Developing Simple Tag Handlers

Context

You implement the functions of your simple tags in tag handler classes. A simple tag handler class implements the javax.servlet.jsp.tagext.SimpleTagSupport interface.

Procedure

Create a class that extends the javax.servlet.jsp.tagext.SimpleTagSupport interface.
Optionally, in the class define a set of properties in a JavaBeans manner (class variables with getter and setter methods).
Override the doTag() method of SimpleTagSupport defining the required behavior of your custom tag.

Example

We want to create a custom tag that generates a simple HTML table.

With this simple tag handler we use javax.servlet.jsp.JspContext , unlike with classic tag handlers, which use javax.servlet.jsp.PageContext .

getJspContext().getOut().write(tableString);

We write the body of the tag in the output. Here, the body is instance of class javax.servlet.jsp.tagext.JspFragment .

getJspBody().invoke(getJspContext().getOut());

The complete source code is the following:

package com.sap.demo.exampletags;

import java.io.IOException;
import java.text.MessageFormat;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class HelloWorldTag  extends SimpleTagSupport{

  private static final long serialVersionUID = 956562171591119686L;
  private String bgcolor;
  private String title;

  public String getBgcolor() {
    return bgcolor;
  }

  public void setBgcolor(String bgcolor) {
    this.bgcolor = bgcolor;
  }

  public String getTitle() {
    return title;
  }

  public void setTitle(String title) {
    this.title = title;
  }

  @Override
  public void doTag() throws JspException, IOException {
    try {
      String tableString = MessageFormat.format(
          "<table border=\"1\"><tr><td><b>{0}</b></td></tr><tr><td bgcolor=\"{1}\">",
          getTitle(), getBgcolor());
      getJspContext().getOut().write(tableString);
      getJspBody().invoke(getJspContext().getOut());
      getJspContext().getOut().write("</td></tr></table>");
    } catch(IOException e) {      
      throw new JspTagException("IO Error: " + e.getMessage());
    }
  }
}