Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

Question

Hello everyone ... sorry for my English but I am an Italian boy with a problem that is not answered.
I had to create a web application-service (created in Java with NetBeans 6.7) which is connected to a database postgresql (8.3.5) and for connection to the server using tomcat (3.2.4) through SOAP messages (2_2).
OPERATING SYSTEM: WINXP
I have created classes ... I created the database ... completed the project in NetBeans without any errors ... implemented the necessary libraries in the project (also ).... 8.3.604.jar jdbc tomcat configured and soap ... .. and set the environment variables (soap, mail, send in xerces )...... run the application on the NetBeans appears the login screen of my web service .....
enter username and password (exactly!) and the NetBeans gives me an Exception:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at Intro.loginActionPerformed(Intro.java:522)
        at Intro.access$100(Intro.java:21)
        at Intro$2.actionPerformed(Intro.java:111)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
        at java.awt.Component.processMouseEvent(Component.java:6263)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
        at java.awt.Component.processEvent(Component.java:6028)
        at java.awt.Container.processEvent(Container.java:2041)
        at java.awt.Component.dispatchEventImpl(Component.java:4630)
        at java.awt.Container.dispatchEventImpl(Container.java:2099)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
        at java.awt.Container.dispatchEventImpl(Container.java:2085)
        at java.awt.Window.dispatchEventImpl(Window.java:2475)
        at java.awt.Component.dispatchEvent(Component.java:4460)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Java Result: 1
BUILD SUCCESSFUL (total time: 31 seconds)  The line 522 Intro class is as follows:
private void loginActionPerformed(java.awt.event.ActionEvent evt) {                                     
        try {
            URL address= new URL("http://"+ip+":8080/soap/servlet/rpcrouter");
            //Costruzione della chiamata
            Call chiamata = new Call();
            chiamata.setTargetObjectURI("urn:server");
            chiamata.setMethodName("controllaAgenzia");
            chiamata.setEncodingStyleURI(Constants.NS_URI_SOAP_ENC);
            //creazione parametri che dovro' passare al soap
            Vector<Parameter> params = new Vector<Parameter>();
            String u = user.getText();
            String p = String.valueOf(password.getPassword());
            params.addElement(new Parameter("user", String.class, u, null));
            params.addElement(new Parameter("password", String.class, p, null));
            chiamata.setParams(params);//parametri passati al soap
            try {
                //Invocazione RPC
                Response respons = chiamata.invoke(address, "");
                //qui ho la risposta inviata dal server
                *Parameter par = respons.getReturnValue();*
                Object value = par.getValue();
                String REP = String.valueOf(value);
                System.out.println(REP);
                if (REP.equals("ACK_agenzia")) {
                    new MainAgenzia(ip);
                    this.dispose();
                } else if (REP.equals("NACK_agenzia")) {
                    JOptionPane.showMessageDialog(null, "I dati inseriti non sono corretti", "Errore", JOptionPane.ERROR_MESSAGE);
                    password.setText("");
                    user.setText("");
                } The strange thing is that this web service was running just finished the project.
After 4-5 days of its operation has stopped, creandomi this problem.
I think the answer is, the server that is not the case.
I thought all I thought was jdbc, but I can connect to the database, so I do not know what to do and how to proceed.
thanks to all, and thanks to my translator. :P

Answer 1

Parameter par = respons.getReturnValue();There is only one possible reason, "respons" is null.