/*
 * $Id: ELMessagesPresentTag.java 54933 2004-10-16 17:04:52Z germuska $ 
 *
 * Copyright 1999-2004 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.strutsel.taglib.logic;

import org.apache.struts.taglib.logic.MessagesPresentTag;
import javax.servlet.jsp.JspException;
import org.apache.strutsel.taglib.utils.EvalHelper;

/**
 * Evalute to <code>true</code> if an <code>ActionMessages</code> class or a
 * class that can be converted to an <code>ActionMessages</code> class is in
 * request scope under the specified key and there is at least one message in
 * the class or for the property specified.
 *<p>
 * This class is a subclass of the class
 * <code>org.apache.struts.taglib.logic.MessagesPresentTag</code> which
 * provides most of the described functionality.  This subclass allows all
 * attribute values to be specified as expressions utilizing the JavaServer
 * Pages Standard Library expression language.
 *
 * @version $Rev: 54933 $
 */
public class ELMessagesPresentTag extends MessagesPresentTag {

    /**
     * Instance variable mapped to "name" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    private String nameExpr;
    /**
     * Instance variable mapped to "property" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    private String propertyExpr;
    /**
     * Instance variable mapped to "message" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    private String messageExpr;

    /**
     * Getter method for "name" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public String getNameExpr() { return (nameExpr); }
    /**
     * Getter method for "property" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public String getPropertyExpr() { return (propertyExpr); }
    /**
     * Getter method for "message" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public String getMessageExpr() { return (messageExpr); }

    /**
     * Setter method for "name" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public void setNameExpr(String nameExpr) { this.nameExpr = nameExpr; }
    /**
     * Setter method for "property" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public void setPropertyExpr(String propertyExpr) { this.propertyExpr = propertyExpr; }
    /**
     * Setter method for "message" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public void setMessageExpr(String messageExpr) { this.messageExpr = messageExpr; }

    /**
     * Releases state of custom tag so this instance can be reused.
     */
    public void release()
    {
        super.release();
        setNameExpr(null);
        setPropertyExpr(null);
        setMessageExpr(null);
    }
    
    /**
     * Process the start tag.
     *
     * @exception JspException if a JSP exception has occurred
     */
    public int doStartTag() throws JspException {
        evaluateExpressions();
        return (super.doStartTag());
    }
    
    /**
     * Processes all attribute values which use the JSTL expression evaluation
     * engine to determine their values.
     *
     * @exception JspException if a JSP exception has occurred
     */
    private void evaluateExpressions() throws JspException {
        String  string  = null;

        if ((string = EvalHelper.evalString("name", getNameExpr(),
                                            this, pageContext)) != null)
            setName(string);

        if ((string = EvalHelper.evalString("property", getPropertyExpr(),
                                            this, pageContext)) != null)
            setProperty(string);

        if ((string = EvalHelper.evalString("message", getMessageExpr(),
                                            this, pageContext)) != null)
            setMessage(string);
    }
}