Welcome to the Java Programming Forums


The professional, friendly Java community. 21,500 members and growing!


The Java Programming Forums are a community of Java programmers from all around the World. Our members have a wide range of skills and they all have one thing in common: A passion to learn and code Java. We invite beginner Java programmers right through to Java professionals to post here and share your knowledge. Become a part of the community, help others, expand your knowledge of Java and enjoy talking with like minded people. Registration is quick and best of all free. We look forward to meeting you.


>> REGISTER NOW TO START POSTING


Members have full access to the forums. Advertisements are removed for registered users.

Results 1 to 2 of 2

Thread: Basic Operational Question on Tomcat/Servlets

  1. #1
    Junior Member
    Join Date
    Dec 2010
    Posts
    1
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Question Basic Operational Question on Tomcat/Servlets

    OK; so I'm new to the whole servlet/java/webapps thing, but I'm steadily learning. I just have a quick question on the basic operation of how they work. Let me explain my setup.

    I have a Google Chrome extension that takes some input from the user, and then forwards that input (using an xmlhttprequest) on to a tomcat server which has a servlet on it. That servlet processes the request and then sends back a response.

    My question is this: Is a new instantiation of the java servlet created every time I make the request to the server, or is one instance persisting for the life of the server? My servlet will give predictions based on past history, so it's rather important that it can remember things from the past.

    Thanks so much for your help.


  2. #2
    Super Moderator Json's Avatar
    Join Date
    Jul 2009
    Location
    Warrington, United Kingdom
    Posts
    1,274
    My Mood
    Happy
    Thanks
    70
    Thanked 156 Times in 152 Posts

    Default Re: Basic Operational Question on Tomcat/Servlets

    In the lifecycle of a webapp container and according to the servlet spec the container (Tomcat) should only ever create one instance of each servlet class, therefore the class itself is not threadsafe per such as you should not have class member variables that you write to from the doGet/doPost methods.

    You can think of it as two requests can come in to the servlet at the same time, however because of the way Java works even though both requests hit the same servlet instance they will be in two different threads so therefore two different method stacks will be created when the doGet/doPost methods are called. However if you now try to write to a servlet class member from that method both request threads will potentially overwrite each others values as they use the same object.

    To solve your issue with give response based on previous answers etc you can use the session object. See HttpSession (Servlet API Documentation)

    The session is something that tomcat magically takes care of for you so you don't need to worry about that, all you need to do is grab the session off the request object and then you can store values in it such as previous answers etc. and the next time that session makes another request you can grab those values from the session and base your new answers from that.

    Hope this makes some sense.

    // Json

Similar Threads

  1. JAAS implementaion for web application with tomcat
    By singharun in forum Java Servlet
    Replies: 0
    Last Post: August 30th, 2010, 06:56 AM
  2. [SOLVED] Asking what I suspect to be a very basic question
    By Noobert in forum What's Wrong With My Code?
    Replies: 3
    Last Post: May 24th, 2010, 08:42 AM
  3. Tomcat startup message
    By Lotfus in forum Java Servlet
    Replies: 3
    Last Post: May 10th, 2010, 09:47 AM
  4. How to link two classes in java to use it method
    By Sterzerkmode in forum Object Oriented Programming
    Replies: 3
    Last Post: May 13th, 2009, 07:52 AM
  5. Issues with Tomcat 6.0
    By sanyog24681 in forum Java Servlet
    Replies: 0
    Last Post: October 21st, 2008, 08:55 AM