Tag Attributes


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Tag Attributes

Hello Tag

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Tags become more useful once you add attributes. This example creates a ct:href tag.

With session rewriting, even browsers without cookies can support sessions. However, every <a href> needs a call to response.encodeURL(), which is annoying. With the ct:href tag, you get that for free.

Using an attribute taglib

href.jsp

<%@ taglib prefix="ct" uri="WEB-INF/tags.tld" %> Message: <ct:href href="test.jsp">test link</ct:href>

Message: <a href="test.jsp;jsessionid=1234">test link</a>

Defining the tag

The href tag has a single attribute href. Corresponding to the attribute href, the HrefTag class implements getHref() and setHref() methods.

HrefTag.java

package test;

import java.io.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

public class HrefTag extends TagSupport  {
  private String href;

  public String getHref()
  {
    return href;
  }

  public void setHref(String href)
  {
    this.href = href;
  }

  public int doStartTag() throws JspException
  {
    try {
      JspWriter out = pageContext.getOut();
      HttpServletResponse response;
      response = (HttpServletResponse) pageContext.getResponse();

      out.print("<a href=\"");
      out.print(response.encodeURL(href));
      out.print("\">");
    } catch (IOException e) {
    }
    
    return EVAL_BODY;
  }

  public int doEndTag() throws JspException
  {
    try {
      pageContext.getOut().print("</a>");
    } catch (IOException e) {
    }
    
    return EVAL_PAGE;
  }
}

Attribute Configuration

Each expected attribute needs an entry in the .tld. In this case, href is a required attribute, so the configuration needs to set required. By setting required, the JSP parser can detect errors at parse-time, making it easier to develop JSP pages with the tag library.

WEB-INF/tag.tld
<taglib> <tag> <name>href</name> <tagclass>test.HrefTag</tagclass> <attribute> <name>href</name> <required>true</required> </attribute> </tag> </taglib>

Hello Tag

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