基于Extensible XML authoring 擴充Spring XML元素

本篇我們一起來看一下基于Extensible XML authoring 擴充Spring XML元素。這裡我總結了以下内容：

* Spring XML 擴充
	* 編寫 XML Schema 檔案:定義 XML 結構
	* 自定義 NamespaceHandler 實作:命名空間綁定
	* 自定義 BeanDefinitionParser 實作:XML 元素與 BeanDefinition 解析
	* 注冊 XML 擴充:命名空間與 XML Schema 映射           

接下來我們就通過實際案例的方式一起實踐一下。代碼如下：

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

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

    <!-- 定義 User 類型（複雜類型） -->
    <xsd:complexType name="User">
        <xsd:attribute name="id" type="xsd:long" use="required"/>
        <xsd:attribute name="name" type="xsd:string" use="required"/>
        <xsd:attribute name="city" type="City"/>
    </xsd:complexType>

    <!-- 定義 City 類型（簡單類型，枚舉） -->
    <xsd:simpleType name="City">
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="BEIJING"/>
            <xsd:enumeration value="HANGZHOU"/>
            <xsd:enumeration value="SHANGHAI"/>
        </xsd:restriction>
    </xsd:simpleType>

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


## 定義 namespace 與 NamespaceHandler 的映射
http\://time.eleven.org/schema/users=org.eleven.thinking.in.spring.configuration.metadata.UsersNamespaceHandler


http\://time.eleven.org/schema/users.xsd = org/eleven/thinking/in/spring/configuration/metadata/users.xsd


/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.eleven.thinking.in.spring.configuration.metadata;

import org.springframework.beans.factory.xml.NamespaceHandler;
import org.springframework.beans.factory.xml.NamespaceHandlerSupport;

/**
 * "users.xsd" {@link NamespaceHandler} 實作
 *
 * @author <a href="mailto:[email protected]">eleven</a>
 * @since
 */
public class UsersNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        // 将 "user" 元素注冊對應的 BeanDefinitionParser 實作
        registerBeanDefinitionParser("user", new UserBeanDefinitionParser());
    }
}


/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.eleven.thinking.in.spring.configuration.metadata;

import org.eleven.thinking.in.spring.ioc.overview.domain.User;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser;
import org.springframework.beans.factory.xml.BeanDefinitionParser;
import org.springframework.beans.factory.xml.ParserContext;
import org.springframework.util.StringUtils;
import org.w3c.dom.Element;

/**
 * "user" 元素的 {@link BeanDefinitionParser} 實作
 *
 * @author <a href="mailto:[email protected]">eleven</a>
 * @since
 */
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);
        setPropertyValue("city", element, builder);
    }

    private void setPropertyValue(String attributeName, Element element, BeanDefinitionBuilder builder) {
        String attributeValue = element.getAttribute(attributeName);
        if (StringUtils.hasText(attributeValue)) {
            builder.addPropertyValue(attributeName, attributeValue); // -> <property name="" value=""/>

        }
    }
}