Transcript 09F-NoteSet15x

CSE 1341 Honors
Professor Mark Fontenot
Southern Methodist University
Note Set 15
Networking
IP: 192.168.0.123
Network
IP: 97.99.88.77
Every computer connected to a network
has a unique ID called an IP Address
IP: 111.222.121.99
Client/Server Model
Data Transfer
Between client and server
ClientActively makes a
Connection to the server
ServerWaits Passively
for a connection from
a client
Each computer has many “ports” that allow it to communicate with
More than one other computer.
On The Server
Pseudocode
Create a server socket on port 8856
while ( no client has connected )
wait for a connection from a client
“handle” the connection from the client
Different Types of Servers:
• E-Mail Server (wait for a mail client like Outlook to connect)
• Web Server (waits for a web client (browser) to
connect and request a webpage)
• FTP Server (waits for a connect and transfer files b/w two
computers
On The Server
• A Server (physical machine) can run many
different services (logical servers) at the same
time.
• Each service is bound to a particular port.
– This means that the service listens or waits for
incoming connections on that port.
– A port is identified by a unique number
• Therefore, to connect to a server running on a
particular port, the client needs to know the
server’s ip address and port number
How to find your computer’s IP
• Mac
– open Terminal app (in utilities)
– type ifconfig
– look for line that says inet
• Windows
– Open command prompt (cmd)
– type ipconfig
– look for line that says IP Address
Note: Every time you connect
to a different network, you could
get a different IP address.
Example Scenario
Network
Client
192.168.0.202
Server
192.168.0.101
Creating a Network Server in Java
Let’s say this server is running on computer w/ IP 192.168.0.101
ServerSocket listener = new ServerSocket(3333);
Socket connection;
//Blocks and waits for some client to attempt to connect
//Will accept the connection only on the port listed above
connection = listener.accept();
//More code to come
So… a client would attempt to connect to IP
192.168.0.101 on port 3333.
Creating a Network Client in Java
Let’s say this client is running on computer w/ IP 192.168.0.202
//attempt to connect to server running at 192.168.0.101
Socket client = new Socket(“192.168.0.101”, 3333);
Communication
• Two computers connected to the same socket can send
and receive information to/from each other
//attempt to connect to server running on
Socket client = new Socket(“192.168.0.101”, 3333);
//Write to socket with a printwriter
PrintWriter output =
new PrintWriter(client.getOutputStream());
//Read from socket with a Scanner – just like from
//the keyboard
Scanner input =
new Scanner (client.getInputStream());
Exception Handling
• Helps recover from runtime errors
– Try to connect to a server but can’t get a connection
• Some methods throw exceptions that must be
caught in the code you write.
try {
//attempt to connect to server running on
Socket client = new Socket(“192.168.0.101”, 3333);
} catch (Exception e) {
System.out.println(“Error”);
System.out.println(e.getMessage());
}
Breakout IN Groups
• Modify Simple Server
– Have server generate a random number between 1
and 10, then wait for a connection
– Upon connection, read a number from the input
stream and check.
– Send back to client a message of correct guess or
incorrect guess
• Modify Simple Client
– Get a number between 1 and 10 from the user
– Connect to server and then send number
– Read back response and display to the user