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14.8 Using Nested Tags

347

Listing 14.25 IfThenTag.java 

package coreservlets.tags;

import javax.servlet.jsp.*;

import javax.servlet.jsp.tagext.*;

import java.io.*;

import javax.servlet.*;

/** The then part of an if tag.

 */

public class IfThenTag extends BodyTagSupport {

  public int doStartTag() throws JspTagException {

    IfTag parent =

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

    if (parent == null) {

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

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

      String warning =

        "condition tag must come before then 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 IfThenTag: " + ioe);

      }

    }

    return(SKIP_BODY);

  }

}

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