Avoiding Scriptlets: Cleaner Separation in Legacy Apps: JSP from a practitioner�s perspective with timeless lessons.
\n \n\n \nA late night in a JSP dungeon
\n \n\n \nLast night I was chasing a NullPointer on a page that looked innocent. A single JSP with a few scriptlets tucked between table cells and an if that tried to be clever. A tiny change to a bean broke a branch and the page threw an exception right in the face of the user. Logs were no help. We had business rules mixed into HTML with a dash of JDBC and a sprinkle of date math. When a page looks like a sandwich of Java and markup, you cannot tell where the error really lives. It is not the worst code I have seen, but it is the kind that steals your weekend. This post is that reminder I wish someone had printed and taped to the monitor above that machine: avoid scriptlets and keep a clean separation even in old apps.
\n \n\n \nWhy scriptlets keep biting
\n \n\n \nScriptlets felt handy when we were all rushing pages out the door. A quick for right in the JSP and you are done. The problem is you pay later. Scriptlets mix control flow with markup, so every tiny feature grows hidden paths and side effects right where designers need to change copy and structure. You cannot unit test a JSP with scriptlets in any sane way, and your code editor treats those blocks like strangers. The template becomes a maze of opening braces and closing braces, making maintenance slow and scary. I have seen teams try to fix this with more comments or naming tricks, but that just creates another layer of noise. The real fix is to move logic out of the page and lean on JSTL and EL to express the view. When the page only speaks data and presentation, you can reason about it, you can review it quickly, and you stop breaking it with tiny changes.
\n \n\n \nJSTL and EL to the rescue
\n \n\n \nJSP got a lot better once Expression Language became first class and JSTL landed in every container worth using. You can write clean conditions with c:if and loops with c:forEach, format numbers and dates with fmt, and decide fragments with c:choose, all without dropping into Java. Your page turns into a true template that just binds data the controller gives it. For cross cutting display rules, reach for custom tags or tag files. They keep the markup readable and hide the messy details behind a simple tag that designers can live with. This keeps business rules out of the view and makes reuse much easier. I still see folks reach for scriptlets to check a null or format a date. That is needless pain today. EL handles nulls kindly and JSTL has you covered for everyday needs. The more you push toward tags and EL, the more your JSP starts to feel like a real view layer rather than a code dump.
\n \n\n \nMove logic to controllers and helpers
\n \n\n \nThe page is not the place to decide prices or choose which query to run. That work belongs in servlets, controllers, and service classes where you can test and wire things with a clear mind. If you are on Struts, keep actions skinny and push rules into services and simple POJOs. If you are on Spring MVC, bind to command objects, apply validators, and hand the JSP a tidy model. Even on a plain servlet with JSP, you can send a small map of view data and keep the heavy lifting out of the page. Put tiny formatting quirks into helpers or tags so the template stays readable. This helps with caching, with i18n, and with team work. Designers can change structure without fear, and developers can refactor logic with tests that do not run a container. With Ajax getting friendlier through jQuery and friends, it is even more important to keep server pages clean. Your JSON action can be a controller method and your JSP can stay a template instead of becoming a script hub.
\n \n\n \nA plan for legacy apps with zero downtime
\n \n\n \nMost of us are not starting fresh. We have a pile of JSPs with scriptlets, some dating back to the early days of our app. The way out is to refactor in small slices. Pick one page, find the top three scriptlets, and move that logic into a controller or a helper. Replace the scriptlets with JSTL and EL, add a tag for any repeated pattern, and commit. Keep a quick checklist: no database calls in JSP, no new objects with business meaning created in the view, no flow control that the controller should own. Turn conditionals into model flags and lists into prepared collections. Each pass makes the next pass easier because the page becomes a simple consumer of data. Run through this while you ship features, not as a big bang rewrite. Put a tiny rule in code review that says a new scriptlet is not allowed. That single rule stops the leak, and your pages slowly get sane without breaking release dates or sleep cycles.
\n \n\n \nSummary
\n \n\n \nScriptlets feel quick, but they cost you time when your app grows. Keep logic out of JSP and use JSTL, EL, custom tags, and helpers so your pages read like templates and not like puzzles. Push decisions into controllers and services, hand views clean data, and test the rules where tests are easy. Tackle legacy pages one small step at a time, ban new scriptlets, and let the code move toward a clean separation while you keep shipping. It pays off in fewer late errors, faster reviews, easier team work, and a user experience that does not throw stack traces when a bean changes name. That is the kind of boring code you want, the kind that lets you spend your late night on a game or a book instead of hunting a bracket in a JSP.
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