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/*
 * $Id$
 *
 * 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.struts.dispatcher;

import org.apache.struts.chain.contexts.ActionContext;

/**
 * This abstract class is a template for choosing the target method that is
 * identified by a submission parameter.
 *
 * @version $Rev$
 * @since Struts 1.4
 */
public abstract class AbstractParameterDispatcher extends AbstractDispatcher {

    /**
     * The default parameter name if no parameter is set.
     *
     * @see #getDefaultParameterName()
     */
    protected static final String DEFAULT_PARAMETER_NAME = "method";

    /**
     * Constructs a new dispatcher with the specified method resolver.
     *
     * @param methodResolver the method resolver
     */
    public AbstractParameterDispatcher(MethodResolver methodResolver) {
        super(methodResolver);
    }

    /**
     * Retrieves the name of the parameter to fallback upon if the action
     * configuration did not set the parameter attribute. The
     * default implementation returns {@link #DEFAULT_PARAMETER_NAME}.
     *
     * @return the fallback parameter name; can be null
     * @see #DEFAULT_PARAMETER_NAME
     * @see #getParameter(ActionContext)
     */
    protected String getDefaultParameterName() {
        return DEFAULT_PARAMETER_NAME;
    }

    /**
     * Retrieves the parameter name whose value will identity the intended
     * method to dispatch. The value is not necessarily a method name, but a key
     * that can resolve to one. The default implementation returns the mapping's
     * parameter attribute; otherwise fallback to the default
     * parameter name.
     *
     * @param context the current action context
     * @return the mapping's parameter name
     * @see #getDefaultParameterName()
     */
    protected String getParameter(ActionContext context) {
        String parameter = context.getActionConfig().getParameter();
        if ((parameter != null) && (parameter.trim().length() > 0)) {
            return parameter;
        }
        return getDefaultParameterName();
    }

    protected final String resolveMethodName(ActionContext context) {
        String parameter = getParameter(context);
        if ("".equals(parameter)) {
            parameter = null;
        }

        if (parameter != null) {
            return resolveParameterValue(context, parameter);
        }

        return null;
    }

    /**
     * Extracts the value that is keyed by the specified parameter.
     *
     * @param context the current action context
     * @param parameter the parameter name
     * @return the parameter value
     */
    protected abstract String resolveParameterValue(ActionContext context, String parameter);

}