在一个spring xml配置文件中，NamespaceHandler是DefaultBeanDefinitionDocumentReader用来处理自定义命名空间的基础接口。其层次结构如下：
<context>为开头的标签统一在ContextNamespaceHandler中进行解析，ContextNamespaceHandler继承了NamespaceHandlerSupport，实现了NamespaceHandler接口。其解析的标签有：
@Override
public void init() {
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());
}
本文主要讲property-placeholder和property-override。
annotation-config和component-scan在这篇文章中进行了讲解，其它在后面的序列中会讲到。
1. property-placeholder
解析流程图如下：
解析过程如下：
>>DefaultBeanDefinitionDocumentReader读取xml配置文件，调用BeanDefinitionParserDelegate代理的parseCustomElement方法
>>BeanDefinitionParserDelegate调用NamespaceHandler的parse方法解析配置文件。
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
String namespaceUri = getNamespaceURI(ele);
NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
if (handler == null) {
error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
return null;
}
return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}
>>NamespaceHandler调用NamespaceHandlerSupport的parse方法
/**
* Parses the supplied {@link Element} by delegating to the {@link BeanDefinitionParser} that is
* registered for that {@link Element}.
*/
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
return findParserForElement(element, parserContext).parse(element, parserContext);
}
NamespaceHandlerSupport调用AbstractBeanDefinitionParser的parse方法，解析id和name
@Override
public final BeanDefinition parse(Element element, ParserContext parserContext) {
AbstractBeanDefinition definition = parseInternal(element, parserContext);
if (definition != null && !parserContext.isNested()) {
try {
String id = resolveId(element, definition, parserContext);
if (!StringUtils.hasText(id)) {
parserContext.getReaderContext().error(
"Id is required for element '" + parserContext.getDelegate().getLocalName(element)
+ "' when used as a top-level tag", element);
}
String[] aliases = new String[0];
String name = element.getAttribute(NAME_ATTRIBUTE);
if (StringUtils.hasLength(name)) {
aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
}
BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
registerBeanDefinition(holder, parserContext.getRegistry());
if (shouldFireEvents()) {
BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
postProcessComponentDefinition(componentDefinition);
parserContext.registerComponent(componentDefinition);
}
}
catch (BeanDefinitionStoreException ex) {
parserContext.getReaderContext().error(ex.getMessage(), element);
return null;
}
}
return definition;
}
>>调用AbstractSingleBeanDefinitionParser的parseInternal方法
/**
* Creates a {@link BeanDefinitionBuilder} instance for the
* {@link #getBeanClass bean Class} and passes it to the
* {@link #doParse} strategy method.
* @param element the element that is to be parsed into a single BeanDefinition
* @param parserContext the object encapsulating the current state of the parsing process
* @return the BeanDefinition resulting from the parsing of the supplied {@link Element}
* @throws IllegalStateException if the bean {@link Class} returned from
* {@link #getBeanClass(org.w3c.dom.Element)} is {@code null}
* @see #doParse
*/
@Override
protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
String parentName = getParentName(element);
if (parentName != null) {
builder.getRawBeanDefinition().setParentName(parentName);
}
Class<?> beanClass = getBeanClass(element);
if (beanClass != null) {
builder.getRawBeanDefinition().setBeanClass(beanClass);
}
else {
String beanClassName = getBeanClassName(element);
if (beanClassName != null) {
builder.getRawBeanDefinition().setBeanClassName(beanClassName);
}
}
builder.getRawBeanDefinition().setSource(parserContext.extractSource(element));
if (parserContext.isNested()) {
// Inner bean definition must receive same scope as containing bean.
builder.setScope(parserContext.getContainingBeanDefinition().getScope());
}
if (parserContext.isDefaultLazyInit()) {
// Default-lazy-init applies to custom bean definitions as well.
builder.setLazyInit(true);
}
doParse(element, parserContext, builder);
return builder.getBeanDefinition();
}
>>调用
PropertyPlaceholderBeanDefinitionParser
的doParse方法
/**
* Parser for the {@code <context:property-placeholder/>} element.
*
* @author Juergen Hoeller
* @author Dave Syer
* @author Chris Beams
* @since 2.5
*/
class PropertyPlaceholderBeanDefinitionParser extends AbstractPropertyLoadingBeanDefinitionParser { private static final String SYSTEM_PROPERTIES_MODE_ATTRIB = "system-properties-mode";
private static final String SYSTEM_PROPERTIES_MODE_DEFAULT = "ENVIRONMENT"; @Override
protected Class<?> getBeanClass(Element element) {
// As of Spring 3.1, the default value of system-properties-mode has changed from
// 'FALLBACK' to 'ENVIRONMENT'. This latter value indicates that resolution of
// placeholders against system properties is a function of the Environment and
// its current set of PropertySources
if (element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIB).equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
return PropertySourcesPlaceholderConfigurer.class;
} // the user has explicitly specified a value for system-properties-mode. Revert
// to PropertyPlaceholderConfigurer to ensure backward compatibility.
return PropertyPlaceholderConfigurer.class;
} @Override
protected void doParse(Element element, BeanDefinitionBuilder builder) {
super.doParse(element, builder); builder.addPropertyValue("ignoreUnresolvablePlaceholders",
Boolean.valueOf(element.getAttribute("ignore-unresolvable"))); String systemPropertiesModeName = element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIB);
if (StringUtils.hasLength(systemPropertiesModeName) &&
!systemPropertiesModeName.equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
builder.addPropertyValue("systemPropertiesModeName", "SYSTEM_PROPERTIES_MODE_"+systemPropertiesModeName);
}
}}
其中，
PropertyPlaceholderConfigurer
PropertyPlaceholderConfigurer是PlaceholderConfigurerSupport的实现类，解析占位符setLoaction、setProperties设置的local、properties和系统属性。
从spring3.1 org.springframework.context.support.PropertySourcesPlaceholderConfigurer请比这个实现被更广泛的使用。因为PropertySourcesPlaceholderConfigurer灵活的使用org.springframework.core.env.Environment，并且它的org.springframework.core.env.PropertySource机制也在spring 3.1中可用了。
但PropertyPlaceholderConfigurer在以下场景还是比较有优势的：
spring-context模块api不可用(例如仅仅使用spring的BeanFactory)，不能像ApplicationContext那样使用。
使用setSystemPropertiesMode(int)或者SetSystemPropertiesModeName(String)设置属性的已经存在的配置。鼓励开发者放弃使用这些设置方式，而不是通过容器的Environment来配置property source；然而，这些功能的维护仍然需要继续使用propertyPlaceholderConfigurer。
PropertySourcesPlaceholderConfigurer
PropertySourcesPlaceholderConfigurer是org.springframework.beans.factory.config.PlaceholderConfigurerSupport的特殊实现，它解析bean定义内的${..}占位符和@Value注解的当前spring的Environment和PropertySource集合中的属性值。
这个类用来替换spring3.1应用及以后的PropertyPlaceholderConfigurer。默认情况下，它在spring-context-3.1.xsd中支持<property-placeholder>,同时为了保证spring-context的向后兼容性，3.0版本默认值仍然是PropertyPlaceholderConfigurer。
任意本地变量(如通过setProperties或者通过setLocation设置的)作为propertySource增加，本地属性的搜索优先级基于setLocalOverride设置的localOverride属性的值，localOverride默认值为false，即本地属性在所有Environment属性source之后被搜索。PropertyPlaceholderConfigurer是个bean工厂后置处理器的实现，也就是 BeanFactoryPostProcessor接口的一个实现。
/**
* {@inheritDoc}
* <p>Processing occurs by replacing ${...} placeholders in bean definitions by resolving each
* against this configurer's set of {@link PropertySources}, which includes:
* <ul>
* <li>all {@linkplain org.springframework.core.env.ConfigurableEnvironment#getPropertySources
* environment property sources}, if an {@code Environment} {@linkplain #setEnvironment is present}
* <li>{@linkplain #mergeProperties merged local properties}, if {@linkplain #setLocation any}
* {@linkplain #setLocations have} {@linkplain #setProperties been}
* {@linkplain #setPropertiesArray specified}
* <li>any property sources set by calling {@link #setPropertySources}
* </ul>
* <p>If {@link #setPropertySources} is called, <strong>environment and local properties will be
* ignored</strong>. This method is designed to give the user fine-grained control over property
* sources, and once set, the configurer makes no assumptions about adding additional sources.
*/
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
if (this.propertySources == null) {
this.propertySources = new MutablePropertySources();
if (this.environment != null) {
this.propertySources.addLast(
new PropertySource<Environment>(ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME, this.environment) {
@Override
public String getProperty(String key) {
return this.source.getProperty(key);
}
}
);
}
try {
PropertySource<?> localPropertySource =
new PropertiesPropertySource(LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME, mergeProperties());
if (this.localOverride) {
this.propertySources.addFirst(localPropertySource);
}
else {
this.propertySources.addLast(localPropertySource);
}
}
catch (IOException ex) {
throw new BeanInitializationException("Could not load properties", ex);
}
} processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));
this.appliedPropertySources = this.propertySources;
}
调用继续处理
/**
* Visit each bean definition in the given bean factory and attempt to replace ${...} property
* placeholders with values from the given properties.
*/
protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
final ConfigurablePropertyResolver propertyResolver) throws BeansException { propertyResolver.setPlaceholderPrefix(this.placeholderPrefix);
propertyResolver.setPlaceholderSuffix(this.placeholderSuffix);
propertyResolver.setValueSeparator(this.valueSeparator); StringValueResolver valueResolver = new StringValueResolver() {
@Override
public String resolveStringValue(String strVal) {
String resolved = ignoreUnresolvablePlaceholders ?
propertyResolver.resolvePlaceholders(strVal) :
propertyResolver.resolveRequiredPlaceholders(strVal);
return (resolved.equals(nullValue) ? null : resolved);
}
}; doProcessProperties(beanFactoryToProcess, valueResolver);
}
继续
protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
StringValueResolver valueResolver) { BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver); String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
for (String curName : beanNames) {
// Check that we're not parsing our own bean definition,
// to avoid failing on unresolvable placeholders in properties file locations.
if (!(curName.equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(curName);
try {
visitor.visitBeanDefinition(bd);
}
catch (Exception ex) {
throw new BeanDefinitionStoreException(bd.getResourceDescription(), curName, ex.getMessage(), ex);
}
}
} // New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
beanFactoryToProcess.resolveAliases(valueResolver); // New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
}
2. property-override
解析流程图
解析过程
>>其它流程和
>>调用
PropertyOverrideBeanDefinitionParser
的doParse方法
/**
* Parser for the <context:property-override/> element.
*
* @author Juergen Hoeller
* @author Dave Syer
* @since 2.5.2
*/
class PropertyOverrideBeanDefinitionParser extends AbstractPropertyLoadingBeanDefinitionParser { @Override
protected Class<?> getBeanClass(Element element) {
return PropertyOverrideConfigurer.class;
} @Override
protected void doParse(Element element, BeanDefinitionBuilder builder) { super.doParse(element, builder);
builder.addPropertyValue("ignoreInvalidKeys",
Boolean.valueOf(element.getAttribute("ignore-unresolvable"))); }}
小结
The PropertyPlaceholderConfigurer allows properties to be pulled in to the application context file.示例：
<bean id="propertyPlaceholderConfigurer"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>classpath:database.properties</value>
</list>
</property>
</bean><bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="user" value="${db.user}"/>
<property name="password" value="${db.password}"/>
...
</bean>
The PropertyOverrideConfigurer works in the opposite way, pushing properties from property files into properties in the context file (without having to specifically define a place holder – e.g. ${db.user}).
<?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-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd"> <bean class="org.springframework.beans.factory.config.PropertyOverrideConfigurer">
<property name="location" value="classpath:beanOverride.cfg" />
</bean>
<bean id="person" class="com.concretepage.Person" >
<property name="name" value="Ram"/>
<property name="age" value="20"/>
<property name="location" value="Varanasi"/>
</bean>
</beans>
参考文献
【1】http://www.summa.com/blog/2009/04/20/6-tips-for-managing-property-files-with-spring
【2】http://www.concretepage.com/spring/example_propertyoverrideconfigurer_spring
