1. import processing.serial.*;
2. import java.text.*;
3. import java.util.*;
4. 
   
5. PrintWriter output;
6. DateFormat fnameFormat= new SimpleDateFormat("yyyyMMdd");
7. String fileName;
8. 
   
9. Serial myPort;       
10. short portIndex = 0;  
11. float floatvalue;
12. String stringvalue;
13. 
    
14. 
    
15. void setup()
16. {
17.   size(200, 200);
18.   // Open whatever serial port is connected to Arduino.
19.   String portName = Serial.list()[portIndex];
20.   println(Serial.list());
21.   println(" Connecting to -> " + Serial.list()[portIndex]);
22.   println(portName);
23.   myPort = new Serial(this, portName, 9600);
24.   Date now = new Date();
25.   fileName = fnameFormat.format(now);
26.   println(fileName);
27.   output = createWriter(fileName+".txt"); // save the file in the sketch folder
28.   
29. }
30. 
    
31. void draw()
32. {
33.   while(myPort.available()>0)
34.   {
35.   
36.      stringvalue=myPort.readString();
37.      floatvalue=float(stringvalue);
38.      if(floatvalue!=Float.NaN)
39.      {
40.        output.println(floatvalue);
41.      }
42.        
43.   }
44.    
45. }
46. 
    
47. void keyPressed() {
48. output.flush(); 
49. output.close(); 
50. exit();
51. }

and the result