Servlets and JSP - Java Examples in a Nutshell - page 484

Defining a Custom Tag
DecorBox.java implements a simple custom tag. The doStartTag() method is
called to output HTML text when the <decor:box> tag is encountered, and the
doEndTag() method is called to output HTML when the closing </decor:box> tag
is encountered. These methods use nested HTML tables to produce the desired
box effect. Note that the class defines setter methods for a number of String prop-
erties. These properties define the supported attributes for the tag. For example, if
a <decor:box> tag includes a margin="10" attribute, the setMargin() method is
called with the string “10” before doStartTag() is called.

Example 18−9: DecorBox.java

package com.davidflanagan.examples.servlet;
import javax.servlet.jsp.*; // JSP classes

import javax.servlet.jsp.tagext.*; // Tag Library classes

import java.io.IOException;

/**
* This Tag implementation is part of the "decor" tag library. It uses HTML
* tables to display a decorative box (with an optional title) around its
* content. The various properties correspond to the attributes supported by
* the tag.
**/
public class DecorBox extends TagSupport {
// These fields contain values that control the appearance of the box
String align; // Alignment of the box

String title; // Title for the box

String titleColor; // Title foreground color

String titleAlign; // Title alignment relative to box

String color; // Box background color

String borderColor; // Border (and title background) color

String margin; // Pixels between box edge and content

String borderWidth; // Pixel width of the box border

// The following property setter methods set the values of the fields above
// When a JSP page uses this tag any tag attribute settings will be
// translated into calls to these methods.
public void setAlign(String value) { align = value; }
public void setTitle(String value) { title = value; }
public void setTitleColor(String value) { titleColor = value; }
public void setTitleAlign(String value) { titleAlign = value; }
public void setColor(String value) { this.color = value; }
public void setBorderColor(String value) { borderColor = value; }
public void setMargin(String value) { margin = value; }
public void setBorderWidth(String value) { borderWidth = value; }

/**
* This inherited method is always the first property setter invoked
* by the JSP container. We don't care about the page context here, but
* use this method to set the default values of the various properties.
* They are initialized here in case the JSP container wants to reuse
* this Tag object on multiple pages.
**/
public void setPageContext(PageContext context) {
// Important! Let the superclass save the page context object.
// We'll need it in doStartTag() below.
super.setPageContext(context);