core/src/main/java/org/apache/commons/digester3/substitution/VariableAttributes.java

package org.apache.commons.digester3.substitution;

/*
 * 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.
 */

import org.xml.sax.Attributes;

import java.util.ArrayList;

/**
 * Wrapper for an {@link Attributes} object which expands any "variables" referenced in the attribute value via
 * ${foo} or similar. This is only done when something actually asks for the attribute value, thereby imposing no
 * performance penalty if the attribute is not used.
 * 
 * @since 1.6
 */
public class VariableAttributes
    implements Attributes
{

    // list of mapped attributes.
    private final ArrayList<String> values = new ArrayList<String>( 10 );

    private Attributes attrs;

    private VariableExpander expander;

    // ------------------- Public Methods

    /**
     * Specify which attributes class this object is a proxy for.
     *
     * @param attrs The attributes where variables have to be expanded.
     * @param expander The variables expander instance.
     */
    public void init( Attributes attrs, VariableExpander expander )
    {
        this.attrs = attrs;
        this.expander = expander;

        // I hope this doesn't release the memory for this array; for
        // efficiency, this should just mark the array as being size 0.
        values.clear();
    }

    /**
     * {@inheritDoc}
     */
    public String getValue( int index )
    {
        if ( index >= values.size() )
        {
            // Expand the values array with null elements, so the later
            // call to set(index, s) works ok.
            //
            // Unfortunately, there is no easy way to set the size of
            // an arraylist; we must repeatedly add null elements to it..
            values.ensureCapacity( index + 1 );
            for ( int i = values.size(); i <= index; ++i )
            {
                values.add( null );
            }
        }

        String s = values.get( index );

        if ( s == null )
        {
            // we have never been asked for this value before.
            // get the real attribute value and perform substitution
            // on it.
            s = attrs.getValue( index );
            if ( s != null )
            {
                s = expander.expand( s );
                values.set( index, s );
            }
        }

        return s;
    }

    /**
     * {@inheritDoc}
     */
    public String getValue( String qname )
    {
        int index = attrs.getIndex( qname );
        if ( index == -1 )
        {
            return null;
        }
        return getValue( index );
    }

    /**
     * {@inheritDoc}
     */
    public String getValue( String uri, String localname )
    {
        int index = attrs.getIndex( uri, localname );
        if ( index == -1 )
        {
            return null;
        }
        return getValue( index );
    }

    // plain proxy methods follow : nothing interesting :-)
    /**
     * {@inheritDoc}
     */
    public int getIndex( String qname )
    {
        return attrs.getIndex( qname );
    }

    /**
     * {@inheritDoc}
     */
    public int getIndex( String uri, String localpart )
    {
        return attrs.getIndex( uri, localpart );
    }

    /**
     * {@inheritDoc}
     */
    public int getLength()
    {
        return attrs.getLength();
    }

    /**
     * {@inheritDoc}
     */
    public String getLocalName( int index )
    {
        return attrs.getLocalName( index );
    }

    /**
     * {@inheritDoc}
     */
    public String getQName( int index )
    {
        return attrs.getQName( index );
    }

    /**
     * {@inheritDoc}
     */
    public String getType( int index )
    {
        return attrs.getType( index );
    }

    /**
     * {@inheritDoc}
     */
    public String getType( String qname )
    {
        return attrs.getType( qname );
    }

    /**
     * {@inheritDoc}
     */
    public String getType( String uri, String localname )
    {
        return attrs.getType( uri, localname );
    }

    /**
     * {@inheritDoc}
     */
    public String getURI( int index )
    {
        return attrs.getURI( index );
    }

}