/*
 * 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 org.apache.taglibs.standard.lang.jstl;

/**
 * <p>This class is used to customize the way the evaluator resolves
 * variable references.  For example, instances of this class can
 * implement their own variable lookup mechanisms, or introduce the
 * notion of "implicit variables" which override any other variables.
 * An instance of this class should be passed to the evaluator's
 * constructor.
 * <p>Whenever the evaluator is invoked, it is passed a "context"
 * Object from the application.  For example, in a JSP environment,
 * the "context" is a PageContext.  That context object is eventually
 * passed to this class, so that this class has a context in which to
 * resolve variables.
 *
 * @author Nathan Abramson - Art Technology Group
 */
public interface VariableResolver {
    //-------------------------------------

    /**
     * Resolves the specified variable within the given context.
     * Returns null if the variable is not found.
     */
    public Object resolveVariable(String pName,
                                  Object pContext)
            throws ELException;

    //-------------------------------------
}
