Basically, how long is an instance of a servlet around for? I am kind of guessing it is session scope. However, I suppose it could have some sort of timeout or garbage collection to remove old instances.
11 Answers
The servlet's container is attached to a web server that listens for HTTP or HTTPS requests on a certain port number (port 8080 is usually used during development and port 80 in production). When a client (user with a web browser) sends an HTTP request, the servlet container creates new HttpServletRequest and HttpServletResponse objects (for every new request) and passes them through any defined Filter chain and, eventually, the Servlet instance.
In the case of filters, the doFilter() method is invoked. When its code calls chain.doFilter(request, response), the request and response continue on to the next filter, or hit the servlet if there are no remaining filters.
In the case of servlets, the service() method is invoked(by multiple threads for different request). By default, this method determines which one of the doXxx() methods to invoke based off of request.getMethod(). If the determined method is absent from the servlet, then an HTTP 405 error is returned in the response.
The request object provides access to all of the information about the HTTP request, such as its headers and body. The response object provides the ability to control and send the HTTP response the way you want by, for instance, allowing you to set the headers and the body (usually with generated HTML content from a JSP file). When the HTTP response is committed and finished, both the request and response objects are recycled and made for reuse.
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