Unexpected EOFexception

[Pan Niko]

I have a JSP file which taking methods from a Java class, the problem is the first time im running Tomcat, when im trying to submit something i have EOFexception, if i press the F5 then page come back normally. Also the method im calling is just scanning the object file and decrease by 1 all elements from an XML file. However instead of decrease by 1, decrease them by 2. Checked how many times method executed per time and i noticed that every action perform twice. Any idea, why?
thank you