elbasetag.java

ActionServlet源码 struts的一个步骤都有 知道本来有视频的太大了 就没有上传了

/*
 * $Id: ELBaseTag.java 471754 2006-11-06 14:55:09Z husted $
 *
 * 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.strutsel.taglib.html;

import org.apache.struts.taglib.html.BaseTag;
import org.apache.strutsel.taglib.utils.EvalHelper;

import javax.servlet.jsp.JspException;

/**
 * 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: 471754 $
 */
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;

    /**
     * Instance variable mapped to "ref" tag attribute. (Mapping set in
     * associated BeanInfo class.)
     */
    private String refExpr;

    /**
     * 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);
    }

    /**
     * Getter method for "ref" tag attribute. (Mapping set in associated
     * BeanInfo class.)
     */
    public String getRefExpr() {
        return (refExpr);
    }

    /**
     * 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;
    }

    /**
     * Setter method for "ref" tag attribute. (Mapping set in associated
     * BeanInfo class.)
     */
    public void setRefExpr(String refExpr) {
        this.refExpr = refExpr;
    }

    /**
     * Resets attribute values for tag reuse.
     */
    public void release() {
        super.release();
        setTargetExpr(null);
        setServerExpr(null);
        setRefExpr(null);
    }

    /**
     * Process the start tag.
     *
     * @throws 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.
     *
     * @throws 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);
        }

        if ((string =
                EvalHelper.evalString("ref", getRefExpr(), this, pageContext)) != null) {
            setRef(string);
        }
    }
}