上节探讨了Spring IOC容器中getBean方法,下面我们将自行编写测试用例,深入跟踪分析bean对象创建过程。
测试示例代码如下:
- package org.springframework.context.mytests;
- import org.junit.Test;
- import org.springframework.context.ApplicationContext;
- import org.springframework.context.support.ClassPathXmlApplicationContext;
- public class ApplicationContextTest {
- @Test
- public void testApplicationContext() {
- ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
- System.out.println("numbers: " + applicationContext.getBeanDefinitionCount());
- ((Worker)applicationContext.getBean("worker")).work();
- }
- }
应用ClassPathXmlApplicationContext加载解析xml文件,xml配置文件如下:
- <?xml version="1.0" encoding="UTF-8"?>
- <beans xmlns="http://www.springframework.org/schema/beans"
- xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xmlns:p="http://www.springframework.org/schema/p"
- xmlns:context="http://www.springframework.org/schema/context"
- xmlns:util="http://www.springframework.org/schema/util"
- xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
- http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
- http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd">
- <bean id="worker" class="org.springframework.context.mytests.Worker"></bean>
- </beans>
bean Worker代码如下:
- package org.springframework.context.mytests;
- public class Worker {
- public void work() {
- System.out.println("I am working");
- }
- }
在IDE中对测试文件打断点,进入Debug模式,一步一步跟随程序跟踪bean创建过程。
跟踪断点,进入ClassPathXmlApplicationContext源码,如下所示:
- package org.springframework.context.support;
- import org.springframework.beans.BeansException;
- import org.springframework.context.ApplicationContext;
- import org.springframework.core.io.ClassPathResource;
- import org.springframework.core.io.Resource;
- import org.springframework.util.Assert;
- public class ClassPathXmlApplicationContext extends AbstractXmlApplicationContext {
- ......
- public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
- this(new String[] {
- configLocation
- },
- true, null);
- }
- ......
- public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
- super(parent);
- setConfigLocations(configLocations);
- if (refresh) {
- refresh();
- }
- }
- ......
- }
ClassPathXmlApplicationContex中都是构造器方法,表明加载解析xml文件的操作都是在实例化阶段完成的。以上是部分源码片段,在本测试中,调用第一个构造器初始化,但其实质是调用第二个构造器。从源码可以发现,第二个构造器实际上完成了两个主要功能:
,设置应用上下文的配置文件路径,如果没有设置,便会使用默认路径
- setConfigLocations(configLocations)
,IOC容器初始化入口
- refresh()
通过查找定位发现:
是继承于AbstractRefreshableConfigApplicationContext抽象类,其源码如下:
- setConfigLocations(configLocations)
- public void setConfigLocations(String...locations) {
- if (locations != null) {
- Assert.noNullElements(locations, "Config locations must not be null");
- this.configLocations = new String[locations.length];
- for (int i = 0; i < locations.length; i++) {
- this.configLocations[i] = resolvePath(locations[i]).trim();
- }
- } else {
- this.configLocations = null;
- }
- }
可以看到setConfigLocations方法获取定位信息首先需要调用resolvePath方法对路径进行预处理。
refresh方法是继承于AbstractApplicationContext抽象类,是在接口ConfigurableApplicationContext中定义的。其在抽象类中源码如下:
- @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.
- 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();
- }
- }
- }
refresh方法大致描述了Spring IOC容器的初始化过程,第一步
主要是做一些准备工作,如准备应用环境、设置启动时间、设置属性源初始化标志等。重点看第二步
- prepareRefresh
,这一步是获取更新后的子类Bean工厂。其源码如下:
- ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()
- /**
- * Tell the subclass to refresh the internal bean factory.
- * @return the fresh BeanFactory instance
- * @see #refreshBeanFactory()
- * @see #getBeanFactory()
- */
- protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
- refreshBeanFactory();
- ConfigurableListableBeanFactory beanFactory = getBeanFactory();
- if (logger.isDebugEnabled()) {
- logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
- }
- return beanFactory;
- }
其内部有两个方法
和
- refreshBeanFactory()
,这两个方法均为抽象方法,如下所示:
- getBeanFactory()
- protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;
- public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;
查找子类发现,这两个方法均在子类AbstractRefreshableApplicationContext中实现,该类仍然是抽象类。先来看refreshBeanFactory方法实现:
- @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);
- }
- }
该方法先判断是否存在BeanFactory,若存在则直接销毁原BeanFactory,先销毁工厂中的Beans,再关闭工bean厂。之后创建新的Bean工厂,其方法为
,如下所示:
- createBeanFactory
- protected DefaultListableBeanFactory createBeanFactory() {
- return new DefaultListableBeanFactory(getInternalParentBeanFactory());
- }
从函数返回值可以看出,重新创建的Bean工厂是默认的bean工厂
类型。创建完新的bean工厂后便会根据上下文进行初始化(customizeBeanFactory),加载bean定义(loadBeanDefinitions)。其中,loadBeanDefinitions为抽象方法,如下所示:
- DefaultListableBeanFactory
- protected abstract void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException,
- IOException;
该方法具体实现在AbstractXmlApplicationContext类中,该类仍然是一个抽象类,实现如下:
- @Override 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);
- }
阅读源码发现,方法内部是采用XmlBeanDefinitionReader来读取加载bean对象。通过追踪源码,发现XmlBeanDefinitionReader最终调用loadBeanDefinitions方法来读取加载bean,具体实现如下:
- 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!");
- }
- 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();
- }
- }
- }
到此,应该明白了IOC容器初始化bean工厂、加载bean对象的大致过程了。现在回头再来看obtainFreshBeanFactory方法中的另一个方法getBeanFactory方法。该方法在子类AbstractRefreshableApplicationContext中实现就相对简单写,如下所示:
- @Override
- public final ConfigurableListableBeanFactory getBeanFactory() {
- synchronized (this.beanFactoryMonitor) {
- if (this.beanFactory == null) {
- throw new IllegalStateException("BeanFactory not initialized or already closed - " +
- "call 'refresh' before accessing beans via the ApplicationContext");
- }
- return this.beanFactory;
- }
- }
到此为止,Spring IOC容器加载机制探讨基本上告一段落了。通过对源码分析,对Spring IOC机制能有一个大致的了解:1、解析、定位、加载xml配置文件;2、提取配置文件内容;3、新建bean工厂;4、创建Bean定义,并放入map中存储。通过追踪源码,也深刻体会到了spring对设计模式的应用。
下一节将进入对Spring另一大杀器的探讨,Spring-AOP。
来源: http://www.cnblogs.com/hthuang/p/7837730.html