What's the difference between including files with JSP include directive, JSP include action and using JSP Tag Files?

Importance of inclusion method selection

Selecting the appropriate inclusion method is like picking the right tool. Incorrect selection impacts performance and maintainability.

• The include directive is perfect for static content as it's evaluated at compile time.
• The include action enables real-time data inclusion, making it ideal for frequently changing content.
• JSP Tag Files or custom tags provide the highest level of abstraction by encapsulating complex functions within reusable tags.

Variable scopes and content refreshes

The proper scope and update mechanism for your variables and content directly affect your application's behavior.

• With an include directive, scriptlet variables from the parent are available in the included file.
• For the include action, this is not the case as they're treated separately during parsing.
• An include action fetches updated content with each request. For an include directive, you need to recompile the parent JSP.

Best practices for performance

Understanding the performance implications of these methods is key to optimizing your application.

• While the include directive delivers quicker responses, the include action allows for more real-time output.
• To balance performance and dynamics, consider prefetching or caching strategies for include action.

Making the most out of JSTL

The JSP Standard Tag Library, or JSTL, introduces the <c:import> tag, helping you fetch content even from a remote URL, and enables manipulation by storing the result in a variable.

Real-life application examples

Here's how you might use these inclusions in a practical scenario:

• Include directive: static disclaimers in an e-commerce application.
• Include action: a personalized dashboard that changes with each user request.
• Custom tags: reusable UI components like search bars or form validation functions.

Common pitfalls and how to sidestep them

Beware of these common issues and remember to:

• Recompile your JSP after changes to included files are made when using include directive.
• Be mindful of the performance impacts of the include action - it's not always necessary to use dynamic content.
• Use custom tags sparingly to avoid excess complexity in your JSP pages.