源码跟读，Spring是如何解析和加载xml中配置的beans
Spring版本基于：
1、配置启动Spring所需的监听器
web.xml中配置监听器
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>3
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<listener>
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<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
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</listener>
这是一个典型的 ServletContextListener，Servlet 容器（如 Tomcat 等）在启动时会找到 ContextLoaderListener 并执行其 contextInitialized(ServletContextEvent event) 方法。
ContextLoaderListener.java extends ContextLoader implements ServletContextListener
public void contextInitialized(ServletContextEvent event) {
this.contextLoader = createContextLoader();
if (this.contextLoader == null) {
this.contextLoader = this;
}
this.contextLoader.initWebApplicationContext(event.getServletContext());
}9
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ContextLoaderListener.java extends ContextLoader implements ServletContextListener
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public void contextInitialized(ServletContextEvent event) {
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this.contextLoader = createContextLoader();
5
if (this.contextLoader == null) {
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this.contextLoader = this;
7
}
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this.contextLoader.initWebApplicationContext(event.getServletContext());
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}
从这里开始，Spring 将会进行 Bean Definition的解析、Bean Processors 设置和处理、Beans 实例化等工作。从而将程序会用到的 Java 对象定义并根据该定义创建好，提供给开发人员去使用。
这里 Spring 首先需要处理的就是 Bean 的定义。经过不断的发展和演化，Bean 的定义方式有：
- 基于 XML 文件的配置方式
- 基于 Annotation 的配置方式
- 基于 Java Code 的配置方式
- 用户自定义的配置方式
这里就基于 XML 配置 Bean Definition 的源码进行解读学习
2、监听器都做了些什么？
Servlet 容器启动时如果 web.xml 配置了 ContextLoaderListener，则会调用该对象的初始化方法。根据 Java 语法规定，ContextLoaderListener 的父类 ContextLoader 有一段 static 的代码会更早被执行。
ContextLoader.java
static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
//private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
}
}15
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ContextLoader.java
2
3
static {
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// Load default strategy implementations from properties file.
5
// This is currently strictly internal and not meant to be customized
6
// by application developers.
7
try {
8
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
9
//private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
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defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
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}
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catch (IOException ex) {
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throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
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}
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}
这里的ContextLoader.properties（spring-web-x.x.x.RELEASE.jar --> org.springframework.web.context.support --> ContextLoader.properties）内容为
ContextLoader.properties
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext3
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ContextLoader.properties
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org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext
这段代码配置了 XML 默认使用的 Context 为 org.springframework.web.context.WebApplicationContext = org.springframework.web.context.support.XmlWebApplicationContext。根据该定义，如果开发人员没有从 web.xml 指定 contextClass 参数，则默认使用 XmlWebApplicationContext 作为 root WebApplicationContext 工具类。
好了，我们回到刚才的核心方法 initWebApplicationContext() 中去，在这个方法中，有个核心方法
ContextLoader.java
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
this.context = createWebApplicationContext(servletContext, parent);5
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ContextLoader.java
2
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// Store context in local instance variable, to guarantee that
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// it is available on ServletContext shutdown.
5
this.context = createWebApplicationContext(servletContext, parent);
我们再继续往里探索
ContextLoader.java
protected WebApplicationContext createWebApplicationContext(ServletContext sc, ApplicationContext parent) {
//step1
Class<?> contextClass = determineContextClass(sc);
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
//step2
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// Assign the best possible id value.
if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {
// Servlet <= 2.4: resort to name specified in web.xml, if any.
String servletContextName = sc.getServletContextName();
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(servletContextName));
}
else {
// Servlet 2.5's getContextPath available!
try {
String contextPath = (String) ServletContext.class.getMethod("getContextPath").invoke(sc);
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(contextPath));
}
catch (Exception ex) {
throw new IllegalStateException("Failed to invoke Servlet 2.5 getContextPath method", ex);
}
}
//step3
wac.setParent(parent);
wac.setServletContext(sc);
wac.setConfigLocation(sc.getInitParameter(CONFIG_LOCATION_PARAM));
customizeContext(sc, wac);
//step4
wac.refresh();
return wac;
}43
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ContextLoader.java
2
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protected WebApplicationContext createWebApplicationContext(ServletContext sc, ApplicationContext parent) {
4
//step1
5
Class<?> contextClass = determineContextClass(sc);
6
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
7
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
8
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
9
}
10
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//step2
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ConfigurableWebApplicationContext wac =
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(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
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// Assign the best possible id value.
16
if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {
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// Servlet <= 2.4: resort to name specified in web.xml, if any.
18
String servletContextName = sc.getServletContextName();
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wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
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ObjectUtils.getDisplayString(servletContextName));
21
}
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else {
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// Servlet 2.5's getContextPath available!
24
try {
25
String contextPath = (String) ServletContext.class.getMethod("getContextPath").invoke(sc);
26
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
27
ObjectUtils.getDisplayString(contextPath));
28
}
29
catch (Exception ex) {
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throw new IllegalStateException("Failed to invoke Servlet 2.5 getContextPath method", ex);
31
}
32
}
33
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//step3
35
wac.setParent(parent);
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wac.setServletContext(sc);
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wac.setConfigLocation(sc.getInitParameter(CONFIG_LOCATION_PARAM));
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customizeContext(sc, wac);
39
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//step4
41
wac.refresh();
42
return wac;
43
}
3、createWebApplicationContext
3.1 //step1
Class<?> contextClass = determineContextClass(sc);
ContextLoader.java
protected Class<?> determineContextClass(ServletContext servletContext) {
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM); //CONTEXT_CLASS_PARAM = "contextClass"
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
else {
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
//defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); defaultStrategies也就是静态代码块中初始化的默认工具类XmlWebApplicationContext
try {
return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}25
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ContextLoader.java
2
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protected Class<?> determineContextClass(ServletContext servletContext) {
4
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM); //CONTEXT_CLASS_PARAM = "contextClass"
5
if (contextClassName != null) {
6
try {
7
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
8
}
9
catch (ClassNotFoundException ex) {
10
throw new ApplicationContextException(
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"Failed to load custom context class [" + contextClassName + "]", ex);
12
}
13
}
14
else {
15
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
16
//defaultStrategies = PropertiesLoaderUtils.loadProperties(resource); defaultStrategies也就是静态代码块中初始化的默认工具类XmlWebApplicationContext
17
try {
18
return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
19
}
20
catch (ClassNotFoundException ex) {
21
throw new ApplicationContextException(
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"Failed to load default context class [" + contextClassName + "]", ex);
23
}
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}
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}
首先determineContextClass()方法查明具体的Context类，他会读取servletContext的初始化参数contextClass，此参数我们一般不配置。
所以Spring就会读取跟org.springframework.web.context.WebApplicationContext同一个包下面的ContextLoader.properties文件读取默认设置，反射出org.springframework.web.context.support.XmlWebApplicationContext类来。
以图友网项目为例（添加链接），此时返回的为 return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
3.2 //step2
ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
接下来就是通过BeanUtils的方法把新创建的XmlWebApplicationContext进行初始化。
注意看类别的变化
3.3 //step3
对于得到的这个 (ConfigurableWebApplicationContext) XmlWebApplicationContext
然后对之中的属性进行一系列的设置，首先会设置一个默认ID，即org.springframework.web.context.WebApplicationContext:+你项目的ContextPath。
然后再设置其他属性
wac.setParent(parent);
wac.setServletContext(sc);
其中还需要设置
wac.setConfigLocation(sc.getInitParameter(CONFIG_LOCATION_PARAM));
//CONFIG_LOCATION_PARAM = "contextConfigLocation"
//这里设置了你在web.xml中对于applicationContext.xml的地址配置
//e.g.
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:applicationContext.xml</param-value>
</context-param>4
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<context-param>
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<param-name>contextConfigLocation</param-name>
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<param-value>classpath:applicationContext.xml</param-value>
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</context-param>
也就是说，你在配置文件中的那些beans，这时候容器已经知道要准备哪些bean了，虽然还没有进行实例化，就像一个工厂已经得到了产品的加工图纸，但是还没有去加工实际产品出来。
customizeContext(sc, wac);
接下来就是customizeContext(sc, wac)方法，此方法会根据用户配置的globalInitializerClasses参数来初始化一些用户自定义的属性，一般我们不配置，所以这里什么也不做。
3.4 //step4
wac.refresh();
最后登场的就是最核心的方法了，在这个方法里，会完成资源文件的加载、配置文件解析、Bean定义的注册、组件的初始化等核心工作。
AbstractApplicationContext.java
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//此方法做一些准备工作，如记录开始时间，输出日志，initPropertySources();和getEnvironment().validateRequiredProperties();一般没干什么事
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//step4.1
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.
//step4.2
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
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;
}
}
}60
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AbstractApplicationContext.java
2
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@Override
4
public void refresh() throws BeansException, IllegalStateException {
5
synchronized (this.startupShutdownMonitor) {
6
// Prepare this context for refreshing.
7
//此方法做一些准备工作，如记录开始时间，输出日志，initPropertySources();和getEnvironment().validateRequiredProperties();一般没干什么事
8
prepareRefresh();
9
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// Tell the subclass to refresh the internal bean factory.
11
//step4.1
12
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
13
14
// Prepare the bean factory for use in this context.
15
prepareBeanFactory(beanFactory);
16
17
try {
18
// Allows post-processing of the bean factory in context subclasses.
19
postProcessBeanFactory(beanFactory);
20
21
// Invoke factory processors registered as beans in the context.
22
invokeBeanFactoryPostProcessors(beanFactory);
23
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// Register bean processors that intercept bean creation.
25
registerBeanPostProcessors(beanFactory);
26
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// Initialize message source for this context.
28
initMessageSource();
29
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// Initialize event multicaster for this context.
31
initApplicationEventMulticaster();
32
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// Initialize other special beans in specific context subclasses.
34
onRefresh();
35
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// Check for listener beans and register them.
37
registerListeners();
38
39
// Instantiate all remaining (non-lazy-init) singletons.
40
//step4.2
41
finishBeanFactoryInitialization(beanFactory);
42
43
// Last step: publish corresponding event.
44
finishRefresh();
45
}
46
47
catch (BeansException ex) {
48
logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);
49
50
// Destroy already created singletons to avoid dangling resources.
51
destroyBeans();
52
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// Reset 'active' flag.
54
cancelRefresh(ex);
55
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// Propagate exception to caller.
57
throw ex;
58
}
59
}
60
}
3.4.1 //step4.1 refresh()的核心 obtainFreshBeanFactory()
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
初始化BeanFactory，是整个refresh()方法的核心，其中完成了配置文件的加载、解析、注册。
AbstractApplicationContext.java
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}10
1
AbstractApplicationContext.java
2
3
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
4
refreshBeanFactory();
5
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
6
if (logger.isDebugEnabled()) {
7
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
8
}
9
return beanFactory;
10
}
跟进一下refreshBeanFactory();
AbstractRefreshableApplicationContext.java
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);
}
}20
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AbstractRefreshableApplicationContext.java
2
3
protected final void refreshBeanFactory() throws BeansException {
4
if (hasBeanFactory()) {
5
destroyBeans();
6
closeBeanFactory();
7
}
8
try {
9
DefaultListableBeanFactory beanFactory = createBeanFactory();
10
beanFactory.setSerializationId(getId());
11
customizeBeanFactory(beanFactory);
12
loadBeanDefinitions(beanFactory);
13
synchronized (this.beanFactoryMonitor) {
14
this.beanFactory = beanFactory;
15
}
16
}
17
catch (IOException ex) {
18
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
19
}
20
}
DefaultListableBeanFactory beanFactory = createBeanFactory();
在这个beanFactory中有个beanDefinitionMap，此时size=0
再跟进loadBeanDefinitions(beanFactory);
AbstractXmlApplicationContext.java
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
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.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}17
1
AbstractXmlApplicationContext.java
2
3
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
4
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
5
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
6
7
// Configure the bean definition reader with this context's
8
// resource loading environment.
9
beanDefinitionReader.setEnvironment(this.getEnvironment());
10
beanDefinitionReader.setResourceLoader(this);
11
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
12
13
// Allow a subclass to provide custom initialization of the reader,
14
// then proceed with actually loading the bean definitions.
15
initBeanDefinitionReader(beanDefinitionReader);
16
loadBeanDefinitions(beanDefinitionReader);
17
}
我们跟进这个方法
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
reader.loadBeanDefinitions(configLocation);
}
}
}8
1
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
2
String[] configLocations = getConfigLocations();
3
if (configLocations != null) {
4
for (String configLocation : configLocations) {
5
reader.loadBeanDefinitions(configLocation);
6
}
7
}
8
}
在3.3中我们提到，configLocations已经被得到，那么此时可以看到：
这里设计了层层调用，有很多重载方法，主要就是加载Spring所有的配置文件（可能会有多个），以备后面解析，注册之用。
然后追踪到 org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(Element root) 中
DefaultBeanDefinitionDocumentReader.java
protected void doRegisterBeanDefinitions(Element root) {
// Any nested <beans> elements will cause recursion in this method. In
// order to propagate and preserve <beans> 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(this.readerContext, root, parent);
if (this.delegate.isDefaultNamespace(root)) {
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
if (StringUtils.hasText(profileSpec)) {
Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
if (!this.environment.acceptsProfiles(specifiedProfiles)) {
return;
}
}
}
preProcessXml(root);
//xml解析和加载类
parseBeanDefinitions(root, this.delegate);
postProcessXml(root);
this.delegate = parent;
}32
1
DefaultBeanDefinitionDocumentReader.java
2
3
protected void doRegisterBeanDefinitions(Element root) {
4
// Any nested <beans> elements will cause recursion in this method. In
5
// order to propagate and preserve <beans> default-* attributes correctly,
6
// keep track of the current (parent) delegate, which may be null. Create
7
// the new (child) delegate with a reference to the parent for fallback purposes,
8
// then ultimately reset this.delegate back to its original (parent) reference.
9
// this behavior emulates a stack of delegates without actually necessitating one.
10
BeanDefinitionParserDelegate parent = this.delegate;
11
this.delegate = createDelegate(this.readerContext, root, parent);
12
13
if (this.delegate.isDefaultNamespace(root)) {
14
String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
15
if (StringUtils.hasText(profileSpec)) {
16
Assert.state(this.environment != null, "Environment must be set for evaluating profiles");
17
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
18
profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
19
if (!this.environment.acceptsProfiles(specifiedProfiles)) {
20
return;
21
}
22
}
23
}
24
25
preProcessXml(root);
26
27
//xml解析和加载类
28
parseBeanDefinitions(root, this.delegate);
29
postProcessXml(root);
30
31
this.delegate = parent;
32
}
BeanDefinitionParserDelegate parent = this.delegate;
这里创建了一个BeanDefinitionParserDelegate实例，解析XML的过程就是委托它完成的。实际上你跟进该类，可以发现里面定义了大量的常量，这些常量实际上就是我们在xml中使用到的节点和属性名。
e.g.
...
public static final String PROPERTY_ELEMENT = "property";
public static final String REF_ATTRIBUTE = "ref";
public static final String VALUE_ATTRIBUTE = "value";
...9
1
...
2
3
public static final String PROPERTY_ELEMENT = "property";
4
5
public static final String REF_ATTRIBUTE = "ref";
6
7
public static final String VALUE_ATTRIBUTE = "value";
8
9
...
这里的delegate实际上也是 BeanDefinitionParserDelegate 类，所以我们看到，在 parseBeanDefinitions(root, this.delegate); 中，是将该类作为一个参数引入了方法，实际上，它在方法中就发挥着解析xml的作用。
//xml解析和加载类
parseBeanDefinitions(root, this.delegate);
DefaultBeanDefinitionDocumentReader.java
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
if (delegate.isDefaultNamespace(root)) {
NodeList nl = root.getChildNodes(); //将节点获取存入collection
for (int i = 0; i < nl.getLength(); i++) { //对collection中存储的节点进行依次遍历
Node node = nl.item(i); //返回当前序号的节点
if (node instanceof Element) { //判断节点是否属于元素类（我们不需要文本型）（参考文章《Java是如何解析xml文件的（DOM）》）
Element ele = (Element) node;
//判断是否为默认的命名空间，其实就是根据配置文件的命名空间来判定
//如果是beans下的则认为是默认的命名空间，如果不是则认为是自定义的，我们使用的Aop、Tx等都是属于自定义标签的范畴
if (delegate.isDefaultNamespace(ele)) {
parseDefaultElement(ele, delegate); //进行解析
}
else {
delegate.parseCustomElement(ele);
}
}
}
}
else {
delegate.parseCustomElement(root);
}
}24
1
DefaultBeanDefinitionDocumentReader.java
2
3
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
4
if (delegate.isDefaultNamespace(root)) {
5
NodeList nl = root.getChildNodes(); //将节点获取存入collection
6
for (int i = 0; i < nl.getLength(); i++) { //对collection中存储的节点进行依次遍历
7
Node node = nl.item(i); //返回当前序号的节点
8
if (node instanceof Element) { //判断节点是否属于元素类（我们不需要文本型）（参考文章《Java是如何解析xml文件的（DOM）》）
9
Element ele = (Element) node;
10
//判断是否为默认的命名空间，其实就是根据配置文件的命名空间来判定
11
//如果是beans下的则认为是默认的命名空间，如果不是则认为是自定义的，我们使用的Aop、Tx等都是属于自定义标签的范畴
12
if (delegate.isDefaultNamespace(ele)) {
13
parseDefaultElement(ele, delegate); //进行解析
14
}
15
else {
16
delegate.parseCustomElement(ele);
17
}
18
}
19
}
20
}
21
else {
22
delegate.parseCustomElement(root);
23
}
24
}
最终，我们可以看到解析XML的是 parseDefaultElement(ele, delegate); 方法，它会判断并调用对应的解析，这里我们是bean
DefaultBeanDefinitionDocumentReader.java
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
// recurse
doRegisterBeanDefinitions(ele);
}
}17
1
DefaultBeanDefinitionDocumentReader.java
2
3
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
4
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
5
importBeanDefinitionResource(ele);
6
}
7
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
8
processAliasRegistration(ele);
9
}
10
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
11
processBeanDefinition(ele, delegate);
12
}
13
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
14
// recurse
15
doRegisterBeanDefinitions(ele);
16
}
17
}
然后进一步
DefaultBeanDefinitionDocumentReader.java
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.
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));
}
}18
1
DefaultBeanDefinitionDocumentReader.java
2
3
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
4
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
5
if (bdHolder != null) {
6
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
7
try {
8
// Register the final decorated instance.
9
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
10
}
11
catch (BeanDefinitionStoreException ex) {
12
getReaderContext().error("Failed to register bean definition with name '" +
13
bdHolder.getBeanName() + "'", ele, ex);
14
}
15
// Send registration event.
16
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
17
}
18
}
这个方法如果进一步深入，你可以发现它实际上最核心的两个步骤是：
- 把beanName放到队列里
- 把BeanDefinition放到map中
（关于这段注册bean的方法的源码跟进，可以参考博文：《Spring Ioc 源码分析(四)--parseBeanDefinitions()与BeanDefinitionParserDelegate》）
好了，执行完 parseBeanDefinitions 这个方法，我们看看现在的 delegate 里面多了些什么？
到此，bean的注册就完成了（当然，这里是指所有的bean都注册完）。在后面实例化的时候，就是把beanDefinitionMap中的BeanDefinition取出来，逐一实例化。
obtainFreshBeanFactory() 总算结束了，我们继续看refresh()方法中另一个核心方法，它是将bean进行实例化的重要角色。
3.4.2 //step4.2 refresh()的核心finishBeanFactoryInitialization(beanFactory);
我想到这里估计已经晕乎了，如果不太清楚我们现在走到了哪里，请查看目录中的 3.4 //step4
经过obtainFreshBeanFactory() 这个方法，我们的beanFactory就准备好了，接下来我们主要围绕finishBeanFactoryInitialization(beanFactory)方法，聊聊Spring是如何实例化bean的。
AbstractApplicationContext.java
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}25
1
AbstractApplicationContext.java
2
3
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
4
// Initialize conversion service for this context.
5
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
6
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
7
beanFactory.setConversionService(
8
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
9
}
10
11
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
12
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
13
for (String weaverAwareName : weaverAwareNames) {
14
getBean(weaverAwareName);
15
}
16
17
// Stop using the temporary ClassLoader for type matching.
18
beanFactory.setTempClassLoader(null);
19
20
// Allow for caching all bean definition metadata, not expecting further changes.
21
beanFactory.freezeConfiguration();
22
23
// Instantiate all remaining (non-lazy-init) singletons.
24
beanFactory.preInstantiateSingletons();
25
}
这个方法，就是为了实例化非懒加载的单例bean，我们走进 beanFactory.preInstantiateSingletons(); 看一看
（注意，这里实例化单例，而Struts中Action是每次请求都创建，所以Action并不是单例的）
DefaultListableBeanFactory.java
public void preInstantiateSingletons() throws BeansException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Pre-instantiating singletons in " + this);
}
List<String> beanNames;
synchronized (this.beanDefinitionMap) {
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
beanNames = new ArrayList<String>(this.beanDefinitionNames);
}
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) { //将加载进来的beanDefinitionNames循环分析
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //如果不是抽象类, 且是单例, 且不是延迟加载
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
smartSingleton.afterSingletonsInstantiated();
return null;
}
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}x
1
DefaultListableBeanFactory.java
2
3
public void preInstantiateSingletons() throws BeansException {
4
if (this.logger.isDebugEnabled()) {
5
this.logger.debug("Pre-instantiating singletons in " + this);
6
}
7
8
List<String> beanNames;
9
synchronized (this.beanDefinitionMap) {
10
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
11
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
12
beanNames = new ArrayList<String>(this.beanDefinitionNames);
13
}
14
15
// Trigger initialization of all non-lazy singleton beans...
16
for (String beanName : beanNames) { //将加载进来的beanDefinitionNames循环分析
17
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
18
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //如果不是抽象类, 且是单例, 且不是延迟加载
19
if (isFactoryBean(beanName)) {
20
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
21
boolean isEagerInit;
22
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
23
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
24
@Override
25
public Boolean run() {
26
return ((SmartFactoryBean<?>) factory).isEagerInit();
27
}
28
}, getAccessControlContext());
29
}
30
else {
31
isEagerInit = (factory instanceof SmartFactoryBean &&
32
((SmartFactoryBean<?>) factory).isEagerInit());
33
}
34
if (isEagerInit) {
35
getBean(beanName);
36
}
37
}
38
else {
39
getBean(beanName);
40
}
41
}
42
}
43
44
// Trigger post-initialization callback for all applicable beans...
45
for (String beanName : beanNames) {
46
Object singletonInstance = getSingleton(beanName);
47
if (singletonInstance instanceof SmartInitializingSingleton) {
48
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
49
if (System.getSecurityManager() != null) {
50
AccessController.doPrivileged(new PrivilegedAction<Object>() {
51
@Override
52
public Object run() {
53
smartSingleton.afterSingletonsInstantiated();
54
return null;
55
}
56
}, getAccessControlContext());
57
}
58
else {
59
smartSingleton.afterSingletonsInstantiated();
60
}
61
}
62
}
63
}
因为Struts项目中Action并不满足条件 “不是抽象类, 且是单例, 且不是延迟加载”，所以该方法对我们自定义的Action几乎没有用，我们一直循环直到单例的对象出现，再来看这个代码。
我们把这小段代码提出来单独看
for (String beanName : beanNames) { //将加载进来的beanDefinitionNames循环分析
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //如果不是抽象类, 且是单例, 且不是延迟加载
if (isFactoryBean(beanName)) { //是否实现FactoryBean接口
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}1
for (String beanName : beanNames) { //将加载进来的beanDefinitionNames循环分析
2
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
3
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { //如果不是抽象类, 且是单例, 且不是延迟加载
4
if (isFactoryBean(beanName)) { //是否实现FactoryBean接口
5
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
6
boolean isEagerInit;
7
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
8
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
9
@Override
10
public Boolean run() {
11
return ((SmartFactoryBean<?>) factory).isEagerInit();
12
}
13
}, getAccessControlContext());
14
}
15
else {
16
isEagerInit = (factory instanceof SmartFactoryBean &&
17
((SmartFactoryBean<?>) factory).isEagerInit());
18
}
19
if (isEagerInit) {
20
getBean(beanName);
21
}
22
}
23
else {
24
getBean(beanName);
25
}
26
}
27
}
- 判断这个bean是否是抽象类，是否是单例，是否延迟加载
- 如果不是抽象类, 且是单例, 且不是延迟加载，那么判断是否实现 FactoryBean 接口
- 如果实现了 FactoryBean，则 getBean(FACTORY_BEAN_PREFIX + beanName)，否则 getBean(beanName)
（参考链接：）
如果我们跟进 getBean 这个方法，发现它调用了 doGetBean 这个方法，我们再跟进，这个方法非常长（这里就不贴出来了）
在这个方法中，你可以不断地去跟进（这里不再做具体展开），你会发现大概的步骤差不多是
- 创建一个bean的实例
- 将这个实例封装到BeanWrapper中
而这里bean的实例化方法，其实是 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
这个instantiate 方法在 package org.springframework.beans.factory.support; --> SimpleInstantiationStrategy.java
在这之中采用反射机制将对象进行了实例化。
其实还涉及到bean实例化以后，Spring是如何将bean的属性进行注入的，这里暂时不做进一步的展开了。
可以知道的是，最终属性的注入是利用反射机制，通过setter赋值的。
4、参考链接
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