Spring自定义标签

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一、标签解析原理：

1、Spring通过XML解析程序将其解析为DOM树，

2、通过NamespaceHandler指定对应的Namespace的BeanDefinitionParser将其转换成BeanDefinition。

3、再通过Spring自身的功能对BeanDefinition实例化对象。

二、自定义标签步骤

1、定义三个文件

META-INF/soring.handlers 指定命名空间解析实现类

META-INF/spring.schemas 指定命名空间文件

META-INF/xxx.xsd 定义命名空间

2、实现NameSpace(命名空间)解析类（继承NamespaceHandlerSupport）

3、配置相应element元素的Parser（实现BeanDefinitionParser接口）和Bean（例如实现InitializingBean, DisposableBean，ApplicationContextAware, ApplicationListener，要看配置在element需要哪些属性）

三、应用案例

以dubbo框架为例，可以看到：

1、3个属性文件

META-INF/spring.handlers

http\://www.newlandframework.com/dubbo=com.newlandframework.rpc.spring.DubboNamespaceHandler

META-INF/spring.schemas

http\://www.newlandframework.com/dubbo/dubbo.xsd=META-INF/dubbo.xsd

dubbo.xsd

<?xml version="1.0" encoding="UTF-8"?>

<xsd:schema xmlns="http://www.newlandframework.com/dubbo"

            xmlns:xsd="http://www.w3.org/2001/XMLSchema"

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

            targetNamespace="http://www.newlandframework.com/dubbo"

            elementFormDefault="qualified"

            attributeFormDefault="unqualified">

    <xsd:import namespace="http://www.springframework.org/schema/beans"/>

    <xsd:element name="service">

        <xsd:complexType>

            <xsd:complexContent>

                <xsd:extension base="beans:identifiedType">

                    <xsd:attribute name="interfaceName" type="xsd:string" use="required"/>

                    <xsd:attribute name="ref" type="xsd:string" use="required"/>

                </xsd:extension>

            </xsd:complexContent>

        </xsd:complexType>

    </xsd:element>

    <xsd:element name="registry">

        <xsd:complexType>

            <xsd:complexContent>

                <xsd:extension base="beans:identifiedType">

                    <xsd:attribute name="ipAddr" type="xsd:string" use="required"/>

                    <xsd:attribute name="protocol" type="xsd:string" use="required"/>

                </xsd:extension>

            </xsd:complexContent>

        </xsd:complexType>

    </xsd:element>

    <xsd:element name="reference">

        <xsd:complexType>

            <xsd:complexContent>

                <xsd:extension base="beans:identifiedType">

                    <xsd:attribute name="interfaceName" type="xsd:string" use="required"/>

                    <xsd:attribute name="ipAddr" type="xsd:string" use="required"/>

                    <xsd:attribute name="protocol" type="xsd:string" use="required"/>

                </xsd:extension>

            </xsd:complexContent>

        </xsd:complexType>

    </xsd:element>

</xsd:schema>

2、Handler解析类

DubboNamespaceHandler

/*

 * 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 com.alibaba.dubbo.config.spring.schema;

import com.alibaba.dubbo.common.Version;

import com.alibaba.dubbo.config.*;

import com.alibaba.dubbo.config.spring.AnnotationBean;

import com.alibaba.dubbo.config.spring.ReferenceBean;

import com.alibaba.dubbo.config.spring.ServiceBean;

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

/**

 * DubboNamespaceHandler

 *

 * @export

 */

public class DubboNamespaceHandler extends NamespaceHandlerSupport {

    static {

        Version.checkDuplicate(DubboNamespaceHandler.class);

    }

    public void init() {

        registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));

        registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));

        registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));

        registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));

        registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));

        registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));

        registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));

        registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));

        registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));

        registerBeanDefinitionParser("annotation", new DubboBeanDefinitionParser(AnnotationBean.class, true));

    }

}

3、定义parser解析bean文件

/*

 * 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 com.alibaba.dubbo.config.spring.schema;

import com.alibaba.dubbo.common.Constants;

import com.alibaba.dubbo.common.extension.ExtensionLoader;

import com.alibaba.dubbo.common.logger.Logger;

import com.alibaba.dubbo.common.logger.LoggerFactory;

import com.alibaba.dubbo.common.utils.ReflectUtils;

import com.alibaba.dubbo.common.utils.StringUtils;

import com.alibaba.dubbo.config.*;

import com.alibaba.dubbo.config.spring.ReferenceBean;

import com.alibaba.dubbo.config.spring.ServiceBean;

import com.alibaba.dubbo.rpc.Protocol;

import org.springframework.beans.PropertyValue;

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.config.BeanDefinitionHolder;

import org.springframework.beans.factory.config.RuntimeBeanReference;

import org.springframework.beans.factory.config.TypedStringValue;

import org.springframework.beans.factory.support.ManagedList;

import org.springframework.beans.factory.support.ManagedMap;

import org.springframework.beans.factory.support.RootBeanDefinition;

import org.springframework.beans.factory.xml.BeanDefinitionParser;

import org.springframework.beans.factory.xml.ParserContext;

import org.w3c.dom.Element;

import org.w3c.dom.NamedNodeMap;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.util.Date;

import java.util.HashSet;

import java.util.Set;

import java.util.regex.Pattern;

/**

 * AbstractBeanDefinitionParser

 *

 * @export

 */

public class DubboBeanDefinitionParser implements BeanDefinitionParser {

    private static final Logger logger = LoggerFactory.getLogger(DubboBeanDefinitionParser.class);

    private static final Pattern GROUP_AND_VERION = Pattern.compile("^[\\-.0-9_a-zA-Z]+(\\:[\\-.0-9_a-zA-Z]+)?$");

    private final Class<?> beanClass;

    private final boolean required;

    public DubboBeanDefinitionParser(Class<?> beanClass, boolean required) {

        this.beanClass = beanClass;

        this.required = required;

    }

    ......

}