Dubbo源码解析：基于Extensible XML authoring 扩展Spring XML元素_小识的博客

步骤

1. 编写XML Schema文件，定义XML结构
2. 自定义NamespaceHandler实现
3. 自定义BeanDefinitionParser，将XML解析为BeanDefinition
4. 注册到Spring容器

扩展Spring XML元素

项目结构如下

编写XML Schema文件

@Data
@ToString
public class User {

    private Long id;
    private String name;

}

users.xsd

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xsd:schema xmlns="http://www.javashitang.com/schema/users"
            xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            targetNamespace="http://www.javashitang.com/schema/users">

    <xsd:import namespace="http://www.w3.org/XML/1998/namespace"/>

    <!-- 定义 User 类型（复杂类型） -->
    <xsd:complexType name="User">
        <xsd:attribute name="id" type="xsd:long" use="required"/>
        <xsd:attribute name="name" type="xsd:string" use="required"/>
    </xsd:complexType>


    <!-- 定义 user 元素 -->
    <xsd:element name="user" type="User"/>
</xsd:schema>

自定义NamespaceHandler实现

public class UsersNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("user", new UserBeanDefinitionParser());
    }
}

自定义BeanDefinitionParser

public class UserBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {

    @Override
    protected Class<?> getBeanClass(Element element) {
        return User.class;
    }

    @Override
    protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
        setPropertyValue("id", element, builder);
        setPropertyValue("name", element, builder);
    }

    private void setPropertyValue(String attributeName, Element element, BeanDefinitionBuilder builder) {
        String attributeValue = element.getAttribute(attributeName);
        if (StringUtils.hasText(attributeValue)) {
            builder.addPropertyValue(attributeName, attributeValue);

        }
    }
}

注册到Spring容器

spring.handlers

## 定义 namespace 与 NamespaceHandler 的映射
http\://www.javashitang.com/schema/users=com.javashitang.UsersNamespaceHandler

spring.schemas

http\://www.javashitang.com/schema/users.xsd=META-INF/users.xsd

测试

users-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:users="http://www.javashitang.com/schema/users"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.javashitang.com/schema/users
        http://www.javashitang.com/schema/users.xsd">

    <users:user id="1" name="小识"/>

</beans>

public class ExtensibleXmlAuthoringDemo {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/users-context.xml");
        context.refresh();
        // User(id=1, name=小识)
        System.out.println(context.getBean(User.class));
    }
}

参考博客

[1]https://www.jianshu.com/p/8639e5e9fba6
[2]https://www.cnblogs.com/lifullmoon/p/14449414.html