jiachenz/cs5300-project-1a

Spring 2013 Project 1a in CS5300 @ Cornell University by Alan Demers

CS5300 Project 1a - Submitted Feb 28 2013 by Chantelle Farmer (csf25), Ben Perry (bap63) & Matthew Green (mcg67)

Running The Project

You can run our assignment by deploying the compiled WAR file to a tomcat server. Using eclipse, you can run our project by creating a new dynamic webproject called CS5300P1, then merging this entire directory with the blank project or import the .war file. Run using a tomcat 7 webserver.

If you plan to deploy the war file to an Amazon Elastic Beanstalk instance you must have an application and an environment setup. You will then upload the war file to the interface and then finally when you launch the application, you will need to add the path '/Controller' to the root. Example: http://mcg67test.elasticbeanstalk.com/Controller. Please note this instance is not currently active.

Overall Structure

• The session ID is generated from a timestamp appended to the client's IP address, with all special characters removed. This format guarantees that it will be unique even across multiple session stores.
• Cookies contain this session ID so the server can access an existing session.
• Sessions are stored in a ConcurrentHashMap structure, keyed on session ID.
• Sessions are timed out after 10 minutes of inactivity.
• Every 30 minutes, a cleanup daemon removes expired entries from the session table.

Cookie Format

The data stored in our cookie consists of 3 elements, delimited by a "#": sessionID, version, locations sessionID = the unique ID for the session, created as described above version = the session version #, which starts with 1 and is incremented with each request locations = server(s) which store the session data; currently this consists of a single element, the local application server IP address. (This will be expanded in part b to hold multiple server addresses.)

Session Table Design

The session table is stored in a ConcurrentHashMap structure, keyed on session ID. This structure is threadsafe, so does not require us to provide any external locking mechanisms. The format of our session table data is an array of strings: data, version, expires, expiresTimestamp data = the message that is displayed to the user at the top of the page version = the session version ID, consistent with what is stored in the cookie expires = a string representation of the session expiration time expiresTime = a timestamp representation of the expiration

Description Of The Files

We have three files that are used in this Dynamic Web Project. The first is our Controller which is called Controller.java, the second our custom session object class called Session.java and finally, the daemon function which is in a class called Cleanup.java

Controller.java ~~ The controller in this assignment takes on the function of both the View and the Controller (from MVC architecture). This class is what receives GET and POST requests from a client, creates the session object(our storage mechanism), as well as handles the modifications and issue of our custom cookie 'CS5300PROJ1SESSION'. This class is also responsible for the generation of HTML (aka the web form / UI) and for invoking the daemon cleanup process for the hashmap (see Cleanup.java).

Session.java ~~ Session defines our object whereby client sessions are stored. This class creates our session table as well as session objects. When a user issues a GET request to our site, the controller creates a new cookie that is passed back and forth between client and server containing a unique session ID. That session ID is used as a key to store and retrieve the 'message' from the ConcurrentHashMap in this class. The Session class handles all major operations relating to the table except for cleanup, which is defined below.

Cleanup.java ~~ This file essentially extends the timer class in Java and sets up a service which checks our ConcurrentHashMap, reads through it and compares the time NOW to the timestamp in the table.
If the difference is greater than 600 seconds (10 minutes), the entry is removed and space in the table is freed. This process is invoked by the constructor of the Controller.