spring加载基本的xml配置
最简单的xml配置,并使用ClassPathXmlApplicationContext加载
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean class="com.forcht.test.SimpleBean"/>
beans>
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
SimpleBean simpleBean = applicationContext.getBean(SimpleBean.class);
simpleBean.send();
}
查看ClassPathXmlApplicationContext的继承关系
通过断点debug跟踪源码
ClassPathXmlApplicationContext构造器源码,不断调用父类的构造器直到AbstractApplicationContext
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();
}
}
查看AbstractApplicationContext构造器源码
public AbstractApplicationContext(ApplicationContext parent) {
this();
setParent(parent);
}
public AbstractApplicationContext() {
this.resourcePatternResolver = getResourcePatternResolver();
}
//该方法创建一个资源处理器
protected ResourcePatternResolver getResourcePatternResolver() {
return new PathMatchingResourcePatternResolver(this);
}
到目前为止,ClassPathXmlApplicationContext已经有了两个资源加载器(一个由AbstractApplicationContext继承DefaultResourceLoader而来,一个是AbstractApplicationContext主动创建的PathMatchingResourcePatternResolver)
DefaultResourceLoader只能加载一个特定类路径的资源,PathMatchingResourcePatternResolver可以根据Ant风格加载多个资源。
每个父类的构造方法返回后调用AbstractRefreshableConfigApplicationContext的setConfigLocations(configLocations)方法
此方法的目的在于将占位符(placeholder)解析成实际的地址
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;
}
}
protected String resolvePath(String path) {
return getEnvironment().resolveRequiredPlaceholders(path);
}
getEnvironment()方法是由ConfigurableApplicationContext接口定义,在AbstractApplicationContext实现,其实就是判断environment 是否为空,不为空就创建一个StandardEnvironment
@Override
public ConfigurableEnvironment getEnvironment() {
if (this.environment == null) {
this.environment = createEnvironment();
}
return this.environment;
}
protected ConfigurableEnvironment createEnvironment() {
return new StandardEnvironment();
}
Spring bean解析就在refresh方法,Spring所有的初始化都在这个方法中完成,该方法在AbstractApplicationContext实现
@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();
}
}
}
//fresh准备工作,包括设置启动时间,是否激活标识位,初始化属性源(property source)配置
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if (logger.isInfoEnabled()) {
logger.info("Refreshing " + this);
}
// Initialize any placeholder property sources in the context environment
//该方法是空方法
initPropertySources();
// Validate that all properties marked as required are resolvable
// see ConfigurablePropertyResolver#setRequiredProperties
//属性校验
getEnvironment().validateRequiredProperties();
// Allow for the collection of early ApplicationEvents,
// to be published once the multicaster is available...
this.earlyApplicationEvents = new LinkedHashSet();
}
创建beanFactory
调用AbstractApplicationContext的obtainFreshBeanFactory方法获取obtainFreshBeanFactory
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//该方法在AbstractRefreshableApplicationContext实现
refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {
logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
}
return beanFactory;
}
refreshBeanFactory方法
@Override
protected final void refreshBeanFactory() throws BeansException {
//如果已经存在的BeanFactory则销毁
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
//创建一个DefaultListableBeanFactory
DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
//定制beanFactory,由AbstractRefreshableApplicationContext实现
customizeBeanFactory(beanFactory);
//加载bean,由AbstractXmlApplicationContext实现
loadBeanDefinitions(beanFactory);
synchronized (this.beanFactoryMonitor) {
this.beanFactory = beanFactory;
}
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
定制bean,customizeBeanFactory方法实现
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
if (this.allowBeanDefinitionOverriding != null) {
beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.allowCircularReferences != null) {
beanFactory.setAllowCircularReferences(this.allowCircularReferences);
}
}
加载bean
@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);
}