Replacing Embedded Java in Java Server Pages with Custom JSP Tags

Introduction

In this guide, we’ll explore how to replace embedded Java code within Java Server Pages (JSP) using custom JSP tags. If you’re a Java Developer transitioning from a different skillset or specialty, this guide will help you understand the process step by step.

Prerequisites

Before we begin, make sure you have the following prerequisites in place:

  1. Basic familiarity with Java programming.
  2. Maven installed to manage project dependencies.
  3. A code editor of your choice.
  4. Java Development Kit (JDK) installed.

1. Project Setup

Let’s start by setting up a sample project to demonstrate custom JSP tags. Follow these steps:

  1. Create a new project named “charity-custom-tags” using the Maven Web Archetype Template.
  2. Update the web.xml deployment descriptor to disable compiling of embedded Java code in JSPs by adding the line: 
    <scripting-invalid>true</scripting-invalid>
  3. Expand the Maven dependencies in your project’s pom.xml to include the Apache Commons Lang3 library: 
    <dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
    <scope>compile</scope>
</dependency>

2. Creating Custom JSP Tags

Now, let’s create a custom JSP tag called “formatDate” to format display dates based on different preferences:

  1. Define the “formatDate” tag in the nicordesigns.tld tag library definition file.
  2. Utilize the tag in a JSP page, such as dates.jsp, to display formatted dates.

3. Implementing the Custom Tag Handler

The custom tag handler, known as FormatDateTag, is the backend code responsible for processing the “formatDate” tag. It’s an implementation of the javax.servlet.jsp.tagext.TagSupport class. Here’s how it works:

  1. Override the doEndTag method to generate and display a custom formatted date.
  2. Utilize TagSupport methods to interact with the JspWriter object and write data to the response.
  3. Copy the FormatDateTag class and the nicordesigns.tld file to your main project.

4. Enhancing the Tag Library

Let’s extend the tag library by adding new functionality:

  1. Create a TimeUtils Java utility helper class to enhance tag functionality.
  2. Update the nicordesigns.tld file to include the new function.
  3. Update the necessary JSP files, like base.jspf, with the required taglib libraries.

Conclusion

By following this guide, you’ve learned how to replace embedded Java code with custom JSP tags. This approach enhances code readability, maintainability, and promotes a more organized structure for your Java web application.

For a detailed guide, refer to the official Oracle documentation on Understanding and Creating Custom JSP Tags.