning off XML validation
* or using a different XmlBeanDefinitionParser implementation.
* @param reader the bean definition reader used by this context
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass
*/
protected void initBeanDefinitionReader(XmlBeanDefinitionReader reader) {
reader.setValidating(this.validating);
}
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
* method; hence this method is just supposed to load and/or register bean definitions.
* @param reader the XmlBeanDefinitionReader to use
* @throws BeansException in case of bean registration errors
* @throws IOException if the required XML document isn't found
* @see #refreshBeanFactory
* @see #getConfigLocations
* @see #getResources
* @see #getResourcePatternResolver
*/
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);
}
}
/**
* Return an array of Resource objects, referring to the XML bean definition
* files that this context should be built with.
* <p>The default implementation returns {@code null}. Subclasses can override
* this to provide pre-built Resource objects rather than location Strings.
* @return an array of Resource objects, or {@code null} if none
* @see #getConfigLocations()
*/
protected Resource[] getConfigResources() {
return null;
}
接着就是loadBeanDefinitions调用的地方,首先得到BeanDefinition信息的Resource定位,然后直接调用XmlBeanDefinitionReader读取,具体的载入过程是委托给BeanDefinitionReader完成的,因为这里的BeanDefinition是通过xml文件定义的,所以这里使用XmlBeanDefinitionReader来载入BeanDefinition到ioc容器当中。
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
* method; hence this method is just supposed to load and/or register bean definitions.
* @param reader the XmlBeanDefinitionReader to use
* @throws BeansException in case of bean registration errors
* @throws IOException if the required XML document isn't found
* @see #refreshBeanFactory
* @see #getConfigLocations
* @see #getResources
* @see #getResourcePatternResolver
*/
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);
}
}
/**
* Return an array of Resource objects, referring to the XML bean definition
* files that this context should be built with.
* <p>The default implementation returns {@code null}. Subclasses can override
* this to provide pre-built Resource objects rather than location Strings.
* @return an array of Resource objects, or {@code null} if none
* @see #getConfigLocations()
*/
protected Resource[] getConfigResources() {
return null;
}
通过以上原理的分析,我们可以看到,在初始化FileSystemXmlApplicationContext的过程中,通过调用ioc容器的refresh来启动整个BeanDefinition的载入过程的,这些初始化是通过定义的XmlBeanDefinitionReader来完成的.同时,我们也知道实际使用的容器是DefaultListableBeanFactory,具体的Resource载入在XmlBeanDefinitionReader读入BeanDefinition时实现。
因为spring可以对应不同形式的BeanDefinition,由于这里使用的是xml方式的定义,就需要使用XmlBeanDefinitionReader,如果使用了其他方式定义BeanDefinition方式,就需要使用其他种类的BeanDefinitionReade来完成数据的载入操作.
从XmlBeanDefinitionReader的实现中可以看到,是在reader.loadBeanDefinition中开始进行BeanDefinition的载入的，而这个时候XmlBeanDefinitionReader的父类AbstractBeanDefinitionReader已经为BeanDefinition的载入做好了准备
//AbstractBeanDefinitionReader载入BeanDefinition
@Override
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int counter = 0;
for (Resource resource : resources) {
counter += loadBeanDefinitions(resource);
}
return counter;
}
这里调用的是 loadBeanDefinitions(Resource res)方法,然而这个方法在AbstractBeanDefinitionReader类里面是没有实现的,他是一个接口方法,具体的实现在XmlBeanDefinitionReader中,在读取器中,需得到代表xml文件的Resource,因为一个Resource对象封装了对xml文件的IO操作,所以读取器可以在打开io流后得到xml文件对象,有了这个Document对象以后,可以按照Spring的Bean定义规则来对这个xml文档树进行解析了,这个解析是交给BeanDefinitionParserDelegate来完成的
//这里是调用的入口
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
/**
* Load bean definitions from the specified XML file.
* @param encodedResource the resource descriptor for the XML file,
* allowing to specify an encoding to use for parsing the file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
*/
//这里是载入xml形式的BeanDefinition的地方
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!");
}
//这里得到xml文件,并得到io的InputSource准备进行读取
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();
}
}
}
//具体的读取过程可以再doLoadBeanDefinitions方法中找到
//这是从特定的xml文件中实际载入BeanDefinition的地方
/**
* Actually load bean definitions from the specified XML file.
* @param inputSource the SAX InputSource to read from
* @param resource the resource descriptor for the XML file
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of loading or parsing errors
* @see #doLoadDocument
* @see #registerBeanDefinitions
*/
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//这里取得xml文件的Document对象,这个解析过程是由documentLoader完成的
Document doc = doLoadDocument(inputSource, resource);
//这里启动的是对BeanDefinition解析的详细过程,这个解析会用到spring的bean配置规则,是我们下面需要详细关注的地方.
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);
}
}
protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
//这个documentLoader对象是在定义documentLoader的地方创建的
return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
getValidationModeForResource(resource), isNamespaceAware());
}
//registerBeanDefinitions的代码实现
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();
int countBefore = getRegistry().getBeanDefinitionCount();
//具体的解析过程在这个registerBeanDefinition中完成
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
BeanDefinition的载入包括两部分,首先是通过调用xml解析器得到document对象,但这些document对象并没有按照spring的规则进行解析。在完成通用的xml解析之后,才是按照spring的bean规则进行解析的地方,按照spring的bean规则进行解析的过程是在documentReader
中实现的.这里使用的documentReader是默认设置好的DefaultBeanDefinitionDocumentReader.这个DefaultBeanDefinitionDocumentReader的创建是在以下的方法里完成的,然后再完成BeanDefinition的处理,处理的结果由BeanDefinitionHolder对象来持有.这个BeanDefinitionHolder对象除了持有BeanDefinition对象外,还持有了其他与BeanDefinition的使用相关的信息,比如Bean的名字、别名集合等.这个BeanDefinitionHolder的生成是通过对Document文档树的内容进行解析来完成的,可以看到这个解析过程是由BeanDefinitionParserDelegate来实现的,实现原理的代码如下
//在XmlBeanDefinitionReader中
/**
* Create the {@link BeanDefinitionDocumentReader} to use for actually
* reading bean definitions from an XML document.
* <p>The default implementation instantiates the specified "documentReaderClass".
* @see #setDocumentReaderClass
*/
protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
return BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
}
//这样得到了documentReader之后,为具体的SpringBean解析过程准备好了数据
//在DefaultBeanDefinitionDocumentReader中
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
//这里是向ioc容器注册解析得到的BeanDefinition的地方
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
//向容器注册完后,发送消息
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
具体的Spring BeanDefinition的解析是在BeanDefinitionParserDelegate中完成的,在这里我们可以看那些熟悉的BeanDefinition的元素属性进行处理,比如id,name,aliase等属性元素,把这些元素的值从xml文件相应的元素属性读取出来后,再被设置到BeanDefinitionHolder中去。对于其它属性的解析,比如各种Bean的属性配置,通过一个较为复杂的解析过程,这个解析过程是由parseBeanDefinitionElement来完成的,解析完成后,会把
解析结果放到BeanDefinition对象中并设置到BeanDefinitionHolder中去
//BeanDefinitionParserDelegate对bean元素的处理
/**
* Parses the supplied {@code <bean>} element. May return {@code null}
* if there were errors during parse. Errors are reported to the
* {@link org.springframework.beans.factory.parsing.ProblemReporter}.
*/
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//这里取得在<bean>元素中定义的id，name和aliases属性的值
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
List<String> aliases = new ArrayList<String>();
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);
}
//这个方法会引发对bean元素的详细解析
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;
}
上面就是Bean元素进行解析的过程,也就是BeanDefinition依据xml的<bean>定义被创建的过程,这个BeanDefinition可以看做是对bean定义的抽象,这个对象封装的数据大多是与<bean>定义相关的
BeanDefinition的数据定义.png
//对BeanDefinition定义元素的处理
/**
* Parse the bean definition itself, without regard to name or aliases. May return
* {@code null} if problems occurred during the parsing of the bean definition.
*/
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
//这里只读取定义<bean>中的class名字,然后载入到BeanDefinition中去,只是做个记录,并不涉及对象的实例化过程,对象的实例化实际上是在依赖注入时完成的
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);
}
//这里生成BeanDefinition对象,为Bean定义信息的载入做准备
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//这里对当前的bean元素进行属性解析,并设置description的信息
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//从名字可以看出,这里是对各种<bean>元素的信息进行解析的地方
parseMetaElements(ele, bd);
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解析<bean>的构造函数设置
parseConstructorArgElements(ele, bd);
//解析<bean>的property设置
parsePropertyElements(ele, bd);
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
//下面这些异常时我们在配置bean时出现问题时经常可以看到的
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
return null;
}
上面是具体生成BeanDefinition的地方,在这里,我们举一个对property进行解析的例子来完成对整个BeanDefinition载入过程的分析,还是在类BeanDefinitionParserDelegate的代码中,它对BeanDefinition中的定义一层一层地进行解析,比如从属性元素集合到具体的没一个属性元素,根据解析结果,这些属性元素的值的处理会封装成PropertyValue对象并设置到BeanDefinition对象中去
//对BeanDefinition中Property元素集合的处理
/**
* Parse property sub-elements of the given bean element.
*/
//这里对指定bean元素的property子元素集合进行解析
public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
NodeList nl = beanEle.getChildNodes();
//遍历所有的bean元素下定义的property元素
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
//在判断是property元素后对该property元素进行解析的过程
parsePropertyElement((Element) node, bd);
}
}
}
/**
* Parse a property element.
*/
public void parsePropertyElement(Element ele, BeanDefinition bd) {
//这里取得property的名字
String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
if (!StringUtils.hasLength(propertyName)) {
error("Tag 'property' must have a 'name' attribute", ele);
return;
}
this.parseState.push(new PropertyEntry(propertyName));
try {
//如果同一个bean中已经有同名的property的存在,则不进行解析,直接返回,起作用的只是第一个
if (bd.getPropertyValues().contains(propertyName)) {
error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
return;
}
//这里是解析property值的地方,返回的对象对应对bean定义的property属性
//设置的解析结果,这个解析结果会封装到PropertyValue中去,然后设置到BeanDefinitionHolder中去
Object val = parsePropertyValue(ele, bd, propertyName);
PropertyValue pv = new PropertyValue(propertyName, val);
parseMetaElements(ele, pv);
pv.setSource(extractSource(ele));
bd.getPropertyValues().addPropertyValue(pv);
}
finally {
this.parseState.pop();
}
}
/**
* Get the value of a property element. May be a list etc.
* Also used for constructor arguments, "propertyName" being null in this case.
*/
//这里取得property元素的值,可能是list或者其他
public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
String elementName = (propertyName != null) ?
"<property> element for property '" + propertyName + "'" :
"<constructor-arg> element";
// Should only have one child element: ref, value, list, etc.
NodeList nl = ele.getChildNodes();
Element subElement = null;
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&
!nodeNameEquals(node, META_ELEMENT)) {
// Child element is what we're looking for.
if (subElement != null) {
error(elementName + " must not contain more than one sub-element", ele);
}
else {
subElement = (Element) node;
}
}
}
//这里判断property的属性,是ref还是value,不允许同时是ref和value
boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);
boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);
if ((hasRefAttribute && hasValueAttribute) ||
((hasRefAttribute || hasValueAttribute) && subElement != null)) {
error(elementName +
" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
}
//如果是ref,创建一个ref的数据对象RuntimeBeanReference,这个对象封装了ref的信息
if (hasRefAttribute) {
String refName = ele.getAttribute(REF_ATTRIBUTE);
if (!StringUtils.hasText(refName)) {
error(elementName + " contains empty 'ref' attribute", ele);
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName);
ref.setSource(extractSource(ele));
return ref;
}
//如果是value，创建一个TypedStringValue,这个对象封装了value的信息
else if (hasValueAttribute) {
TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));
valueHolder.setSource(extractSource(ele));
return valueHolder;
}
//如果还有子元素,触发对子元素的解析
else if (subElement != null) {
return parsePropertySubElement(subElement, bd);
}
else {
// Neither child element nor "ref" or "value" attribute found.
error(elementName + " must specify a ref or value", ele);
return null;
}
}
这里是对property子元素的解析过程,Array,List,Set,Map,Prop等各种元素都会在这里进行解析,生成对应的数据对象,比如ManagedList,ManagedArray,ManagedSet等,这些Managed类是Spring对具体的BeanDefinition的数据封装.
下面,以对Property的元素进行的解析过程为例,来看一下具体的解析过程
/**
* Parse a value, ref or collection sub-element of a property or
* constructor-arg element.
* @param ele subelement of property element; we don't know which yet
* @param defaultValueType the default type (class name) for any
* {@code <value>} tag that might be created
*/
public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
if (!isDefaultNamespace(ele)) {
return parseNestedCustomElement(ele, bd);
}
else if (nodeNameEquals(ele, BEAN_ELEMENT)) {
BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);
if (nestedBd != null) {
nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
}
return nestedBd;
}
else if (nodeNameEquals(ele, REF_ELEMENT)) {
// A generic reference to any name of any bean.
String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);
boolean toParent = false;
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in the same XML file.
refName = ele.getAttribute(LOCAL_REF_ATTRIBUTE);
if (!StringUtils.hasLength(refName)) {
// A reference to the id of another bean in a parent context.
refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);
toParent = true;
if (!StringUtils.hasLength(refName)) {
error("'bean', 'local' or 'parent' is required for <ref> element", ele);
return null;
}
}
}
if (!StringUtils.hasText(refName)) {
error("<ref> element contains empty target attribute", ele);
return null;
}
RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
ref.setSource(extractSource(ele));
return ref;
}
else if (nodeNameEquals(ele, IDREF_ELEMENT)) {
return parseIdRefElement(ele);
}
else if (nodeNameEquals(ele, VALUE_ELEMENT)) {
return parseValueElement(ele, defaultValueType);
}
else if (nodeNameEquals(ele, NULL_ELEMENT)) {
// It's a distinguished null value. Let's wrap it in a TypedStringValue
// object in order to preserve the source location.
TypedStringValue nullHolder = new TypedStringValue(null);
nullHolder.setSource(extractSource(ele));
return nullHolder;
}
else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {
return parseArrayElement(ele, bd);
}
else if (nodeNameEquals(ele, LIST_ELEMENT)) {
return parseListElement(ele, bd);
}
else if (nodeNameEquals(ele, SET_ELEMENT)) {
return parseSetElement(ele, bd);
}
else if (nodeNameEquals(ele, MAP_ELEMENT)) {
return parseMapElement(ele, bd);
}
else if (nodeNameEquals(ele, PROPS_ELEMENT)) {
return parsePropsElement(ele);
}
else {
error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
return null;
}
}
再让我们看看类似于List这样的属性配置是怎样被解析的,依然在BeanDefinitionParserDelegate中,返回的是一个List对象，这个List是Spring定义的ManagedList,作为封装这个List这个配置定义的数据封装.
/**
* Parse a list element.
*/
public List<Object> parseListElement(Element collectionEle, BeanDefinition bd) {
String defaultElementType = collectionEle.getAttribute(VALUE_TYPE_ATTRIBUTE);
NodeList nl = collectionEle.getChildNodes();
ManagedList<Object> target = new ManagedList<Object>(nl.getLength());
target.setSource(extractSource(collectionEle));
target.setElementTypeName(defaultElementType);
target.setMergeEnabled(parseMergeAttribute(collectionEle));
//具体的list解析过程
parseCollectionElements(nl, target, bd, defaultElementType);
return target;
}
protected void parseCollectionElements(
NodeList elementNodes, Collection<Object> target, BeanDefinition bd, String defaultElementType) {
//遍历所有的元素节点,判断其类型是否为Element
for (int i = 0; i < elementNodes.getLength(); i++) {
Node node = elementNodes.item(i);
if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT)) {
//加入到target中,target是一个ManageList,同时触发对下一个子元素的解析.这是一个递归调用
target.add(parsePropertySubElement((Element) node, bd, defaultElementType));
}
}
}
经过这样逐层解析,我们在xml文件中定义的BeanDefinition就被整个载入到了ioc容器当中,并在容器中建立了数据映射,在ioc容器中建立了对应的数据结构,或者说可以看成是POJO对象在IOC容器中的映象，这些数据结构可以以AbstractBeanDefinition为入口,让IOC容器执行索引，查询和操作。
现在,在IOC容器中还只是一些静态的数据配置信息,这个时候的容器还没有完全起作用,要完全发挥容器的作用,还需要完成数据向容器中注册.
2.3.3 BeanDefinition在ioc容器中的注册
我们已经分析过BeanDefinition在ioc容器中的载入和解析的过程,这些动作完成以后,用户定义的BeanDefinition信息已经在ioc容器内建立起了自己的数据结构以及相应的数据表示,但此时的这些数据还不能让ioc容器直接使用,需要在ioc容器中对这些BeanDefinition数据进行注册。这个注册为ioc容器提供了更友好的使用方式,在DefaultListableBeanFActory中,是通过一个HashMap来持有载入的BeanDefinition的,这个HashMap的定义在DefaultListableBeanFactory可以看到,如下图所示
/** Map of bean definition objects, keyed by bean name */
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(256);
将解析到的BeanDefinition向ioc容器中的beanDefinitionMap注册的过程是在载入BeanDefinition完成后进行的,注册的调用过程如下
registerBeanDefinition的调用过程.png
在DefaultListableBeanFactory中实现了BeanDefinitionRegistry 接口,这个接口的实现完成BeanDefinition的注册.这个注册过程并不复杂,就是把解析到的BeanDefinition设置到HashMap中去,需要注意的地方是遇到同名的BeanDefinition的情况,进行处理的时候需要依据allowBeanDefinitionOverriding的配置来完成
具体的实现代码如下
//---------------------------------------------------------------------
// Implementation of BeanDefinitionRegistry interface
//---------------------------------------------------------------------
@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;
//这里检查是不是有相同名字的 BeanDefinition已经在容器中注册了,如果有相同名字的,但又不允许覆盖,抛出异常
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 + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
//这里需要synchronized来保证数据的一致性
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<String>(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);
}
}
小结:
完成了BeanDefinition的注册,就完成了ioc容器的初始化过程,此时,在我们使用的ioc容器DefaultListableBeanFactory中已经建立了整个Bean的配置信息,而且这些BeanDefinition已经可以被容器使用了,它们都可以在beanDefinitionMap里检索和使用,容器的作用就是对这些信息进行处理和维护。这些信息时容器建立依赖反转的基础。
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