ServletException

ServletException is a checked exception that forms part of the Java Servlet API and Jakarta EE. It signals that an error has occurred within a servlet or its container, during request processing, initialization, or configuration. The exception is used to indicate problems that the servlet cannot recover from on its own and that should be reported to the container for appropriate handling.

ServletException extends java.lang.Exception. It can be thrown by servlet methods such as init, service, and the HTTP method handlers (doGet, doPost, doPut, doDelete, etc.). Because it is a checked exception, methods declaring it must either catch it or declare it in their own throws clause.

The class provides several constructors, including a no-argument form, one that accepts a detail message, one that accepts both a message and a root cause, and one that accepts only a root cause. The underlying cause can be retrieved via getRootCause() or getCause(), enabling exception chaining and root-cause analysis.

Common usage involves wrapping lower-level exceptions in a ServletException to propagate a meaningful error to the container. For example, catching a database error and throwing new ServletException("Database access failed", e). The container typically translates ServletException into an HTTP 500 Internal Server Error response, and developers can configure custom error pages or mappings for specific exceptions.

Notes include that in newer Jakarta EE versions the package name changes from javax.servlet to jakarta.servlet, though the semantics remain the same. Best practices suggest providing user-friendly, non-sensitive messages and letting the container present appropriate error handling while preserving the root cause for diagnostics.