Spring源码解析系列文章（X）——扩展Spring自定义标签

╰半橙微兮° 2023-07-18 02:28 1阅读 0赞

**目录**

1、创建承载自定义标签属性的类

2、创建XSD

3、创建解析XSD文件自定义标签的类

4、创建Handler

5、编写 spring.handlers 和 spring.schemas文件

spring.handlers

spring.schemas

6、引入自定义标签

7、验证

--------------------

# 1、创建承载自定义标签属性的类 #

package thinking.in.spring.boot.samples.spring5.customlabel;
    
    /**
     * 创建承载自定义标签属性的类
     */
    public class CustomLabel {
    
        private String id;
        private String name;
        private String value;
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getValue() {
            return value;
        }
    
        public void setValue(String value) {
            this.value = value;
        }
    }

# 2、创建XSD #

在maven工程 resources/META-INF/ 下创建 spring-custom.xsd 文件，内容如下

<?xml version="1.0" encoding="UTF-8"?>
    <schema xmlns="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.rh.com/schema/customLabel"
    xmlns:tns="http://www.rh.com/schema/customLabel"
    elementFormDefault="qualified">
        <element name="mybean">
            <complexType>
                <attribute name="id" type="string"/>
                <attribute name="name" type="string"/>
                <attribute name="value" type="string"/>
            </complexType>
        </element>
        <element name="tag2">
            <complexType>
                <attribute name="id" type="string"/>
                <attribute name="name" type="string"/>
                <attribute name="value" type="string"/>
            </complexType>
        </element>
    </schema>

# 3、创建解析XSD文件自定义标签的类 #

创建 CustomLabelBeanDefinitionParser 类，此类继承了AbstractSingleBeanDefinitionParser ，用于解析XSD自定义标签

package thinking.in.spring.boot.samples.spring5.customlabel;
    
    import org.springframework.beans.factory.support.BeanDefinitionBuilder;
    import org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser;
    import org.springframework.util.StringUtils;
    import org.w3c.dom.Element;
    
    
    public class CustomLabelBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
    
        // Element 对应的类
        protected Class getBeanClass(Element element) {
            return CustomLabel.class;
        }
    
        // 从 Element 中解析并提取对应的元素
        protected void doParse(Element element, BeanDefinitionBuilder bean) {
            String id = element.getAttribute("id");
            String name = element.getAttribute("name");
            String value = element.getAttribute("value");
            /**
             * 将提取的数据放入到 BeanDefinitionBuilder中，等完成所有bean的解析后统一注册到 BeanFactory
             */
            if (StringUtils.hasText(id)) {
                bean.addPropertyValue("id", id);
            }
            if (StringUtils.hasText(name)) {
                bean.addPropertyValue("name", name);
            }
            if (StringUtils.hasText(value)) {
                bean.addPropertyValue("value", value);
            }
        }
    }

# 4、创建Handler #

扩展 NamespaceHandlerSupport，目的是将自定义标签标注的类注册到 Spring 容器。

package thinking.in.spring.boot.samples.spring5.customlabel;
    
    import org.springframework.beans.factory.xml.NamespaceHandlerSupport;
    
    public class CustomLabelNamespaceHandler extends NamespaceHandlerSupport{
        @Override
        public void init() {
            // 一个标签对应一个解析器
            registerBeanDefinitionParser("mybean", new CustomLabelBeanDefinitionParser());
            registerBeanDefinitionParser("tag2", new CustomLabelBeanDefinitionParser());
        }
    }

# 5、编写 spring.handlers 和 spring.schemas文件 #

文件创建在 resources/META-INF/ 目录下。

## spring.handlers ##

文件内容如下

http\://www.rh.com/schema/customLabel=thinking.in.spring.boot.samples.spring5.customlabel.CustomLabelNamespaceHandler

## spring.schemas ##

文件内容如下

http\://www.rh.com/schema/customLabel.xsd=META-INF/spring-custom.xsd

# 6、引入自定义标签 #

引入自定义标签到Spring配置文件，配置文件如下

<?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:customLabel="http://www.rh.com/schema/customLabel"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.rh.com/schema/customLabel
            http://www.rh.com/schema/customLabel.xsd">
    
        
            
            
        
    
        <customLabel:mybean id="rh" name="rh" value="自定义标签一" />
        <customLabel:tag2 id="tag2" name="tag2" value="自定义标签2" />
    </beans>

# 7、验证 #

创建Spring引导类，测试自定义标签是否配置成功

XmlBeanFactoryBootstrap 引导类如下

package thinking.in.spring.boot.samples.spring5.bootstrap;
    
    import org.springframework.beans.factory.support.DefaultListableBeanFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    import thinking.in.spring.boot.samples.spring5.customlabel.CustomLabel;
    import thinking.in.spring.boot.samples.spring5.bean.User;
    
    public class XmlBeanFactoryBootstrap {
    
        public static void main(String[] args) {
            DefaultListableBeanFactory defaultListableBeanFactory = new XmlBeanFactory(new ClassPathResource("application-context.xml"));
    //        User user = defaultListableBeanFactory.getBean(User.class);
    //        System.out.println(user);
    
            CustomLabel customLabel = (CustomLabel) defaultListableBeanFactory.getBean("rh");
            System.out.println(customLabel.getName() + " == " + customLabel.getValue());
            CustomLabel tag2 = (CustomLabel) defaultListableBeanFactory.getBean("tag2");
            System.out.println(tag2.getName() + " == " + tag2.getValue());
        }
    }

运行结果

三月 23, 2020 2:28:29 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    信息: Loading XML bean definitions from class path resource [application-context.xml]
    rh == 自定义标签一
    tag2 == 自定义标签2