Info 408 Distributed Applications programming 2 nd semester of Credits: 5 Lecturer: Antoun Yaacoub Ph.D.

Transcription

1 Lebanese University Faculty of Sciences I Master 1 degree Computer Sciences Info 408 Distributed Applications programming 2 nd semester of Credits: 5 Lecturer: Antoun Yaacoub Ph.D.

2 Info 408 Distributed Applications programming /2019 RMI & Serialization Warming Up Chapter VIII 2

3 Learning Objectives Today, you will learn how to implement an RMI client/server application involving.class files that are available locally; learn how to compile and execute such servers. Today, you will NOT understand the fundamental purpose of RMI; understand how RMI works; be able to appreciate the potential danger presented by.class files downloaded from remote locations; know how security managers may be used to overcome the above danger. 3

4 Example 0 Write a Java program that calculates the sum of two integers. 4

5 Example 1 ObjectAddImpl.java ObjectAddInterface.java 5

6 Example 1 Server.java 6

7 Example 1 Client.java 7

8 Compilation and Execution There are several steps that need to be carried out: 1. Compile all files with javac. 2. Compile the implementation class with the rmic compiler: This compiler is one of the utilities supplied with the J2SE. Though it might seem strange to have a compiler operate on anything other than source code, this compiler operates on the.class file generated by the above compilation of the implementation file. Used without any command line option, it will generate both a stub file and a skeleton file.however, Java 2 does not require the skeleton file. If Java 2 is being used, then command line option -v1.2 should be employed, so that only the stub file is generated. This will cause a file with the name ObjectAddImpl_Stub.class to be created. 8

9 Compilation and Execution 3. Start the RMI registry: file.policy 4. Run the server: 9

10 Compilation and Execution 5. Run the client: 10

11 Example 1 Step 1 javac *.java Step 2 rmic v1.2 ObjectAddImpl Client Server 11

12 Example 2 Write an RMI method that calculates the number of occurrences of some character in a word. Use both ObjectStringInterface and ObjectAddInterface to write a program that calculates the number of occurrences of some character in a string of texts: 12

13 Example 2 ObjectStringImpl.java 13

14 Example 2 ObjectStringInterface.java 14

15 Example 2 Server.java 15

16 Example 2 Client.java 16

17 Example 2 Client.java 17

18 Example 2 Compilation and Execution 18

19 Example 3 Develop a simple, RMI-based server (CatServer), which will allow a client to read a text-file line by line. The server provides the following methods: o public boolean openfile(string filename) Opens a file, returns true if file is successfully opened, false otherwise. o public String nextline() Reads and returns the next line from the file. Returns null if end-of-file is reached or if no file has been opened. o public boolean closefile() Close the file which is currently open. Returns true if the file is successfully closed, false otherwise. Develop a client (CatClient), which can connect to the server. The client works like a "remote cat", i.e. it requests a file to be opened by the server and reads the file line-by-line (through nextline()). The client sends the lines one-by-one to std. out while reading from the server. 19

20 Example 3 ObjectCatInterface.java 20

21 Example 3 ObjectCatImpl.java 21

22 Example 3 ObjectCatImpl.java 22

23 Example 3 ObjectCatImpl.java 23

24 Example 3 CatServer.java 24

25 Example 3 CatServer.java 25

26 Example 3 Compilation and Execution 26

27 Example 4 ObjectQuoteImpl.java 27

28 Example 4 ObjectQuoteInterface.java 28

29 Example 4 Quote.java 29

30 Example 4 Server.java 30

31 Example 4 Client.java 31

32 Example 4 Compilation and Execution 32

33 Example 5 For illustration only 33

34 Example 5 ObjectMediaImpl.java 34

35 Example 5 ObjectMediaImpl.java 35

36 Example 5 RMIImage.java 36

37 Example 5 Server.java 37

38 Example 5 Client.java 38

39 Example 5 Compilation and Execution 39

40 Example 5 revisited RMIImage.java NOT SERIALIZABLE 40

41 Example 5 revisited RMIImage.java 41

42 Example 5 revisited Compilation and Execution 42

43 Example 6 Passing objects using TCP PrintWriter out = new PrintWriter(link.getOutputStream(),true); ObjectOutputStream out = new ObjectOutputStream(link.getOutputStream()); out.writeobject(o); Scanner in = new Scanner(link.getInputStream()); ObjectInputStream in = new ObjectInputStream(link.getInputStream()); Object o = (Object)in.readObject(); 43

44 Example 6 Color.java 44

45 Example 6 Server.java 45

46 Example 6 Server.java 46

47 Example 6 Client.java 47

48 Example 6 Client.java 48

49 Example 6 Compilation and Execution 49

50 Example 7 Message Server Implement a server and two clients exchanging messages through a server using a FIFO queue. 50

51 Example 7 Message Server The server MessagePoolImpl implements two remote methods defined in the interface MessagePoolInterface: The method put()accepts a String message as an input from the client, and stores it into the FIFO queue. In the case where the queue is full, the put() operation will fail, and an exception will be thrown. The method get()retrieves the message out of the queue to the client which invokes it. The retrieved message is thus deleted from the queue. In the case where the queue is empty, get() will fail and an exception will be thrown. 51

52 Example 7 Message Server The FIFO queue should have a size of 10 messages. Messages are strings. Implement two clients: 1. MessagePutClient generates messages periodically (1 message per 1 second), 2. MessageGetClient retrieves messages periodically (1 message per 2 second). The message could be the timestamp of the client or any randomly generated string. Make sure that all cases are handled: Retrieving from an empty queue Adding message to a full queue 52

53 Example 7 Message Server 53

54 Example 7 MessagePutClient.java 54

55 Example 7 MessageGetClient.java 55

56 Example 7 MessagePoolImpl.java 56

57 Example 8 Hotel Room Reservation System In this exercise you are asked to program a minimal RMI client/server program. This program will be a room reservation system using RMI. For this exercise you can assume that everybody is reserving the room for a specific period of time. In other words, our system does not give the guests the liberty to choose the dates for the reservation. In addition to this, there are 5 room types with different prices. We have 10 rooms of type 0 which are single rooms that costs 55 Euros a night We have 20 rooms of type 1 which are double rooms that costs 75 Euros a night We have 5 rooms of type 2 which are twin rooms that costs 80 Euros a night We have 3 rooms of type 3 which are triple rooms that costs 150 Euros a night We have 2 rooms of type 4 which are quad rooms that costs 230 Euros a night To implement this system you will have to write a server HotelServer, a client HotelClient, a remote interface RoomManager, and the implementation of the remote interface RoomManagerImpl. 57

58 Example 8 Hotel Room Reservation System The hotel client HotelClient can be run by entering the following commands: java HotelClient: If no options are supplied HotelClient just prints and shows how this command can be used. java HotelClient list <server address>: list the available number of rooms in each price range. The output should look like the following: v rooms of type 0 are available for 55 Euros per night w rooms of type 1 are available for 75 Euros per night x rooms of type 2 are available for 80 Euros per night y rooms of type 3 are available for 150 Euros per night z rooms of type 4 are available for 230 Euros per night The values of v, w, x, y, and z should be the current number of available rooms for each type of room. java HotelClient book <server address> <room type> <guest name>: books a room of the specied type (if available), and registers the name of the guest. java HotelClient guests <server address>: list the names of all the registered guests 58

59 Example 8 Hotel Room Reservation System So, for the list, book, and guests options the HotelClient remotely invokes associated methods in a remote object. The HotelClient gets the results of these remote method invocations back from the HotelServer, and prints them out on its standard output. This exercise is left for you as a simple exercise! 59