Servlet and servlet life cycle
- 2. ▪ Servlet ▪ Servlet lifecycle diagram ▪ Methods of lifecycle ▪ init() ▪ service() ▪ doGet() ▪ doPost() ▪ destroy() ▪ References
- 3. Servlet ❏ Servlet is java class which extends the functionality of web server by dynamically generating web pages. ❏ Servlet technology is used to create Dynamic web application ❏ Servlet technology is robust and scalable . ❏ Before Servlet, Common Gateway Interface scripting language was popular as a server-side programming language.
- 5. Servlet Life Cycle: init() Servlet class is loaded The class loader is responsible to load the servlet class. The servlet class is loaded when the first request for the servlet is received by the web container. Servlet instance is created The web container creates the instance of a servlet after loading the servlet class. The servlet instance is created only once in the servlet life cycle. init method is invoked The web container calls the init method only once after creating the servlet instance. The init method is used to initialize the servlet.
- 6. Servlet Life Cycle: init() Syntax: public void init(ServletConfig config) throws ServletException { //initialization… }
- 7. Servlet Life Cycle: Service() ▪ The service() method is the main method to perform the actual task. ▪ The servlet container calls the service() method to handle requests coming from the client and to write the response back to the client. ▪ Each time the server receives a request for a servlet, the server spawns a new thread and calls service.
- 8. Servlet Life Cycle: Service() Syntax: public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { … }
- 9. Servlet Life Cycle: Service() ▪ The service() method checks the HTTP request type (GET, POST, PUT, DELETE, etc.) and calls doGet, doPost, doPut, doDelete, etc. methods as appropriate. ▪ The doGet() and doPost() are most frequently used methods with in each service request.
- 10. Service: doGet() ▪ A GET request results from request for a URL or from an HTML form, should be handled by doGet() method. Syntax: public void doGet (HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException { // Servlet code … }
- 11. Service: doPost() ▪ A POST request results from an HTML form that specifically lists POST as the METHOD and it should be handled by doPost() method. Syntax: public void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Servlet code … }
- 13. Application ▪ doGet() shall be used when small amount of data and insensitive data like a query has to be sent as a request. ▪ doPost() shall be used when comparatively large amount of sensitive data has to be sent. E.g. Sending data after filling up a form or sending login & password. doGet() & doPost()
- 14. Servlet Life Cycle: Destroy() ▪ The destroy() method is called only once at the end of the life cycle of a servlet. ▪ This method gives your servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities. ▪ After the destroy() method is called, the servlet object is marked for garbage collection.
- 15. Servlet Life Cycle: Destroy() Syntax : public void destroy() { // Finalization code... }
- 16. References ▪ ▪