jsp

Writing HTML in Java servlets is painful—Java code is mixed with HTML strings. Web designers who don’t know Java need to modify the look-and-feel. How can we separate presentation from business logic?

JSP (JavaServer Pages) is similar to servlets but centered on look-and-feel. JSP scripts are HTML-like with embedded Java code, compiled into servlets. They enable non-Java staff to maintain the UI separately from business logic.

1. JSP script: HTML file with embedded Java (scriptlets, expressions, declarations, directives)
2. Lifecycle: Translation (JSP → servlet source) → Compilation (servlet source → .class) → init() → service() → destroy()
3. Directives: <%@ page %> (page settings), <%@ include %> (static includes), <%@ taglib %> (custom tags)
4. Scripting elements: <%! %> declarations, <% %> scriptlets, <%= %> expressions
5. EL (Expression Language): ${bean.property} syntax for accessing Java beans without scriptlets
6. JSTL: Standard tag library (<c:if>, <c:forEach>, <c:out>) enabling logic without Java code
7. Implicit objects: request, response, session, application, out, pageContext, config, page, exception
8. Compilation: JSP is compiled into a servlet on first access
9. Separation: UI in JSP, business logic in EJB/servlets
10. J2EE integration: Can call EJB components, use JNDI, etc.

JSP is perfect when you want physically separate, easily maintainable UI code.

• HTML-centric: Looks like HTML with embedded Java
• Compiles to servlet: Under the hood, it’s a servlet
• Lifecycle: Translation → Compilation → init → service → destroy
• Directives: page, include, taglib — control page behavior
• EL (Expression Language): ${} syntax, auto-scoped attribute lookup
• JSTL: Core, formatting, SQL, XML, functions tag libraries
• Implicit objects: 9 pre-defined objects accessible in any JSP
• No compiler needed: At deployment time
• Non-Java friendly: Web designers can maintain JSPs
• Separate maintenance: UI separated from business logic
• J2EE standard: Part of J2EE platform

• Built from: Servlets — JSP compiles to servlets
• Built from: Java Platforms — JSP is part of J2EE
• Builds into: EJB Container — JSP can call EJBs
• Related: JSP — alternative to servlets for presentation
• Contrasts with: Session Bean — JSP is presentation, EJBs are business logic

• Scriptlet pollution: Avoid too much Java in JSP (use JSTL/EL)
• First-access delay: Compilation happens on first access
• Chapter 22: See EJB with JSP examples there
• Modern alternative: Consider Facelets/Thymeleaf in modern apps