1. 🧹 Mixing Java Code with HTML = Messy and Hard to Maintain

When you write Java code directly inside JSP (inside <% ... %> blocks),
you mix two completely different concerns:

• Presentation (HTML)
• Business logic (Java code)

Result:

• Pages become hard to read.
• Harder to debug.
• Harder to update (especially when designers and developers work together).

✅ It’s much cleaner if JSP handles only the view and Java code stays in servlets, services, or controllers.

2. 🛠️ Difficult to Reuse Logic

When Java logic is buried inside a JSP scriptlet, you cannot reuse it elsewhere.

• You cannot easily call it from other pages or controllers.
• You must copy-paste logic if you want it in another place.

✅ Moving logic to Java classes or Beans promotes code reuse.

3. 🔒 Security and Robustness Problems

Badly written scriptlets can:

• Accidentally expose sensitive server information.
• Cause runtime exceptions that break the page if not handled carefully.
• Be harder to test (because they are mixed with presentation).

✅ Separating Java code into servlets/services allows better error handling and security.

4. 🛠️ Poor MVC Architecture

Modern web applications follow MVC (Model-View-Controller) design:

Layer	Role	Where Logic Should Go
Model	Business logic, Data	Java classes (services, beans)
View	Presentation (UI)	JSP (only displaying data)
Controller	Request/Response Handling	Servlet, Controller classes

If you write Java code in JSP directly:

• You break MVC.
• View starts doing Model or Controller work.

✅ Proper separation leads to better maintainability and scaling.

5. 🚀 Modern Alternatives Exist

Today you can use:

• Expression Language (EL) ${user.name} — clean and simple
• JSTL (JSP Standard Tag Library) — for loops, conditions, etc.
• Custom tags — for reusable blocks
• Frameworks like Spring MVC — for full separation.

✅ These are designed to replace scriptlets and create clean, maintainable code.

🔥 Example: Bad (Using Scriptlet)

<%
    String name = (String) session.getAttribute("userName");
    if (name != null) {
%>
    <h1>Hello, <%= name %>!</h1>
<%
    }
%>

✅ Example: Good (Using JSTL + EL)

<c:if test="${not empty sessionScope.userName}">
    <h1>Hello, ${sessionScope.userName}!</h1>
</c:if>

No Java code inside JSP.

Easy for developers and designers to understand.

🎯 Final Summary

Problem with Scriptlets	Why It Matters
Mixing Java and HTML	Hard to read and maintain
Logic duplication	Poor code reuse
Difficult testing and security	Higher risk of bugs and leaks
Breaks MVC architecture	Makes apps harder to scale and update
Modern alternatives exist	Cleaner, safer, more maintainable code

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📢 In short:

✅ Avoid scriptlets.
✅ Use EL + JSTL.
✅ Keep Java code in Servlets, Services, or Controllers.