Optimize Java Backend: Memory, JSP Caching, and Faster Collections

21. Servlet and Memory Usage: Developers often store large objects in HttpSession, leading to memory spikes when garbage collection doesn't reclaim them. Two solutions: implement HttpSessionBindingListener in session-scoped beans to release resources in valueUnbound(), or invalidate sessions promptly using setMaxInactiveInterval() or server timeout settings.

22. Using Buffer Tags: Some application servers (e.g., WebLogic 6+, OpenSymphony) support JSP buffer tags that cache page fragments or whole pages, reducing execution for repeated requests such as shopping carts, catalogs, and portal homepages.

23. Choosing Include Mechanism: JSP can include external resources via the compile-time <%@ include file="..."%> directive or the runtime action. The directive merges files before compilation, while the action includes the result at request time, useful when the included content changes frequently.

24. Timely Session Cleanup: Default session timeout is usually 30 minutes. When memory is low, servers may swap inactive sessions to disk or serialize them, which is costly. Call HttpSession.invalidate() when a session is no longer needed.

26. HashMap Traversal Efficiency: Iterating over a HashMap using entrySet() is faster than iterating over keySet() and calling get() for each key because the former accesses entries directly without extra hash lookups.

Map<String, String[]> paraMap = new HashMap<String, String[]>();

Set<String> appFieldDefIds = paraMap.keySet();

for (String appFieldDefId : appFieldDefIds) {

String[] values = paraMap.get(appFieldDefId);

}

for (Entry<String, String[]> entry : paraMap.entrySet()) {

String appFieldDefId = entry.getKey();

String[] values = entry.getValue();

}

27. Array vs. ArrayList: Arrays are most efficient but have fixed size; ArrayList offers dynamic growth at the cost of performance. Use arrays when size is known; otherwise, use ArrayList.

28. Prefer HashMap and ArrayList over Hashtable and Vector unless synchronization is required, as the latter incur performance overhead.

29. StringBuffer vs. StringBuilder: StringBuilder is faster because it is not synchronized; use StringBuilder when thread safety is not needed, otherwise use StringBuffer.

30. Avoid using split() frequently because it relies on regular expressions; consider Apache StringUtils.split() or cache results.

Additional optimization tips: set unused objects to null, use final/static where possible, employ buffered streams, enable javac -O, extract common code, avoid large array initializations, store dates as long, shorten identifiers, place static final constants in interfaces, replace multiplication/division with bit shifts, consolidate try‑catch blocks, and move invariant code out of loops.