/*
 * $Id: ELBaseTag.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.html;

import org.apache.struts.taglib.html.BaseTag;
import javax.servlet.jsp.JspException;
import org.apache.strutsel.taglib.utils.EvalHelper;

/**
 * Renders an HTML <base> element with an href 
 * attribute pointing to the absolute location of the enclosing JSP page. This 
 * tag is only valid when nested inside a head tag body. The presence 
 * of this tag allows the browser to resolve relative URL's to images,
 * CSS stylesheets  and other resources in a manner independent of the URL
 * used to call the ActionServlet.
 *<p>
 * This class is a subclass of the class
 * <code>org.apache.struts.taglib.html.BaseTag</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 ELBaseTag extends BaseTag {

    /**
     * Instance variable mapped to "target" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    private String targetExpr;
    /**
     * Instance variable mapped to "server" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    private String serverExpr;

    /**
     * Getter method for "target" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public String getTargetExpr() { return (targetExpr); }
    /**
     * Getter method for "server" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public String getServerExpr() { return (serverExpr); }

    /**
     * Setter method for "target" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public void setTargetExpr(String targetExpr) { this.targetExpr = targetExpr; }
    /**
     * Setter method for "server" tag attribute.
     * (Mapping set in associated BeanInfo class.)
     */
    public void setServerExpr(String serverExpr) { this.serverExpr = serverExpr; }

    /**
     * Resets attribute values for tag reuse.
     */
    public void release()
    {
        super.release();
        setTargetExpr(null);
        setServerExpr(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("target", getTargetExpr(),
                                            this, pageContext)) != null)
            setTarget(string);

        if ((string = EvalHelper.evalString("server", getServerExpr(),
                                            this, pageContext)) != null)
            setServer(string);
    }
}