The laziest solution is test whether the variable responsible to store an object's instance is null after the attempt!  

I assume that the sketch throws an exception when attempting to access the webserver when it is unavailable.

Java prvides the try-catch construct which will catch an exception and allow the user to decide what to do with it.

Very basic example of using this construct e.g.

1. void setup() {
2.   try {
3.     // code that might throw an exception
4.     int x = 7/0; // division by zero is not permitted
5.   }
6.   catch(Exception e) {
7.     // an exception was thrown so decide what to do with it
8.     String className =  e.getClass().getSimpleName();
9.     println("Name of exception class: " + className);
10.     println("Division by zero is not permitted");
11.   }
12. }

Hello,

I've already written as you suggest, but Client class doesn't throw an exception. Indeed, the application freezes for a few seconds and afterwards I get an answer at the command prompt showing that there is no connection to the webserver.

This is my code (just a modification of the Client class example):

1. /**
    * HTTP Client.
    *
    * Starts a network client that connects to a server on port 80,
    * sends an HTTP 1.0 GET request, and prints the results.
    *
    * Note that this code is not necessary for simple HTTP GET request:
    * Simply calling loadStrings("http://www.processing.org") would do
    * the same thing as (and more efficiently than) this example.
    * This example is for people who might want to do something more
    * complicated later.
    */
   
   
   import processing.net.*;
   // import processing.xml.*;
   
   XML xml;
   Client c;
   String data;
   
   void setup() {
     size(200, 200);
     background(50);
     fill(200);
     try {
       c = new Client(this, "192.168.1.41", 8081); // Connect to server on port 8081
     }
     catch(Exception e) {
       // an exception was thrown so decide what to do with it
       String className =  e.getClass().getSimpleName();
       println("Name of exception class: " + className);
       println("Not available");
     }
   }
   
   void draw() {
     if (c.available() > 0) { // If there's incoming data from the client...
       data = c.readString(); // ...then grab it and print it
       println(data);
     }
   }
   

and I get this at the terminal:

I would like:

1) Avoid that my application freezes while waiting for an answer;
2) Adjust the connection time to any value;
3) Let the application know that there is a connection problem.

Thanks in advance!



SAM

Thanks, quarks, for you post! 

Thanks, quarks, for you post! 

1) You might want to use a thread.
3) As said, if there is a problem, the client is null.

Processing generally doesn't let exceptions to be exposed, so try / catch is useless most of the time (new APIs in the 2.0 can expose them for "advanced usage").
So, for 2) and more, indeed, you might need to use java.net.Socket directly.

Thanks, PhiLho!

This post has some links related to Thread:

Finally it works fine.
Thanks for all your rich and worthy comments!

SAM