Lecture 3

Question 1

Which ports are reserved for standard protocols?

Answer 1

0-1023

Question 2

What commands are supported by HTTP?

Answer 2

GET, POST, PUT, DELETE, HEAD, OPTIONS, TRACE

Question 3

What is POP? What’s its port? What commands?

Answer 3

Post Office Protocol

Port 110

USER, PASS, STAT, RETR, DELE, QUIT

Question 4

How is input/output done in java with sockets

Answer 4

Input/output streams

Question 5

How is a socket constructed in java?

Answer 5

Socket s = new Socket(hostname, portnumber);

Question 6

What does the accept() methofd do on a ServerSocket?

Answer 6

Block the thread until a client connects, and when it does, return a Socket object representing that client’s socket.

Question 7

How do you get the input and output streams of a socket?

Answer 7

InputStream in = s.getInputStream();

OutputStream out = s.getOutputStream();

Question 8

What ae object streams?

Answer 8

ObjectInputStream/ObjectOutputStream

Automatically serialises serialisable objects and sends them over the stream, before being deserialised on the other end

Question 9

How does RMI work?

Answer 9

Client calls method on client side proxy

Client side proxy packages the info and sends it via network to the serer side proxy

server side proxy depackages it, makes a call to the local (server) method, and packages the return info up -> sends back to client

client side proxy unpackages the result and gives it to the client

Question 10

What does the RMI program deal with locally?

Answer 10

stubs that implement the interface Remote

Question 11

RMI calls are asynchronous

T or F

Answer 11

F - they are synchronous (blocking)

Question 12

What 5 steps are involved in creating a RMI server?

Answer 12

Define remote interface

Write a remote implementation

Start the RMI registry

Create the remote service

Register the service with the registry

Question 13

What does a remote interface contain?

What constraints are on the methods?

Answer 13

Stub methods that can be implemented on the server

Must declare RemoteException, return values must be primitive or serialisable

Question 14

What is the easiest way to create a RMI server

Answer 14

Extend java.rmi.server.UnicastRemoteObject

Add constructor that can throw RemoteException

Register the service (usually in static main() method)

Question 15

what is an RMI registry?

Answer 15

Service that registers/looks up RMI server objects

Question 16

The RMI registry is typically started on each client machine

T or F

Answer 16

F - it’s started on the server machine

Question 17

Each server requires a separate RMI registry

T or F

Answer 17

F - servers may share registries

Question 18

With a reference to a RMI registry, what else must be done to start an RMI server?

Answer 18

Create a service object

Bind the service object to a name in the registry

Question 19

What is an RMI callback?

Answer 19

Client passes remote object to server

Server can then call methods on that remote object (which execute on the client)

Question 20

what does RMI require to download classes?

Answer 20

A securitymanager

Question 21

How can RMI stuff be made robust?

Answer 21

Use socket timeouts to prevent infinite blocking in case of remote errors