MRECW Students E- Learning Point Computer Security Student (CSS)

Working of Java Servlet


A Java servlet is a Java programming language program that extends the capabilities of a server. Although servlets can respond to any types of requests, they most commonly implement applications hosted on Web servers.^[1] Such Web servlets are the Java counterpart to other dynamic Web content technologies such as PHP and ASP.NET.

The following is a typical user scenario of these methods.

1. Assume that a user requests to visit a URL.
   • The browser then generates an HTTP request for this URL.
   • This request is then sent to the appropriate server.
2. The HTTP request is received by the web server and forwarded to the servlet container.
   • The container maps this request to a particular servlet.
   • The servlet is dynamically retrieved and loaded into the address space of the container.
3. The container invokes the init() method of the servlet.
   • This method is invoked only when the servlet is first loaded into memory.
   • It is possible to pass initialization parameters to the servlet so that it may configure itself.
4. The container invokes the service() method of the servlet.
   • This method is called to process the HTTP request.
   • The servlet may read data that has been provided in the HTTP request.
   • The servlet may also formulate an HTTP response for the client.
5. The servlet remains in the container's address space and is available to process any other HTTP requests received from clients.
   • The service() method is called for each HTTP request.
6. The container may, at some point, decide to unload the servlet from its memory.
   • The algorithms by which this decision is made are specific to each container.
7. The container calls the servlet's destroy() method to relinquish any resources such as file handles that are allocated for the servlet; important data may be saved to a persistent store.
8. The memory allocated for the servlet and its objects can then be garbage collected.