Unit 6 - Netwohhhhhddddrking in Java.pdf

Unit 6 - Netwohhhhhddddrking in Java.pdf

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  Advanced Programming / Java Programming ByMelese E. 1 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Advanced Programming / Java Programming Networkingin Java 2 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Overview • Socket (Berkeley socket) – identifies an endpoint in a network • Sockets are at the foundation of modern networking because a socket allows a single computer to serve many different clients at once, as well as to serve many different types of information • This is accomplished through the use of a port, which is a numbered socket on a particular machine. • A server process is said to "listen" to a port until a client connects to it. • A server is allowed to accept multiple clients connected to the same port number, although each session is unique. • To manage multiple client connections, a server process must be multithreaded or have some other means of multiplexing the simultaneous I/O • Socket communication takes place via a protocol. • Internet Protocol (IP) is a low-level routing protocol that breaks data into small packets and sends them to an address across a network, which does not guarantee to deliver said packets to the destination. • Transmission Control Protocol (TCP) is a higher-level protocol that manages to robustly string together these packets, sorting and retransmitting them as necessary to reliably transmit data. • A third protocol, User Datagram Protocol (UDP), sits next to TCP and can be used directly to support fast, connectionless, unreliable transport of packets • The application layer is identified by the use of ports • TCP/IP reserves the lower 1,024 ports for specific protocols. • A few might be familiar to you. For example, port number 21 is for FTP; 23 is for Telnet; 25 is for e-mail; 43 is for whois; 80 is for HTTP; 119 is for netnews. 3 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Overview • A key component of the Internet (or networking in generals) is the address. • Every computer on the Internet has one. • An Internet address is a number that uniquely identifies each computer on the Net • IPv4 address – 32 bit • IPv6 address – 128 bit • Just as the numbers of an IP address describe a network hierarchy, the name of an Internet address, called its domain name, describes a machine’s location in a name space • For example, www.google.com • Domain names are human readable • But, the computer uses IP addresses to uniquely identify devices • DNS (Domain Name System) – is an application layer protocol which is in charge of converting domain names into IP address and vice versa • In Java, you can develop network applications • Using TCP – connection-oriented reliable transport layer protocol • Using UDP – connectionless unreliable transport layer protocol • Using RMI – the ability to call a method on a remote computer • Java’s networking related classes are defined in the java.net package • Beginning with JDK 11, Java has also provided enhanced networking support for HTTP clients in the java.net.http package 4 By Melese E., Department of Computer Science Wednesday, May 29, 2024 Socket Programming
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  Networking in Java– Socket Programming • Socket – IP address + Port • IP address – identifies the device (computer) • Port – identifies the application on the device • There are two kinds of TCP sockets in Java. • One is for servers, and the other is for clients. • The ServerSocket class is designed to be a "listener," which waits for clients to connect before doing anything. • Thus, ServerSocket is for servers. • The Socket class is for clients. • It is designed to connect to server sockets and initiate protocol exchanges 5 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming • The client – using TCP socket • The creation of a Socket object implicitly establishes a connection between the client and server. • There are no methods or constructors that explicitly expose the details of establishing that connection • The two constructors of the Socket class are • Socket(String hostName, int port) throws UnknownHostException, IOException – Creates a socket connected to the named host and port • Socket(InetAddress ipAddress, int port) throws IOException – Creates a socket using a preexisting InetAddress object and a port • Some of the methods of Socket instance are • InetAddress getInetAddress( ) – Returns the InetAddress associated with the Socket object. It returns null if the socket is not connected • int getPort() – Returns the remote port to which the invoking Socket object is connected. It returns 0 if the socket is not connected • int getLocalPort() – Returns the local port to which the invoking Socket object is bound. It returns –1 if the socket is not bound • InputStream getInputStream( ) throws IOException – Returns s the InputStream associated with the invoking socket • OutputStream getOutputStream( ) throws IOException – Returns the OutputStream associated with the invoking socket • void close() – closes the connection 6 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming import java.net.*; import java.io.*; public class ClientSocket { public static void main(String[] args)throws Exception{ Socket soc = new Socket("localhost", 5000); InputStream in = soc.getInputStream(); //byte oriented OutputStream out = soc.getOutputStream(); //byte oriented //You can attach these io objects to other streams BufferedReader br = new BufferedReader(new InputStreamReader(in)); //character oriented BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(out)); //character oriented bw.write("message for the server"); int c; while((c = br.read()) != -1){ System.out.println((char)c); } soc.close(); } } 7 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming • The Server – using TCP socket • The ServerSocket class is used to create servers that listen for either local or remote client programs to connect to them on published ports. • ServerSockets are quite different from client Sockets. • When you create a ServerSocket, it will register itself with the system as having an interest in client connections. • The constructors for ServerSocket reflect the port number that you want to accept connections on and, optionally, how long you want the queue for said port to be. • The constructors of the ServerSocket class • ServerSocket(int port) throws IOException – Creates server socket on the specified port with a queue length of 50 • ServerSocket(int port, int maxQueue) throws IOException – Creates a server socket on the specified port with a maximum queue length of maxQueue • The methods • Socket accept() - which is a blocking call that will wait for a client to initiate communications and then return with a normal Socket that is then used for communication with the client 8 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming import java.net.*; import java.io.*; public class TheServer { public static void main(String[] args) throws Exception{ ServerSocket ss = new ServerSocket(50001); Socket soc = ss.accept(); BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(soc.getOutputStream())); BufferedReader br = new BufferedReader(new InputStreamReader(soc.getInputStream())); System.out.println(soc.getPort()); bw.write("This is a message from the server"); bw.flush(); int a; while((a=br.read()) != -1){ System.out.print((char)a); } soc.close(); } } 9 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming 10 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Socket Programming • Some important classes of the java.net package • InetAddress class – used to work with IPv4 / IPv6 addresses – uses factory methods to create an object of InetAddress • URL class – used to create Uniform Resource Locator (URL) • DatagramSocket – to work with UDP • DatagramPacket – to work with UDP • URLConnection – to get connected to a specified URL and analyze the connection • UnknownHostException – an exception thrown when trying to connect to an unknown server • MalformedURLException – an exception thrown when the string representing the URL is incorrect 11 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • Remote Method Invocation (RMI) allows a Java object that executes on one machine to invoke a method of a Java object that executes on another machine • This is an important feature, because it allows you to build distributed applications • The java.rmi package contains classes for creating RMI applications – some of the important ones are • Remote interface • Naming class • RemoteException and NotBoundException classes • The java.rmi.server package provides classes for creating an RMI server – the important one is • UnicastRemoteObject class • The MalformedURLException from java.net package is also important 12 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • Steps in creating RMI Server and Client • Step One: Create an interface that extends the Remote interface • This interface specifies the methods that are going to be called by the client • The methods throws RemoteException • Step Two: Create an implementation of the interface created in step one • This implementation class must be a subclass of UnicastRemoteObject and must implement the interface of step one • All the methods specified in the interface must be implemented • Should have at least a default constructor that throws RemoteException • Step Three: Create a class containing the main method • In the main method • Create an object of the implementation of step one • Register this object into the rmi registry of the server • Step Four: Create the client • Copy the interface defined in step one and put it in the folder where the client application is saved • Create a class containing the main method – and in the main method do the following • Declare a reference variable of the interface defined in step one • Search for the registered object • Assign the search result to the reference variable created 13 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • To run and test the application • Compile all the files • Then, being on the server directory, start the rmi registry of the server using the following command • start rmiregistry • Run the server • Then run the client • The interface import java.rmi.*; //Remote and RemoteException classes public interface ServerInterface extends Remote{ public double add(double x, double y) throws RemoteException; } 14 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • The implementation of the interface import java.rmi.*;//RemoteException import java.rmi.server.*;//UnicastRemoteObject public class ServerImplementation extends UnicastRemoteObject implements ServerInterface{ public ServerImplementation() throws RemoteException{ } public double add(double x, double y) throws RemoteException{ return x + y; } } 15 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • The Server Application import java.rmi.*;//Naming and RemoteException import java.net.*; //for MalformedURLException public class ServerMain { public static void main(String[] args) { try{ ServerImplementation si = new ServerImplementation(); Naming.rebind("addition", si); // registering the object in the rmi registry }catch(MalformedURLException e){ }catch(RemoteException e){ } } } 16 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  Networking in Java– Remote Method Invocation • The Client Applciation import java.rmi.*;//Naming, NotBoundException and RemoteException import java.net.*;//MalformedURLException public class RMIClient { public static void main(String[] args){ String serverURL = "rmi://localhost/addition"; try{ ServerInterface si = (ServerInterface)Naming.lookup(serverURL); double x = 55.5, y = 157.2; double sum = si.add(x, y); System.out.println("The sum is " + sum); }catch(MalformedURLException e){ } catch(NotBoundException e){ } catch(RemoteException e){ } } } 17 By Melese E., Department of Computer Science Wednesday, May 29, 2024
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  The End! 18 By MeleseE., Department of Computer Science Wednesday, May 29, 2024