Learning Processing: A Beginner's Guide to Programming Images ...

362 Learning Processing
import processing.net.*;
Client client;
Th e client constructor requires three arguments— “ this ” , referring again to this PApplet , the IP address we
want to connect to (as a String), and the port number (as an integer).
client = new Client(this, " 127.0.0.1 " , 5204);
If the server is running on a diff erent computer than the client, you will need to know the IP address of
that server computer. In addition, if there is no server running at the specifi ed IP and port, the Processing
sketch will give the error message: “ java.net.ConnectException: Connection refused ” meaning either the
server rejected the client or that there is no server.
Sending to the server is easy using the write( ) function.
client.write( " Hello! " );
Reading messages from the server is done with the read( ) function. Th e read( ) method, however, reads
from the server one byte at a time. To read the entire message as a String, readString( ) is used.
Before we can even contemplate reading from the server, we must be sure there is something to read. Th is
check happens with available( ). available( ) returns the number of bytes that are waiting to be read. We can
determine if there is anything waiting to be read by asking if the number of bytes is greater than zero.
if (client.available() > 0) {
String message = client.readString();
}
Using the code from Example 18-1 , (keyboard input), we can create a Processing client that connects and
communicates with our server, sending messages entered by the user. See Example 19-2.
Example 19-2: Simple therapy client
// Import the net libraries
import processing.net.*;
// Declare a client
Client client;
// Used to indicate a new message
float newMessageColor = 0;
// A String to hold whatever the server says
String messageFromServer = " " ;
// A String to hold what the user types
String typing = " " ;
PFont f;
void setup() {
size(400,200);
// Create the Client
client = new Client(this, " 127.0.0.1 " , 5204);
f = createFont( " Arial " ,16,true);
}
Type text and hit return to send to server.
fi g. 19.3
How does processing make you feel?
Connect to server at 127.0.0.1
(localhost), port 5204