spring： xml到BeanDefinition的解析
XmlBeanDefinitionRead简称xmlRead ，其功能就是把xml文件转换为bean的描述类BeanDefinition。
转换过程：
1：找到对应的xml文件。
2：转换为docment对象。
3：docment对象翻译成BeanDefinition。
xmlRead的继承关系图
Read的接口方法
Read的实现类有：
所以xml配置bean只是spring其中的一种方法。
XmlRead的构造方法：
/**
* Create new XmlBeanDefinitionReader for the given bean factory.
* @param registry the BeanFactory to load bean definitions into,
* in the form of a BeanDefinitionRegistry
*/
public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
super(registry);
}
需要传一个BeanDefinitionRegistry，spring中的实现类有
DefaultListableBeanFactory是factory最基础的实现类，同时也是BeanDefinitionRegistry的实现类。
下面创建一个简单的spring工厂。
public static void main(String[] args) {
// 一个简单的spring工厂
//1.定位资源
Resource resource = new ClassPathResource("app_1.xml");
//2.工厂生成
DefaultListableBeanFactory defaultListableBeanFactory = new DefaultListableBeanFactory();
//3.创建Read
BeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(defaultListableBeanFactory);
//4.xml文件中的bean解析成beanDefinition
beanDefinitionReader.loadBeanDefinitions(resource);
//5.实例化单例的bean
defaultListableBeanFactory.preInstantiateSingletons();
}
app_1.xml
load关键过程：
XmlBeanDefinitionReader：public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
。。。。。。。。
//资源转为流
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
。。。。。。。。。
}
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {
try {
//xml解析为doc
Document doc = doLoadDocument(inputSource, resource);
return registerBeanDefinitions(doc, resource);
}public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//创建一个docRead --->DefaultBeanDefinitionDocumentReader 由它来转换doc----》beandifition
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}DefaultBeanDefinitionDocumentReader：
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
this.readerContext = readerContext;
logger.debug("Loading bean definitions");
Element root = doc.getDocumentElement();
doRegisterBeanDefinitions(root);
}protected void doRegisterBeanDefinitions(Element root) {
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
//判断命名空间是不是http://www.springframework.org/schema/beans
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE); //profile
//处理 profile
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);
//解析doc
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判断是不是http://www.springframework.org/schema/beans
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes();
for (int i = 0; i < nl.getLength(); i++) {
Node node = nl.item(i);
if (node instanceof Element) {
Element ele = (Element) node;
//spring 原生的命名空间
if (delegate.isDefaultNamespace(ele)) {
//解析某个元素
parseDefaultElement(ele, delegate);
}
//解析哪些自定义的标签 比如 context，mvc标签就是在这里处理的。
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
//处理自定义的命名空间
delegate.parseCustomElement(root);
}
}
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
import 标签的处理
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
alias 标签的处理
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
bean标签的处理
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
beans的处理
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
//关键步骤：doc的exelment ----------》beandefinition
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//在这里解析
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}BeanDefinitionParserDelegate：public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE);
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) {
//id name 都配置，beanName 为id
//如果id name 都不配置则自动生成：类似这种 com.spring.bean.BeanA#0，当然不一定就是这样，可以自己去研究一下。
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;
}
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
parseMetaElements(ele, bd);
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
parseConstructorArgElements(ele, bd); 构造参数
parsePropertyElements(ele, bd); //property解析
parseQualifierElements(ele, bd); //Qualifier属性
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}到此为止 xml -----》doc-------------》 GenericBeanDefinition 的转换工作已近完成 这三和存储的内容都是一样的 只不过是不同的描述而已。Bean的生成，就是把GenericBeanDefinition 在转化成Bean。