In this assignment, you are requested to build a system which allows a school pupil to practise multiple choice tests in math. Design and implement a RMI-based Client / Server communication system in Java, which will do the following: ? Client: c1. Connect to server via client_stub. c2. Read and display the prompt message sent (see step s2 in server) by the server. c3. Receives and displays the first math question plus three possible answers from the server. c4. User then selects and inputs only one answer and the client program sends the answer to the server. This process is repeated three times to complete all 3 questions from the server Questions database c5. After the test is over the client accepts and displays the test results and score from the server. ? Server: . s0. [Initialization] Create a RMI-based server which implements a test interface s1.Wait for a client connection s2.When a client connection is accepted send an acknowledgement (a welcome message) as a sting of text. s3. From Questions database, server sends the first test questions plus three possible answers to the client. s4. Receives the answer from the client. Stores and evaluates the answer. This process is repeated three times. s5. After that the server sends all results and score to the client. s6. Close the connection to the client and then loop back and wait for another connection. Questions database: Q1: (A + B)*(A+B) 1. A*A + B*B 2. A*A +A*B + B*B 3. A*A +2*A*B + B*B (correct) Q2: (A + B)*(A – B) 1. A*A + 2*B*B 2. A*A – B*B (correct) 3. A*A -2*A*B + B*B Q3: sin(x)*sin(x) + cos(x)*cos(x) 1. 1 (correct) 2. 2 3. 3 Note: All the communication between the Client and the Server should be in the form of strings. ! Programming Notes Here are a few tips/thoughts to help you with this assignment: • You must use the three questions from Questions database (see above). • Define the remote methods to allow the client to send the answers to the server. • Implement these methods as a remote object. • Write a client to invoke the remote methods. • Use the rmic program to produce a stub and a skeleton. • Use the rmiregistry tool to register the server. ? Defining the Interface In this coursework, firstly you define the server methods. The server receives and reads the list of answers selected by the client. Then it checks that this answer is valid (distinct numbers in the range 1-3): • If not, return an error message to the client. • If yes, check answers and see if the client has answered correctly, then return the score to the client. The server is comprised of an interface and a class. The interface provides the definition for the methods that can be called from the client. Essentially the interface defines the client’s view of the remote object. The class provides the implementation. Define these methods in a Java TestInfo interface. Derive the interface from the Remote class or from java.io.Serializable interface (The interface must extend from java.rmi.Remote. All the method declarations must include the throws java.rmi.RemoteException clause). ? Implementing the Remote Objects on the Server Write the TestInfoImpl class that implements the TestInfo interface and the TestServer class that creates an object and registers it on the server. 1. Write the TestInfoImpl class that contains the actual methods with questions and to receive the answers. 2. Derive the class from the UnicastRemoteObject class 3. Create a TestServer class with a method that creates an object. Register this object with the RMI remote object registry, name and bind it to a port using the Naming class and the bind() or rebind() method. ? Programming the Client Produce the TestClient class that locates the server and invokes the remote methods. The command to start the client will be $ java TestClient rmi://machine/remote_object Where the URL refers to the registry(usually on the same machine that the server runs on, probably localhost). Retrieve the remote object using the Naming class, by passing the use of the registry to the lookup() method. Then make the remote method call on this object. ? Producing the Distributed Objects Finally, compile and run the distributed objects. 1. Compile all the classes you have written. 2. Your Java RMI programs are only a part of the application. It uses two other pieces of code called the stub and the skeleton. These reformat the method parameters and encapsulate them into a RMI data unit. This process is called marshalling. Run the command rmic TestInfoImpl to generate the stub and the skeleton. 3. Launch the registry rmiregistry. Be sure to run the registry in the RMI server directory that contains the stub and skeleton. 4. Run the server and the client on a same machine and directory. Then try to run the client and the server on two different machines. ! Submission You should submit your code both on paper and on disk (hand in the assignment to the undergraduate office in the normal way with floppy disk containing only the *.java source code). Write a report on the design and implementation of your solution and answers, showing code and results: (i) a class diagram outlining the class structure for your proposed solution. (ii) a set of summary tables describing the fields, constructors and methods for each class. (iii) a print out of the Java source code of your complete program. ! Extensions A small number of marks are reserved for extensions. These could be to have GUI on client and server sides which send the range of possible choices to the client and validate entries, or to be able to specify a security manager which determines its security policy by using the RMISecurityManager.
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