Spring中property-placeholder的使用与解析详解

<?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:context="http://www.springframework.org/schema/context"
 xsi:schemaLocation="
  http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-4.2.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context-4.2.xsd">

  <context:property-placeholder location="classpath:foo.properties" />
</beans>

@Configuration
@PropertySource("classpath:foo.properties")
public class PropertiesWithJavaConfig {
 @Bean
 public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
  return new PropertySourcesPlaceholderConfigurer();
 }
}

@Value( "${jdbc.url}" )
private String jdbcUrl;

@Value( "${jdbc.url:aDefaultUrl}" )
private String jdbcUrl;

<bean id="dataSource">
 <property name="url" value="${jdbc.url}" />
</bean>

 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);
  }
 }

 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)) {
      parseDefaultElement(ele, delegate);
     }
     else {
      delegate.parseCustomElement(ele);
     }
    }
   }
  }
  else {
   delegate.parseCustomElement(root);
  }
 }

 @Override
 public void init() {
  // 这就是我们要找的解析器
  registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
  registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
  registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
  registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
  registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
  registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
  registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
  registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
 }

public interface BeanDefinitionParser {
BeanDefinition parse(Element element, ParserContext parserContext);
}

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
  PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
 }

 OrderComparator.sort(priorityOrderedPostProcessors);
 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);