src/java/org/apache/commons/jelly/impl/DynamicDynaBeanTag.java

/*
 * Copyright 2002,2004 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.jelly.impl;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.commons.beanutils.DynaClass;
import org.apache.commons.jelly.DynaBeanTagSupport;
import org.apache.commons.jelly.JellyTagException;
import org.apache.commons.jelly.MissingAttributeException;
import org.apache.commons.jelly.XMLOutput;
import org.apache.commons.jelly.expression.Expression;

/**
 * This tag is bound onto a {@link DynaClass} instance.
 * When the tag is invoked a {@link DynaBean will be created using the tags attributes.
 * So this class is like a {@link DynaBean} implemenation of {@link DynamicBeanTag}
 *
 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
 * @version $Revision: 1.7 $
 */
public class DynamicDynaBeanTag extends DynaBeanTagSupport implements BeanSource {

    /** the bean class */
    private DynaClass beanClass;

    /**
     * the tag attribute name that is used to declare the name
     * of the variable to export after running this tag
     */
    private String variableNameAttribute;

    /** the current variable name that the bean should be exported as */
    private String var;

    /** the set of attribute names we've already set */
    private Set setAttributesSet = new HashSet();

    /** the attribute definitions */
    private Map attributes;

    public DynamicDynaBeanTag(DynaClass beanClass, Map attributes, String variableNameAttribute) {
        this.beanClass = beanClass;
        this.attributes = attributes;
        this.variableNameAttribute = variableNameAttribute;
    }

    public void beforeSetAttributes() throws JellyTagException {
        // create a new dynabean before the attributes are set
        try {
            setDynaBean( beanClass.newInstance() );
        } catch (IllegalAccessException e) {
            throw new JellyTagException("Could not instantiate dynabean",e);
        } catch (InstantiationException e) {
            throw new JellyTagException("Could not instantiate dynabean",e);
        }

        setAttributesSet.clear();
    }

    public void setAttribute(String name, Object value) throws JellyTagException {
        boolean isVariableName = false;
        if (variableNameAttribute != null ) {
            if ( variableNameAttribute.equals( name ) ) {
                if (value == null) {
                    var = null;
                }
                else {
                    var = value.toString();
                }
                isVariableName = true;
            }
        }
        if (! isVariableName) {

            // #### strictly speaking we could
            // know what attributes are specified at compile time
            // so this dynamic set is unnecessary
            setAttributesSet.add(name);

            // we could maybe implement attribute specific validation here

            super.setAttribute(name, value);
        }
    }

    // Tag interface
    //-------------------------------------------------------------------------
    public void doTag(XMLOutput output) throws JellyTagException {

        // lets find any attributes that are not set and
        for ( Iterator iter = attributes.values().iterator(); iter.hasNext(); ) {
            Attribute attribute = (Attribute) iter.next();
            String name = attribute.getName();
            if ( ! setAttributesSet.contains( name ) ) {
                if ( attribute.isRequired() ) {
                    throw new MissingAttributeException(name);
                }
                // lets get the default value
                Object value = null;
                Expression expression = attribute.getDefaultValue();
                if ( expression != null ) {
                    value = expression.evaluate(context);
                }

                // only set non-null values?
                if ( value != null ) {
                    super.setAttribute(name, value);
                }
            }
        }

        invokeBody(output);

        // export the bean if required
        if ( var != null ) {
            context.setVariable(var, getDynaBean());
        }
    }

    // Properties
    //-------------------------------------------------------------------------
    /**
     * @return the bean that has just been created
     */
    public Object getBean() {
        return getDynaBean();
    }
}