Spring5.0源码学习系列之浅谈BeanFactory创建过程
系列文章目录
提示：Spring源码学习专栏链接
@TOC
博客前言介绍
提示：在上一章的学习中，我们简单了解了Spring IoC容器启动初始化的主流程，不过并没有详细解释，因为代码比较复杂，没有做长篇大论，所以本文接着学习BenFactory的创建过程，学习源码建议带着疑问去学，一点点跟，时间积累之后就可以串起来
提示：以下是本篇文章正文内容，下面案例可供参考
一、获取BeanFactory主流程
在前面的学习中，#refresh是IoC容器创建很关键的主线，在代码里，可以找到obtainFreshBeanFactory这个比较关键的方法，这个方法就是BeanFactory的创建过程方法，本文ClassPathXmlApplicationContext为准，进行源码的学习，上篇博客是以AnnotationApplicationContext为准进行简单的分析，本文继续比较详细的讲述
实验环境：
- SpringFramework版本
- Springframework5.0.x
- 开发环境
- JAR管理：gradle 4.9/ Maven3.+
- 开发IDE：IntelliJ IDEA 2018.2.5
- JDK：jdk1.8.0_31
- Git Server：Git fro window 2.8.3
- Git Client：SmartGit18.1.5（可选）
maven项目，需要加上pom配置：
5.0.9.RELEASE
org.springframework
spring-context
${springframework.version}
如果是gradle环境，可以直接在Spring框架project里新增一个module，具体可以参考教程：加上对应的配置
SpringBean.java：
package com.example.bean;
import org.springframework.beans.factory.InitializingBean;
/**
*
* SpringBean
*
*
*
* @author mazq
* 修改记录
* 修改后版本: 修改人： 修改日期: 2020/11/05 10:50 修改内容:
*
*/
public class SpringBean implements InitializingBean {
public SpringBean(){
System.out.println("SpringBean构造函数");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("SpringBean afterPropertiesSet");
}
}
applicationContext.xml：
测试类，使用ClassPathXmlApplicationContext
package com.example;
import com.example.bean.SpringBean;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
*
* TestController
*
*
*
* @author mazq
* 修改记录
* 修改后版本: 修改人： 修改日期: 2020/11/05 10:22 修改内容:
*
*/
public class TestApplication {
public static void testClassPathXmlApplicationContext() {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
SpringBean springBean = context.getBean(SpringBean.class);
System.out.println(springBean);
}
public static void main(String[] args) {
// 测试ClassPathXmlApplicationContext
testClassPathXmlApplicationContext();
}
}
在SpringBean 打断点，debug进行调试：找到#refresh方法
obtainFreshBeanFactory示例：
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
// 创建BeanFactory
refreshBeanFactory();
// 返回refreshBeanFactory方法创建好的BeanFactory
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
然后refreshBeanFactory是由哪个基类实现的？我们找来一张uml类图：
从图可以知道
ClassPathXmlApplicationContext通过
AbstractRefreshableApplicationContext实现
AbstractApplicationContext，所以
refreshBeanFactory是
AbstractRefreshableApplicationContext#refreshBeanFactory
ok，所以主体的路线，就可以熟悉，用uml时序图表示：
二、refreshBeanFactory创建过程
refreshBeanFactory方法是BeanFactory的创建过程，接着跟
org.springframework.context.support.AbstractRefreshableApplicationContext#refreshBeanFactory代码如下（示例）：
/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
// 先判断是否有BeanFactory
if (hasBeanFactory()) {
// destroy Beans
destroyBeans();
// 关闭BeanFactory
closeBeanFactory();
}
try {
// 实例化DefaultListableBeanFactory
DefaultListableBeanFactory beanFactory = createBeanFactory();
// 设置序列化id
beanFactory.setSerializationId(getId());
// 定义BeanFactory的一些属性（是否允许Bean覆盖，是否允许循环依赖）
customizeBeanFactory(beanFactory);
// 加载应用中的BeanDefinition
loadBeanDefinitions(beanFactory);
this.beanFactory = beanFactory;
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
{@link org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions}
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
// 给BeanFactory实例化一个XmlBeanDefinitionReader实例
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(this.getEnvironment());
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.
// 给子类提供初始化XmlBeanDefinitionReader的模板方法
initBeanDefinitionReader(beanDefinitionReader);
// 重点在这，继续跟
loadBeanDefinitions(beanDefinitionReader);
}
// org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.support.DefaultListableBeanFactory)
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
Resource[] configResources = getConfigResources();
if (configResources != null) {
// 继续跟
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
reader.loadBeanDefinitions(configLocations);
}
}
{@link org.springframework.beans.factory.support.AbstractBeanDefinitionReader#loadBeanDefinitions}
@Override
public int loadBeanDefinitions(Resource... resources) throws BeanDefinitionStoreException {
Assert.notNull(resources, "Resource array must not be null");
int counter = 0;
// 变量资源对象，加载BeanDefinition
for (Resource resource : resources) {
// 在这里，经过debug，调到XmlBeanDefinitionReader.loadBeanDefinitions(resource)
counter += loadBeanDefinitions(resource);
}
// 返回统计数量，表示总共有多少个BeanDefinition
return counter;
}
XmlBeanDefinitionReader类
{@link org.springframework.beans.factory.xml.XmlBeanDefinitionReader#loadBeanDefinitions}
@Override
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
return loadBeanDefinitions(new EncodedResource(resource));
}
// 省略...
/**
* 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 {
Assert.notNull(encodedResource, "EncodedResource must not be null");
if (logger.isInfoEnabled()) {
logger.info("Loading XML bean definitions from " + encodedResource);
}
// 用ThreadLocal存放资源对象，目的是保证线程安全
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 {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
// 核心，往下跟
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();
}
}
}
/**
* 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 {
// 读取xml信息，将xml信息保存在Document对象
Document doc = doLoadDocument(inputSource, resource);
// 封装BeanDefinitions并注册，继续解析Document对象，往下跟
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);
}
}
/**
* 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 {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
// 获取已有的BeanDefinition数量
int countBefore = getRegistry().getBeanDefinitionCount();
// 注册BeanDefinition，关注点：registerBeanDefinitions、createReaderContext
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
// 返回新注册的BeanDefinition统计数量
return getRegistry().getBeanDefinitionCount() - countBefore;
}
{@link org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#registerBeanDefinitions}
/**
* 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 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);
if (this.delegate.isDefaultNamespace(root)) {
// profile(环境校验)
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
// 不是当前profile的，跳过
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模板方法
preProcessXml(root);
// 重点是parseBeanDefinitions
parseBeanDefinitions(root, this.delegate);
// postProcessXml 同样是模板方法 过
postProcessXml(root);
this.delegate = parent;
}
/**
* 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) {
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)) {
// 解析default namespace下面的元素
parseDefaultElement(ele, delegate);
}
else {
// 解析自定义标签元素
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
// import元素处理
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
// alias元素处理
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
// bean元素处理
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
// 嵌套beans处理
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}
bean元素处理，本文挑beana元素的处理进行讲述：
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析Bean元素为BeanDefinition，再通过BeanDefinitionHolder封装成BeanDefinitionHolder对象
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
// 有自定义属性会进行相应的解析
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
// BeanDefinition的注册过程
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));
}
}
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