https://github.com/spring-projects/spring-framework: Spring Beans (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed 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.springframework.beans.factory.xml;

import org.w3c.dom.Attr;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;

import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.core.Conventions;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;


Convenient base class for when there exists a one-to-one mapping between attribute names on the element that is to be parsed and the property names on the Class being configured. 
Extend this parser class when you want to create a single bean definition from a relatively simple custom XML element. The resulting BeanDefinition will be automatically registered with the relevant BeanDefinitionRegistry. 
An example will hopefully make the use of this particular parser
class immediately clear. Consider the following class definition:

public class SimpleCache implements Cache {
    public void setName(String name) {...}
    public void setTimeout(int timeout) {...}
    public void setEvictionPolicy(EvictionPolicy policy) {...}
    // remaining class definition elided for clarity...
}


Then let us assume the following XML tag has been defined to
permit the easy configuration of instances of the above class;

<caching:cache name="..." timeout="..." eviction-policy="..."/>


All that is required of the Java developer tasked with writing the parser to parse the above XML tag into an actual SimpleCache bean definition is the following: 
public class SimpleCacheBeanDefinitionParser extends AbstractSimpleBeanDefinitionParser {
    protected Class getBeanClass(Element element) {
        return SimpleCache.class;
    }
}


Please note that the AbstractSimpleBeanDefinitionParser is limited to populating the created bean definition with property values. if you want to parse constructor arguments and nested elements from the supplied XML element, then you will have to implement the postProcess(BeanDefinitionBuilder, Element) method and do such parsing yourself, or (more likely) subclass the AbstractSingleBeanDefinitionParser or AbstractBeanDefinitionParser classes directly. 
The process of actually registering the SimpleCacheBeanDefinitionParser with the Spring XML parsing infrastructure is described in the Spring Framework reference documentation (in one of the appendices). 
For an example of this parser in action (so to speak), do look at the source code for the PropertiesBeanDefinitionParser; the observant (and even not so observant) reader will immediately notice that there is next to no code in the implementation. The PropertiesBeanDefinitionParser populates a PropertiesFactoryBean from an XML element that looks like this: 
<util:properties location="jdbc.properties"/>


The observant reader will notice that the sole attribute on the <util:properties/> element matches the PropertiesLoaderSupport.setLocation(Resource) method name on the PropertiesFactoryBean (the general usage thus illustrated holds true for any number of attributes). All that the PropertiesBeanDefinitionParser needs actually do is supply an implementation of the AbstractSingleBeanDefinitionParser.getBeanClass(Element) method to return the PropertiesFactoryBean type. 
Author:Rob Harrop, Rick Evans, Juergen Hoeller
See Also:
Since:2.0
/**
 * Convenient base class for when there exists a one-to-one mapping
 * between attribute names on the element that is to be parsed and
 * the property names on the {@link Class} being configured.
 *
 * <p>Extend this parser class when you want to create a single
 * bean definition from a relatively simple custom XML element. The
 * resulting {@code BeanDefinition} will be automatically
 * registered with the relevant
 * {@link org.springframework.beans.factory.support.BeanDefinitionRegistry}.
 *
 * <p>An example will hopefully make the use of this particular parser
 * class immediately clear. Consider the following class definition:
 *
 * <pre class="code">public class SimpleCache implements Cache {
 *
 *     public void setName(String name) {...}
 *     public void setTimeout(int timeout) {...}
 *     public void setEvictionPolicy(EvictionPolicy policy) {...}
 *
 *     // remaining class definition elided for clarity...
 * }</pre>
 *
 * <p>Then let us assume the following XML tag has been defined to
 * permit the easy configuration of instances of the above class;
 *
 * <pre class="code">&lt;caching:cache name="..." timeout="..." eviction-policy="..."/&gt;</pre>
 *
 * <p>All that is required of the Java developer tasked with writing
 * the parser to parse the above XML tag into an actual
 * {@code SimpleCache} bean definition is the following:
 *
 * <pre class="code">public class SimpleCacheBeanDefinitionParser extends AbstractSimpleBeanDefinitionParser {
 *
 *     protected Class getBeanClass(Element element) {
 *         return SimpleCache.class;
 *     }
 * }</pre>
 *
 * <p>Please note that the {@code AbstractSimpleBeanDefinitionParser}
 * is limited to populating the created bean definition with property values.
 * if you want to parse constructor arguments and nested elements from the
 * supplied XML element, then you will have to implement the
 * {@link #postProcess(org.springframework.beans.factory.support.BeanDefinitionBuilder, org.w3c.dom.Element)}
 * method and do such parsing yourself, or (more likely) subclass the
 * {@link AbstractSingleBeanDefinitionParser} or {@link AbstractBeanDefinitionParser}
 * classes directly.
 *
 * <p>The process of actually registering the
 * {@code SimpleCacheBeanDefinitionParser} with the Spring XML parsing
 * infrastructure is described in the Spring Framework reference documentation
 * (in one of the appendices).
 *
 * <p>For an example of this parser in action (so to speak), do look at
 * the source code for the
 * {@link org.springframework.beans.factory.xml.UtilNamespaceHandler.PropertiesBeanDefinitionParser};
 * the observant (and even not so observant) reader will immediately notice that
 * there is next to no code in the implementation. The
 * {@code PropertiesBeanDefinitionParser} populates a
 * {@link org.springframework.beans.factory.config.PropertiesFactoryBean}
 * from an XML element that looks like this:
 *
 * <pre class="code">&lt;util:properties location="jdbc.properties"/&gt;</pre>
 *
 * <p>The observant reader will notice that the sole attribute on the
 * {@code <util:properties/>} element matches the
 * {@link org.springframework.beans.factory.config.PropertiesFactoryBean#setLocation(org.springframework.core.io.Resource)}
 * method name on the {@code PropertiesFactoryBean} (the general
 * usage thus illustrated holds true for any number of attributes).
 * All that the {@code PropertiesBeanDefinitionParser} needs
 * actually do is supply an implementation of the
 * {@link #getBeanClass(org.w3c.dom.Element)} method to return the
 * {@code PropertiesFactoryBean} type.
 *
 * @author Rob Harrop
 * @author Rick Evans
 * @author Juergen Hoeller
 * @since 2.0
 * @see Conventions#attributeNameToPropertyName(String)
 */
public abstract class AbstractSimpleBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {

	
Parse the supplied Element and populate the supplied BeanDefinitionBuilder as required. 
This implementation maps any attributes present on the supplied element to PropertyValue instances, and adds them to the builder. 
The extractPropertyName(String) method is used to reconcile the name of an attribute with the name of a JavaBean property. 
Params:
  • element – the XML element being parsed
  • builder – used to define the BeanDefinition
See Also:
/**
	 * Parse the supplied {@link Element} and populate the supplied
	 * {@link BeanDefinitionBuilder} as required.
	 * <p>This implementation maps any attributes present on the
	 * supplied element to {@link org.springframework.beans.PropertyValue}
	 * instances, and
	 * {@link BeanDefinitionBuilder#addPropertyValue(String, Object) adds them}
	 * to the
	 * {@link org.springframework.beans.factory.config.BeanDefinition builder}.
	 * <p>The {@link #extractPropertyName(String)} method is used to
	 * reconcile the name of an attribute with the name of a JavaBean
	 * property.
	 * @param element the XML element being parsed
	 * @param builder used to define the {@code BeanDefinition}
	 * @see #extractPropertyName(String)
	 */
	@Override
	protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
		NamedNodeMap attributes = element.getAttributes();
		for (int x = 0; x < attributes.getLength(); x++) {
			Attr attribute = (Attr) attributes.item(x);
			if (isEligibleAttribute(attribute, parserContext)) {
				String propertyName = extractPropertyName(attribute.getLocalName());
				Assert.state(StringUtils.hasText(propertyName),
						"Illegal property name returned from 'extractPropertyName(String)': cannot be null or empty.");
				builder.addPropertyValue(propertyName, attribute.getValue());
			}
		}
		postProcess(builder, element);
	}

	
Determine whether the given attribute is eligible for being
turned into a corresponding bean property value.

The default implementation considers any attribute as eligible,
except for the "id" attribute and namespace declaration attributes.

Params:
  • attribute – the XML attribute to check
  • parserContext – the ParserContext
See Also:
/**
	 * Determine whether the given attribute is eligible for being
	 * turned into a corresponding bean property value.
	 * <p>The default implementation considers any attribute as eligible,
	 * except for the "id" attribute and namespace declaration attributes.
	 * @param attribute the XML attribute to check
	 * @param parserContext the {@code ParserContext}
	 * @see #isEligibleAttribute(String)
	 */
	protected boolean isEligibleAttribute(Attr attribute, ParserContext parserContext) {
		String fullName = attribute.getName();
		return (!fullName.equals("xmlns") && !fullName.startsWith("xmlns:") &&
				isEligibleAttribute(parserContext.getDelegate().getLocalName(attribute)));
	}

	
Determine whether the given attribute is eligible for being
turned into a corresponding bean property value.

The default implementation considers any attribute as eligible,
except for the "id" attribute.

Params:
  • attributeName – the attribute name taken straight from the XML element being parsed (never null)
/**
	 * Determine whether the given attribute is eligible for being
	 * turned into a corresponding bean property value.
	 * <p>The default implementation considers any attribute as eligible,
	 * except for the "id" attribute.
	 * @param attributeName the attribute name taken straight from the
	 * XML element being parsed (never {@code null})
	 */
	protected boolean isEligibleAttribute(String attributeName) {
		return !ID_ATTRIBUTE.equals(attributeName);
	}

	
Extract a JavaBean property name from the supplied attribute name.

The default implementation uses the Conventions.attributeNameToPropertyName(String) method to perform the extraction. 
The name returned must obey the standard JavaBean property name conventions. For example for a class with a setter method 'setBingoHallFavourite(String)', the name returned had better be 'bingoHallFavourite' (with that exact casing). 
Params:
  • attributeName – the attribute name taken straight from the XML element being parsed (never null)
Returns:the extracted JavaBean property name (must never be null)
/**
	 * Extract a JavaBean property name from the supplied attribute name.
	 * <p>The default implementation uses the
	 * {@link Conventions#attributeNameToPropertyName(String)}
	 * method to perform the extraction.
	 * <p>The name returned must obey the standard JavaBean property name
	 * conventions. For example for a class with a setter method
	 * '{@code setBingoHallFavourite(String)}', the name returned had
	 * better be '{@code bingoHallFavourite}' (with that exact casing).
	 * @param attributeName the attribute name taken straight from the
	 * XML element being parsed (never {@code null})
	 * @return the extracted JavaBean property name (must never be {@code null})
	 */
	protected String extractPropertyName(String attributeName) {
		return Conventions.attributeNameToPropertyName(attributeName);
	}

	
Hook method that derived classes can implement to inspect/change a
bean definition after parsing is complete.

The default implementation does nothing.

Params:
  • beanDefinition – the parsed (and probably totally defined) bean definition being built
  • element – the XML element that was the source of the bean definition's metadata
/**
	 * Hook method that derived classes can implement to inspect/change a
	 * bean definition after parsing is complete.
	 * <p>The default implementation does nothing.
	 * @param beanDefinition the parsed (and probably totally defined) bean definition being built
	 * @param element the XML element that was the source of the bean definition's metadata
	 */
	protected void postProcess(BeanDefinitionBuilder beanDefinition, Element element) {
	}

}