Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

348

Chapter 14 Creating Custom JSP Tag Libraries

Listing 14.26 IfElseTag.java 

package coreservlets.tags;

import javax.servlet.jsp.*;

import javax.servlet.jsp.tagext.*;

import java.io.*;

import javax.servlet.*;

/** The else part of an if tag.

 */

public class IfElseTag extends BodyTagSupport {

  public int doStartTag() throws JspTagException {

    IfTag parent =

      (IfTag)findAncestorWithClass(this, IfTag.class);

    if (parent == null) {

      throw new JspTagException("else not inside if");

    } else if (!parent.hasCondition()) {

      String warning =

        "condition tag must come before else tag";

      throw new JspTagException(warning);

    }

    return(EVAL_BODY_TAG);

  }

  public int doAfterBody() {

    IfTag parent =

      (IfTag)findAncestorWithClass(this, IfTag.class);

    if (!parent.getCondition()) {

      try {

        BodyContent body = getBodyContent();

        JspWriter out = body.getEnclosingWriter();

        out.print(body.getString());

      } catch(IOException ioe) {

        System.out.println("Error in IfElseTag: " + ioe);

      }

    }

    return(SKIP_BODY);

  }

}

The Tag Library Descriptor File

Even though there is an explicit required nesting structure for the tags just

defined, the tags must be declared separately in the TLD file. This means

that nesting validation is performed only at request time, not at page transla 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.