Servlet

A servlet is a Java programming language class that runs on a servlet container or application server and extends the capabilities of servers that host applications accessed via a request-response programming model. Servlets are typically used to create dynamic web content, handle user input, manage sessions, and provide services such as RESTful endpoints.

Servlets follow a defined lifecycle managed by the container. When deployed, a servlet instance is created and initialized with a call to its init method. For each client request, the container calls the service method, which typically dispatches to specific methods like doGet or doPost in HttpServlet, passing in request and response objects. After the servlet is no longer needed, the container calls destroy to release resources. Instances may be reused across multiple requests and threads, so thread safety and stateless design are important considerations.

The core of the Servlet API includes interfaces and classes such as Servlet, GenericServlet, HttpServlet, HttpServletRequest, HttpServletResponse, ServletConfig, and ServletContext. Web components are often declared in web.xml or via annotations such as @WebServlet. A servlet is packaged in a WAR file and deployed to a servlet container such as Tomcat, Jetty, or WildFly. Modern development frequently uses frameworks that embed a servlet container inside an application.

In addition to basic request handling, the API supports features like filters, listeners, and asynchronous processing introduced in newer specifications. Sessions, cookies, and security integration are common concerns in servlet-based applications. Servlets are a cornerstone of Java web development and underpin many RESTful services and dynamic web content.

Historically part of Java EE, the servlet specification is now maintained under Jakarta EE and related projects. It originated to provide a standard, portable method for extending server behavior with Java, and has influenced web technology for decades.