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java Servlet technology
 

java Servlet technology

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A good overview of Java Servlet technology is discussed through out.

A good overview of Java Servlet technology is discussed through out.

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    java Servlet technology java Servlet technology Presentation Transcript

    • UNDERSTANDING JAVA SERVLET by Tanmoy Barman
    • Discussions  Client-Server Architecture.  HTTP protocol.  Introduction to Servlet.  J2ee container and architecture.  Servlet Life Cycle.  Functions of servlet container.  Servlet API.  Example of servlet.  Session Management Techniques.  Servlet Collaboration.  Comparing Servlet with CGI.
    • Client server architecture
    • Client server architecture  Server: typically a application for large computers which can handle multiple request simultaneously, can process much faster. The application of server is written in such a way that it cannot be access by the user directly but it waits for another program to connect and then it process the request as need by the user.
    • Client server architecture  Client: an application that runs on simple desktop computers. It has an attractive user interface but itself does not have the data to manipulate instead it takes input from the user, connects the server and the server responds to the request as need by the client using this application.
    • HTTP protocol  HTTP(Hyper Text Transfer Protocol ) is a communication protocol for displaying HTML pages inside web browser.  HTTP are stateless protocol because it treats each request independently and have no knowledge of where the request have came from.  A stateless protocol treats each request and response pair as an independent transaction.  Default port no of HTTP is 80.
    • HTTP protocol  The communication between the web browser and the server are usually done using two methods:- 1. GET. 2. POST.  GET method is used to request data from a specified resource.  POST method is used to submit data from a specified resource.
    • HTTP protocol  GET methods are cached but POST method cannot be cached.  GET methods can be bookmarked but POST methods cannot be bookmarked.  GET methods have length restrictions where as POST methods have no length restrictions.  GET methods remains in history of the web browser whereas the POST methods are not present in the history of the web browser.  GET methods are idempotent but POST methods are non-idempotent.
    • HTTP protocol  The other HTTP methods are:- 1. Trace 2. Put 3. Options 4. Head 5. Delete
    • Introduction to Servlet  Servlet are Java class files which resides on the web server which produces dynamic output web pages when a client request for the particular Servlet.  So to execute a Servlet we need a compiler and a JVM machine inside a web server same as when we need to compile and run a simple java program inside our desktop.
    • Introduction to Servlet  To deploy our servlet inside the web server we need a servlet container.  Servlet container is a java virtual machine inside web server which provides compilation and run time execution of servlet.  “Apache tomcat” is an example of popular servlet container.
    • J2ee container and architecture
    • J2ee container and architecture  Containers are used for deploying and execution service provided by the component.  The various types of container in J2EE:- A. Applet container B. Application client container C. EJB container D. Servlet container
    • Servlet Life Cycle  When the client request for the servlet through the web browser the Servlet container loads the servlet for the first time, it calls the init() method. Before the servlet can respond to any request the init() method need to be finished or the servlet need to be initialize. After the init() method the servlet container marked the servlet as available.
    • Servlet Life Cycle  For each request form the client the servlet container calls the service method on the servlet which is going to process the request. The service method can use all the resources which are marked as available in the init() method.  The destroy() method is called to clean up the resources when the server shuts down or there is a lack of resources. It also calls the save the current state information of the servlet which will be used when the servlet again called for the next time.
    • Functions of servlet container  Manage servlet life cycles.  Register a servlet for one or more URLS.  Encode MIME base response.  Decode MIME base request.  Handles HTTP protocols along with other protocols(ftp,pop,smtp,telnet,etc).  Provide network services with request and responses cycles.
    • Servlet API  The java servlet API consist of two Packages which helps in implementation of the servlet:- 1. javax.servlet 2. javax.servlet.http
    • Servlet API  javax.servlet:- It provides the core functionality of the servlet, this API consist of classes and interfaces which is generic and protocol independent.  javax.servlet.http:- This API consist of classes and interfaces which are HTTP protocol specific.
    • SERVLET API
    • SERVLET API  There are two types of servlet available by default which has been defined in servlet API 1. GenericServlet 2. HttpServlet  GenericServlet : it defines the classes and interfaces which are protocol independent and generic which is define on the javax.servlet package. It defines simple life cycle methods such as init, service, destroy. To write generic servlet we simply have to override the abstract service() method.
    • SERVLET API  Signature of GenericServlet:-  public abstract class GenericServlet extends java.io.lang implements Servlet, ServletConfig, java.io.seriliziable
    • SERVLET API  HttpServlet :- it defines classes and interfaces which are http protocol specific. It extends the GenericServlet class therfore it inherits the GenericServlet methods.  Signature of HttpServlet:-  Public abstract class HttpServlet extends GenericServlet implements java.io.sereliziable
    • Example of servlet  To write our own servlet we have to extend the HttpServlet class.  Public class our_servlet extends HttpServlet { Public void doGet(HttpServletRequest req,HttpServletResponse resp)throws IOException,ServletException{ //code for servlet //the logic of the application } }
    • Example of servlet  teddy_test.java Public void display extends HttpServlet{ Public void doGet(HttpServlet response, HttpSrvlet request)throws IOException,ServletException{ out.println(“<HTML>”); out.println(“< BODY>”); response.setContentType(“text/html”); PrintWriter out=resp.getWriter(); out.println(“<p>Hello World</p>”); out.println(“</ BODY>”); out.println(“< /HTML>”); } }
    • Example of servlet  Reading Form Data using Servlet:-  Servlets handles form data parsing automatically using the following methods depending on the situation:  getParameter(): -You call request.getParameter() method to get the value of a form parameter.  getParameterValues(): -Call this method if the parameter appears more than once and returns multiple values, for example checkbox.  getParameterNames(): -Call this method if you want a complete list of all parameters in the current request.
    • Example of servlet  To get information from an html page  Let assume there are two text box present in html page name “teddy_test.html” <form ACTION=“teddy_servlet.java”> Name:<input type=“text” name=“nme”> Age:<input type=“text” name=“age”> <input type=“submit”>
    • Example of servlet  teddy_servlet.java Public void display extends HttpServlet{ Public void doGet(HttpServlet response, HttpSrvlet request)throws IOException,ServletException{ out.println(“<HTML>”); out.println(“< BODY>”); response.setContentType(“text/html”); Printwriter out=resp.getWriter(); String name=req.getParameter(“name”); String age=req.getParameter(“age”); out.println(“<p>name:-”+name+”age:-”+age+”</p>”); out.println(“</ BODY>”); out.println(“< /HTML>”); } }
    • Session Management Techniques  As HTTP is a stateless protocol it cannot remember the same user over multiple page request and treats the same user as different user.  So, if a user request for a page the server responds when the same user request for the another page the server thinks as another user.  The value or the state of the page need to be retained when we purchasing goods from merchant sites or keep us out of daily login to a particular sites.
    • Session Management Techniques  The are methods to retain this value over many pages:- 1. Cookies. 2. Hidden from fields 3. Url rewriting 4. Http Session
    • Session Management Techniques  Cookies are textual information which are stored on the client file system.  Cookies are send by the web server to the web browser.  Cookies contain cookie name and cookie value.  Advantages:- 1. They are simple to maintain 2. They are maintained by the client no over head of the server.
    • Session Management Techniques  Disadvantage:- 1. It will not work if it is disabled by the web browser. 2. Easy to tamper and one person can impersonate as another user.  Syntax:- Cookie ck_object=new Cookie(“cookie_name”,cookie_value);
    • Session Management Techniques  Hidden from fields, in HTML we have to type an extra field called “hidden” which will not be shown to the user by the web browser but it will pass information to the web server. It contains value from the previous request which will going to process the future request.
    • Session Management Techniques  Advantage:- 1. To process it we do not require any special type of server. 2. It will work where cookies will be disable by the web browser.  Disadvantage:- 1. If an error occurred before the values are saved then the values are lost.
    • Session Management Techniques  Syntax:- <input type=“hidden” name=“” values=“”> This field will not be shown to the user but it will pass information to the app server.
    • Session Management Techniques  Url rewriting, it a technique of appending values to the end of the url, so that when the user clicks on the link the values of the current page will be passed through the url.  Advantage:- 1. No extra form submission is required as in hidden from fields.
    • Session Management Techniques  Disadvantage:- 1. It can only pass textual information. 2. Work with link only.  Syntax:- http://url? name1=value1&name2=value2  Appends value on the end of the url where parameters are separated by „&‟ and name, value pairs are separated by „=„.
    • Session Management Techniques  HttpSession object is completely maintained and created by the Web server. To achieve this there is HttpRequest.getSession() method. This method returns true if there the session is created or creates a session before returning. It is used to identify the user across multiple pages and they can live up to specific time bound by the server.
    • Session Management Techniques  Syntax:- HttpSession ses_object=request.getSession(); ses_object.setAttribute(“ses_name”,ses_value); //to set the session on the web server. ses_object.getAttribute(“ses_name”); // to get the value of the session from the web server.
    • Servlet Collaboration  Servlet collaboration is a technique of sharing information between the servlets.  In servlet collaboration on servlet pass the information directly to the another servlet.  To pass the information directly one servlet need to know about the other.
    • Servlet Collaboration  The servlet collaboration can be achieved by following methods :- 1. forward 2. include 3. sendRedirect
    • Servlet Collaboration  Forward and include is the method of RequestDispatcher interface.  Syntax:- RequestDispatcher rd=response.getRequestDispatcher(“url”); rd.forward(request,reponse);  sendRedirect is the method of HttpServletResponse interface  Syntax:- response.sendRedirect(“url of the redirect servlet”);
    • Servlet Collaboration  Difference between sendRedirect and forward:-  The sendRedirect method is used to send the forwarded address to resources in a new domain or server where as the forward method is used to send the forwarded address to resources inside the server.  In case of forward method the servlet container takes cares of everything, the client and browser is not involved, whereas in case of sendRedirect method the forwarded address is sent to the browser of the client.
    • Servlet Collaboration  In forward, the old request and response is send along with the forwarded address, the old request is going to process the new request. In case of sendRedirect the old request and response is lost and a new response is created by the web server and treated as a new request by the browser.
    • Servlet Collaboration  In forward the forwarded address in not seen by the client; its is transparent whereas in sendRedirect the url is present in the url bar of the web browser.  The forward method is fast than the sendRedirect as it does not require an extra round trip.
    • CGI(Common Gateway Interface) allows the application server to call an external program which is going to process the client http request and respond to it. It creates a new process for each request made by the client. What is CGI?
    • Servlet Vs. CGI  CGI(Common Gateway Interface) scripts creates a separate process for each request made by the client where as servlet is initialize only once and creates threads for each request, so CGI scripts are lead to overhead when there is rise in user.  CGI are more prone to attacks than servlet.  CGI scripts are executed to native to operating system where as servlet are compiled to java byte code which can run anywhere.
    • Servlet Vs. CGI  CGI are platform dependent whereas servlet are platform independent.  Servlet handling of request us much faster than CGI.
    • Thank you