Developing Simple Tag Handlers (SAP Library - Developing Applications Using Java)

Developing Simple Tag Handlers

Use

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

...

1. Create a class that extends the javax.servlet.jsp.tagext.SimpleTagSupport interface.

2. Optionally, in the class define a set of properties in a JavaBeans manner (class variables with getter and setter methods).

3. 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());

}