Spring源码之XMLBeanFactory
本文是针对Srping的XMLBeanFactory来进行解析xml并将解析后的信息使用GenericBeanDefinition作为载体进行注册,xmlBeanFactory已经在Spring 3.1中被标记为不建议使用，但是我们分析源码不影响，因为源码并未改变，并ApplicationContext依旧使用XmlBeanDefinitionReader和DefaultListableBeanFactory进行xml的解析和注册工作，本篇博客是跟源码一步步看spring怎么实现bean的注册，源码为spring5.X,源码已经在每一行上加了注释，方便读者学习。
GitHub:https://github.com/lantaoGitHub/spring-framework.git
- 首先我们从XMLBeanFactory入手,直接上代码：
package org.springframework.lantao;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
public class XmlBeanFactoryTest {
public static void main(String[] args) {
// 资源加载
ClassPathResource classPathResource = new ClassPathResource("spring-bean.xml");
// XmlBeanFactory 加载资源并解析注册bean
BeanFactory beanFactory = new XmlBeanFactory(classPathResource);
// BeanFactory.getBean();
UserBean userBean = (UserBean) beanFactory.getBean("userBean");
System.out.println(userBean.getName());
}
}
- XmlBeanFactory解析Xml是使用了XmlBeanDefinitionReader.loadBeanDefinition()方法,源码如下：
@Deprecated
@SuppressWarnings({"serial", "all"})
public class XmlBeanFactory extends DefaultListableBeanFactory {
private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);
/**
* Create a new XmlBeanFactory with the given resource,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource) throws BeansException {
//调用构造方法 79行
this(resource, null);
}
/**
* Create a new XmlBeanFactory with the given input stream,
* which must be parsable using DOM.
* @param resource the XML resource to load bean definitions from
* @param parentBeanFactory parent bean factory
* @throws BeansException in case of loading or parsing errors
*/
public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
//ignoreDependencyInterface 忽略自动装配
//主要功能就是当有忽略的接口类，自动装配会忽略这部分类的初始化装配，因为某种情况下，此时的接口实现类不能初始化，列如BeanNameAware,要想装配这个接口的实现对象，可以实现这个接口。
super(parentBeanFactory);
//这段代码是真正的资源加载
this.reader.loadBeanDefinitions(resource);
}
}- 我们直接看loadBeanDefinition方法，源码：
/**
* Load bean definitions from the specified XML file.
* @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
*/
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
// 对EncodedResource进行封装，设置String encoding, Charset charset
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
*/
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
//encodedResource 不可以为空
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isTraceEnabled()) {
logger.trace("Loading XML bean definitions from " + encodedResource);
}
// 通过属性来记录已经加载的资源
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 {
// 从encodedResource已经封装的Resource获取InputStream
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
//InputSource 并不是spring的，而是 org.xml.sax
InputSource inputSource = new InputSource(inputStream);
//如果encodedResource 中的 Encoding 不是 null 则同步设置 InputSource的 Encoding
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//加载bean的Definitions 将xml中的信息加载到Definition中，并且在内存中注册的也是key+definitions
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();
}
}
} 上述源码可能看着比较长,但实际上这里并不是真正解析的地方，在这里做了如下：
1:从encodedResource已经封装的Resource获取InputStream；
2:如果encodedResource 中的 Encoding 不是 null 则同步设置 InputSource的 Encoding；
3:将解析动作委托给doLoadBeanDefinitions实现；
- 接下来我们继续看doLoadBeanDefinitions方法内容：
/**
* 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 {
//加载 Document
Document doc = doLoadDocument(inputSource, resource);
//注册 bean
int count = registerBeanDefinitions(doc, resource);
if (logger.isDebugEnabled()) {
logger.debug("Loaded " + count + " bean definitions from " + resource);
}
return count;
}
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);
}
}当我们看着这个方法的时候，依旧不是真正的解析或注册的方法，在这里只是做了Document的加载，并将后续工作委托给了registerBeanDefinitions,registerBeanDefinitions方法的返回时注册Bean的个数；
- 我们继续看registerBeanDefinitions的源码：
/**
* Register the bean definitions contained in the given DOM document.
* Called by {@code loadBeanDefinitions}.
* Creates a new instance of the parser class and invokes
* {@code registerBeanDefinitions} on it.
* @param doc the DOM document
* @param resource the resource descriptor (for context information)
* @return the number of bean definitions found
* @throws BeanDefinitionStoreException in case of parsing errors
* @see #loadBeanDefinitions
* @see #setDocumentReaderClass
* @see BeanDefinitionDocumentReader#registerBeanDefinitions
*/
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//实例化 BeanDefinitionDocumentReader
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//获取之前的beanDefinition加载个数
int countBefore = getRegistry().getBeanDefinitionCount();
//加载xml及注册bean
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
//记录本次加载个数
return getRegistry().getBeanDefinitionCount() - countBefore;
}
在registerBeanDefinitions方法具体实现：
1：通过BeanUtils.instantiateClass(this.documentReaderClass)的方法实例化BeanDefinitionDocumentReader；
2：通过DefaultListAbleBeanFactory中的beanDefinitionMap.size()获取之前注册bean的个数，（beanDefinitionMap是存储最终的xml解析后信息的载体，xml解析后信息是由GenericBeanDefinition进行存储，beanDefinitionMap的存储格式是key:String value:GenericBeanDefinition）
3:将解析xml和注册的工作委托给BeanDefinitionDocumentReader的registerBeanDefinitions方法；
4：记录本次加载个数并返回；
- 继续看BeanDefinitionDocumentReader的registerBeanDefinitions方法：
/**
* This implementation parses bean definitions according to the "spring-beans" XSD
* (or DTD, historically).
* Opens a DOM Document; then initializes the default settings
* specified at the {@code
- registerBeanDefinitions并没有做什么，我们继续看doRegisterBeanDefinitions方法：
/**
* Register each bean definition within the given root {@code elements will cause recursion in this method. In
// order to propagate and preserve default-* attributes correctly,
// keep track of the current (parent) delegate, which may be null. Create
// the new (child) delegate with a reference to the parent for fallback purposes,
// then ultimately reset this.delegate back to its original (parent) reference.
// this behavior emulates a stack of delegates without actually necessitating one.
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = createDelegate(getReaderContext(), root, parent);
//验证xml namespace, BeanDefinitionParserDelegate.BEANS_NAMESPACE_URI
if (this.delegate.isDefaultNamespace(root)) {
//获取Attribute
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// We cannot use Profiles.of(...) since profile expressions are not supported
// in XML config. See SPR-12458 for details.
if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
"] not matching: " + getReaderContext().getResource());
}
return;
}
}
}
//解析前处理， 内容null 留个子类实现
preProcessXml(root);
//解析
parseBeanDefinitions(root, this.delegate);
//解析后处理， 内容null 留个子类实现
postProcessXml(root);
this.delegate = parent;
} 在doRegisterBeanDefinitions烦那个发中验证xml的namespace,最重要的方法是parseBeanDefinitions，parseBeanDefinitions方法进行了解析操作；
- parseBeanDefinitions方法的源码：
/**
* Parse the elements at the root level in the document:
* "import", "alias", "bean".
* @param root the DOM root element of the document
*/
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//验证xml namespace, BeanDefinitionParserDelegate.BEANS_NAMESPACE_URI
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;
if (delegate.isDefaultNamespace(ele)) {
//对默认标签处理
parseDefaultElement(ele, delegate);
}
else {
//对自定义标签处理
delegate.parseCustomElement(ele);
}
}
}
}
else {
//对自定义标签处理
delegate.parseCustomElement(root);
}
}parseBeanDefinitions方法中已经开始对标签进行解析，区分默认标签和自定义标签，我们本次只对默认标签的源码进行解析，自定义标签自行DeBug，
- parseDefaultElement方法的源码：
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
//解析import标签
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
//解析alias标签并注册
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
//解析bean标签并注册
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
//解析beans标签
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}到这里我们可以看到，spring对import/bean/alias/beans的解析过程，对于beans的解析无法就是解析beans中的bean标签，spring直接又重新调用了doRegisterBeanDefinitions方法，我们接下来进行对bean标签的解析；
- processBeanDefinition方法：
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//委托BeanDefinitionParserDelegate的parseBeanDefinitionElement方法进行元素解析并返回
//BeanDefinitionHolder实例，BeanDefinitionHolder已经包含了配置文件中的各种属性
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
//当BeanDefinitionHolder返回不null的情况，弱存在默认标签下的子标签再有自定义的属性，还需要再次解析
if (bdHolder != null) {
//解析默认标签中的自定义标签
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
// 进行实例注册注册操作是BeanDefinitionReaderUtisl.registerBeanDefinition进行处理
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));
}
}在processBeanDefinition方法中，spring做了两件事情：
1：委托BeanDefinitionParserDelegate的parseBeanDefinitionElement方法进行元素解析并返回BeanDefinitionHolder实例，BeanDefinitionHolder已经包含了配置文件中的各种属性
2：通过上获得的BeanDefinitionHolder进行bean的注册操作，通BeanDefinitionReaderUtils.registerBeanDefinition方法；
- 通过delegate.parseBeanDefinitionElement方法进行xml解析：
/**
* Parses the supplied {@code } element. May return {@code null}
* if there were errors during parse. Errors are reported to the
* {@link org.springframework.beans.factory.parsing.ProblemReporter}.
*/
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//解析id属性
String id = ele.getAttribute(ID_ATTRIBUTE);
//解析name属性
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//分割name属性
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.isTraceEnabled()) {
logger.trace("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
//将信息封装到 beanDefinition中
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
//beanname不存在则使用默认规则创建
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.isTraceEnabled()) {
logger.trace("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;
} 在parseBeanDefinitionElement方法中做了三件事：
1：解析id/name；
2：检查name的唯一性；
3：将信息封装到 beanDefinition中，接下来直接看parseBeanDefinitionElement方法；
- parseBeanDefinitionElement源码：
/**
* 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.
*/
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
//解析classname属性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//解析parent属性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
//创建用于承载属性的AbstractBeanDefinition类型的
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//解析bean的各种属性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//提取description
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//解析meta （元数据）
parseMetaElements(ele, bd);
//解析Lookup-method 书中53页有使用方法
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//解析replaced-method 书中55页有使用方法
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//构造函数 参数
//解析constructor-arg 书中replaced-method后边
parseConstructorArgElements(ele, bd);
//解析Property 书中replaced-method后边
parsePropertyElements(ele, bd);
//解析Qualifier 书中Property后边
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
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;
}通过上述代码我们可以看到这里首先是实例化了一个AbstractBeanDefinition来承载各种xml属性，接下来通过parseBeanDefinitionAttributes方法解析了xml中的各种你属性值，然后在解析lookUp-method(方法注入)，replaced-method(替换方法或方法返回值)，构造函数参数constructor-arg，property属性，Qualifier属性等；上述方法的源码就不一一展示了，无非都是通过Element进行解析；
- 接下来看真正注册的代码 BeanDefinitionReaderUtils.registerBeanDefinition
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
//beanName不可为空
Assert.hasText(beanName, "Bean name must not be empty");
//beanDefinition不可为空
Assert.notNull(beanDefinition, "BeanDefinition must not be null");
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
//校验 MethodOverrides，MethodOverrides在解析并组装beanDefinition时有提到
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//beanDefinitionMap 存储实例的全局Map 使用ConcurrentHashMap 线程安全
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
//如果已经注册 处理内容
if (existingDefinition != null) {
//是否覆盖
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
//判断是否已经至少创建过一次 使用AbstractBeanFactory.alreadyCreated来判断
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// 仍处于启动注册阶段
// 注册 beanDefinitionMap 新实例 beanName + beanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
// 增加beanDefinitionNames
this.beanDefinitionNames.add(beanName);
// 清除缓存
this.manualSingletonNames.remove(beanName);
}
// 清除缓存
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
} 上述代码中首先验证了beanName和BeannDefinition不可为空,然后继续校验了MethodOverridesMethodOverrides在解析并组装beanDefinition时lookup-method和recpse-method的源码中有提到，继续判断beanDefinitionMap是否存在该bean，如果bean已经存在，通过allowBeanDefinitionOverriding属性判断是否可覆盖，反之则抛出异常；如果不存在则需要判断本次是否是第一次注册bean，如果是则初始化beanDefinitionMap后进行put操作，反之直接put beanDefinitionMap完成注册；
至此我们已经看完了整个XmlBeanFactory的xml解析和注册的源码部分，相信看本篇文章无法真正理解，还需要读者下载源码使用debug运行，再结合本篇文章的注释，相信会很容易理解，码字不易，转发请注明出处：https://blog.csdn.net/qq_30257149/article/details/87972291
欢迎加入作者的微信公众号：