<form action="backend" method="get">
            <h1>Bem vindo ao Teacher Points</h1>
            <h3>Sistema web para calcular pontuação de Professores.</h3>
            <table>
            <tr>
                <td>Meses no cargo:</tr>
                <td><input type="text" name="mes_cargo"/></tr>
            </tr>
            <tr>
                <td>Meses na lotação:</tr>
                <td><input type="text" name="mes_lotacao"/></tr>
            </tr>
            <tr>
                <td>Meses na carreira adjunto:</tr>
                <td><input type="text" name="mes_adjunto"/></tr>
            </tr>
            <tr>
                <td>Meses na carreira titular:</tr>
                <td><input type="text" name="mes_titular"/></tr>
            </tr>
            <tr>
                <td>Magisterio: </tr>
                <td><input type="text" name="magisterio"/></tr>
            </tr>
            <td>
                <input type="submit" value="Calcular pontuação"/>
            </td>

            </table>

int mes_cargo = Integer.parseInt(request.getParameter("mes_cargo"));
int mes_lotacao = Integer.parseInt(request.getParameter("mes_lotacao"));
int mes_adjunto = Integer.parseInt(request.getParameter("mes_adjunto"));
int mes_titular = Integer.parseInt(request.getParameter("mes_titular"));
int magisterio = Integer.parseInt(request.getParameter("mes_magisterio"));

HTTP Status 500 - Internal Server Error
type Exception report

messageInternal Server Error

descriptionThe server encountered an internal error that prevented it from fulfilling this request.

exception

java.lang.NumberFormatException: null
note The full stack traces of the exception and its root causes are available in the GlassFish Server Open Source Edition 4.1.1 logs.

GlassFish Server Open Source Edition 4.1.1