mappedpropertyrule.java

JAVA 文章管理系统源码

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 * 
 * 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.apache.commons.betwixt.digester;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/** <p>Factors out common code used by Betwixt rules that access bean properties.
  * Maybe a lot of this should be moved into <code>BeanUtils</code>.</p>
  *
  * @author Robert Burrell Donkin
  * @sinec 0.5
  */
public abstract class MappedPropertyRule extends RuleSupport {

    /** Logger */
    private static final Log log = LogFactory.getLog( MappedPropertyRule.class );   
     /** Classloader used to load classes by name */
    private ClassLoader classLoader;
    /** Base constructor */
    public MappedPropertyRule() {
        this.classLoader = getClass().getClassLoader();
    }
    
    

    // Implementation methods
    //-------------------------------------------------------------------------    

    /** 
     * Returns the property descriptor for the class and property name.
     * Note that some caching could be used to improve performance of 
     * this method. Or this method could be added to PropertyUtils.
     *
     * @param beanClass descriptor for property in this class
     * @param propertyName descriptor for property with this name
     * @return property descriptor for the named property in the given class 
     */
    protected PropertyDescriptor getPropertyDescriptor( Class beanClass, 
                                                        String propertyName ) {
        if ( beanClass != null && propertyName != null ) {
            if (log.isTraceEnabled()) {
                log.trace("Searching for property " + propertyName + " on " + beanClass);
            }
            try {
                BeanInfo beanInfo = Introspector.getBeanInfo( beanClass );
                PropertyDescriptor[] descriptors = 
                    beanInfo.getPropertyDescriptors();
                if ( descriptors != null ) {
                    for ( int i = 0, size = descriptors.length; i < size; i++ ) {
                        PropertyDescriptor descriptor = descriptors[i];
                        if ( propertyName.equals( descriptor.getName() ) ) {
                            log.trace("Found matching method.");
                            return descriptor;
                        }
                    }
                }
                log.trace("No match found.");
                return null;
            } catch (Exception e) {
                log.warn( "Caught introspection exception", e );
            }
        }
        return null;
    }
    
    
    /**
     * Gets the type of a property
     *
     * @param propertyClassName class name for property type (may be null)
     * @param beanClass class that has property 
     * @param propertyName the name of the property whose type is to be determined
     * @return property type 
     */
    protected Class getPropertyType( String propertyClassName, 
                                     Class beanClass, String propertyName ) {
        // XXX: should use a ClassLoader to handle 
        //      complex class loading situations
        if ( propertyClassName != null ) {
            try {
                Class answer = classLoader.loadClass(propertyClassName);
                if (answer != null) {
                    if (log.isTraceEnabled()) {
                        log.trace("Used specified type " + answer);
                    }
                    return answer;
                }
            } catch (Exception e) {
                log.warn("Cannot load specified type", e);
            }
        }
        
        PropertyDescriptor descriptor = 
            getPropertyDescriptor( beanClass, propertyName );        
        if ( descriptor != null ) { 
            return descriptor.getPropertyType();
        }
        
        if (log.isTraceEnabled()) {
            log.trace("Cannot find property type.");
            log.trace("  className=" + propertyClassName 
                        + " base=" + beanClass + " name=" + propertyName);
        }
        return null;            
    }
}