spring xml 配置文件中标签的解析

一个springmvc配置文件的例子为：

<?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"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd">

    <description>spring Configuration</description>
    
    <mvc:annotation-driven />

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <context:component-scan base-package="org.xuan.springmvc.controller"
        use-default-filters="false"><!-- base-package 如果多个,用“,”分隔 -->
        <context:include-filter type="annotation"
            expression="org.springframework.stereotype.Controller" /> <!-- 子标签是用来添加扫描注解的 -->
    </context:component-scan>
</beans>

sprin读取到这个文件后是如何进行解析的呢？

首先这个xml包含了命名空间如：

xmlns:mvc="http://www.springframework.org/schema/mvc"

这个文件命名空间对应解析规则在spring-xxx-x.x.x.RELEASE.jar/META-INF/spring.handlers文件中，比如：

spring-web-4.3.7.RELEASE.jar/META-INF/spring.handlers

打开文件spring.handlers

http://www.springframework.org/schema/mvc=org.springframework.web.servlet.config.MvcNamespaceHandler

得到处理的类是MvcNamespaceHandler

然后在这个xml中还有一些标签如：

<mvc:annotation-driven />

这个标签对应解析配置就在MvcNamespaceHandler中，打开文件查看内容：

public class MvcNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
        registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
        registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
        registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
        registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
        registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("velocity-configurer", new VelocityConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());
    }

}

所以当读取到annotation-driven标签的时候就会去AnnotationDrivenBeanDefinitionParser中进行处理。