abstracttag.java

OS(OpenSymphony)的SiteMesh是一个用来在JSP中实现页面布局和装饰（layout and decoration）的框架组件

/*
 * Title:        AbstractTag
 * Description:
 *
 * This software is published under the terms of the OpenSymphony Software
 * License version 1.1, of which a copy has been included with this
 * distribution in the LICENSE.txt file.
 */

package com.opensymphony.module.sitemesh.taglib;

import com.opensymphony.module.sitemesh.Page;
import com.opensymphony.module.sitemesh.RequestConstants;
import com.opensymphony.module.sitemesh.util.OutputConverter;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.jsp.tagext.BodyTagSupport;
import java.io.Writer;

/**
 * Convenience implementation of Tag containing generice methods required
 * by all (or most) taglibs.
 *
 * @author <a href="mailto:[e-mail]">Joe Walnes</a>
 * @version $Revision: 1.4 $
 */
public abstract class AbstractTag extends BodyTagSupport implements RequestConstants {
    protected PageContext pageContext;
    protected Tag parent;

    /** To be implemented by all empty tags. */
    public abstract int doEndTag() throws JspException;

    /** Returns SKIP_BODY. */
    public int doStartTag() {
        return SKIP_BODY;
    }

    public void release() {
    }

    public Tag getParent() {
        return parent;
    }

    public void setParent(Tag parent) {
        this.parent = parent;
    }

    public void setPageContext(PageContext pageContext) {
        this.pageContext = pageContext;
    }

    /**
     * Return the Page object from the PAGE scope. If this is found in REQUEST scope
     * instead, it will be moved into PAGE scope - to handle multi-level includes.
     */
    protected Page getPage() {
        Page p = (Page)pageContext.getAttribute(PAGE, PageContext.PAGE_SCOPE);

        if (p == null) {
            p = (Page)pageContext.getAttribute(PAGE, PageContext.REQUEST_SCOPE);
            if (p == null) {
                pageContext.removeAttribute(PAGE, PageContext.PAGE_SCOPE);
            }
            else {
                pageContext.setAttribute(PAGE, p, PageContext.PAGE_SCOPE);
            }
            pageContext.removeAttribute(PAGE, PageContext.REQUEST_SCOPE);
        }
        return p;
    }

    /** Log exception generated by taglib. */
    protected static void trace(Exception e) {
        e.printStackTrace();
    }

    /**
     * Get the outputWriter.  This method should be used in preference to
     * <code>pageContext.getOut()</code>, as some charset conversions may need
     * to happen in some servers.
     * @return the writer for use in the tag
     */
    protected Writer getOut() {
        return OutputConverter.getWriter(pageContext.getOut());
    }
}