Department of Computer Science COMP212 – 2020 – CA Assignment 2 Distributed Communications Java RMI Assessment Information Assignment Number 2 (of 2) Weighting 10% Assignment Circulated 4th March 2020 Deadline 26th March 2020, 17:00 UK Time (UTC) Submission Mode Electronic via VITAL Learning outcome assessed (1) An appreciation of the main principles underlying distributed systems: processes, communication, nam- ing, synchronisation, consistency, fault tolerance, and security. Purpose of assessment This assignment assesses the understanding of Java RMI. Marking criteria Marks for each question are indicated under the corre- sponding question. Submission necessary in order No to satisfy Module requirements? Late Submission Penalty Standard UoL Policy. 1 Overall marking scheme The coursework for COMP212 consists of two assignments contributing altogether 20% of the final mark. The contribution of the single assignments is as follows: Assignment 1 10% Assignment 2 10% TOTAL 20% 1 2 Objectives This assignment requires you to write a Java program implementing client-server communi- cation using Remote Method Invocation (RMI). Note that no credit will be given for implementing any other form of client-server communication! 3 Explanation of coursework Imagine you are designing a distributed voting application: While the server is running, a client can connect to the server and vote for 1 out of 3 choices (by means of the method vote, see below). After voting, the client can request the voting results so far. 3.1 Basic Java RMI communication—50% of the assignment mark As a first step, you are required to implement client-server communication only. At this stage you can ignore the program logic, but you should show some evidence that your program works and that communication between the client and server actually takes place. For your convenience, we suggest the following remote object interface (however, feel free to modify it to your needs): castVote.java: interface castVote extends java.rmi.Remote { public void vote (int choice) throws java.rmi.RemoteException; public String getVotingResults() throws java.rmi.RemoteException; } You must implement the following classes. 3.1.1 Class castVoteImp.java This class should implement the castVote interface. 3.1.2 Server side The server should initiate and register the remote object. 2 3.1.3 Client side The client should submit the user choice to the remote server and then print the current vote and voting results on screen. Hint. Start with downloading the RMI example from VITAL under the “Assessment Sub- mission” tab. Following the instructions, make sure it works on your computer. Then use that code as a basis for your implementation. 3.2 Program logic—50% of the assignment mark To get further 30%, you need to implement the remote object, the counting of votes and re- turning voting results, and also implement the client side functionality. To get the remaining 20%, you need to extend the communication model to make sure that the server will only allow a client to see the current voting results after submitting its own vote. Hint. Such a functionality can be achieved, for example, by assigning to every client a ticket (a randomly generated integer number). A client without a ticket will be denied all communication. A client first requests a ticket from the server and then passes this ticket as an extra parameter to all remote methods. When the server issues a ticket, it saves the ticket to a data structure (for example, a hash table) so that all remote methods (vote, getVotingResults, etc) will be able to check that the ticket is valid. You are more than welcome to suggest your own method to control the right order of calls. 4 Deadline and Submission Instructions • The deadline for submitting this assignment is Thursday, 26th March 2020, 17:00 UK time (UTC). • Submit (a) The Java source code for all your programs and (b) A README file (plain text) describing how to compile/run your code to produce the various results required by the assignment. Compress all of the above files into a single ZIP file (the electronic submission system won’t accept any other file formats) and specify the filename as Surname-Name- ID.zip. The zip should contain all the appropriate .java and .class files of the client side and server side in two separate directories, one for the client code and the other for the server code. Each directory should contain all the necessary files to run the client/server program including the interface file. Please write a client and a server that run on the same host (localhost) in order to facilitate the execution of the code 3 on our computers. It is extremely important that you adhere to the required format of submission, otherwise we may encounter difficulties in executing and assessing your program! • Submission is via the “Assessment Submission” tab of 201920-COMP212- DISTRIBUTED SYSTEMS on VITAL. Good luck to all! 4
