title: server encountered an unexpected condition that prevented it from fulfilling the request
body: <p>Premiss: I'm a java newbie and this is my first question on stack, I looked over the internet but I can't find any answer.</p>
  
  <p>I started working on a dynamic web project on a windows pc, on eclipse, connected to a mysql database and it was working just fine.</p>
  
  <p>I came home and I wanted to work on it on a mac but I have this problem with the server I guess..</p>
  
  <blockquote>
    <p>Description: "The server encountered an unexpected condition that
    prevented it from fulfilling the request."</p>
    
    <p>Exception: java.lang.NullPointerException</p>
  </blockquote>
  
  <p>I already changed the jdbc and everything but I'm having the same error.
  Do you have any idea or suggestion to help me solve this problem?</p>
  
  <p>Thank you</p>
  
  <p><strong>Edit 1</strong></p>
  
  <p>Full Stack</p>
  
  <blockquote>
    <p>mar 30, 2018 2:09:45 AM org.apache.catalina.core.StandardWrapperValve
    invoke GRAVE: Servlet.service() for servlet [webUI.PersonaServlet] in
    context with path [/WebSalari] threw exception
    java.lang.NullPointerException    at
    database.DbAccessore.eseguiSelect(DbAccessore.java:73)    at
    database.FilmDbAccess.caricaTutteLePersone(FilmDbAccess.java:14)  at
    contenitori.ContenitoreFilm.caricaDati(ContenitoreFilm.java:24)   at
    webUI.PersonaServlet.processRequest(PersonaServlet.java:83)   at
    webUI.PersonaServlet.doPost(PersonaServlet.java:49)   at
    javax.servlet.http.HttpServlet.service(HttpServlet.java:661)  at
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)  at
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
      at
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
      at
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at
    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
      at
    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
      at
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
      at
    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
      at
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
      at
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
      at
    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
      at
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
      at
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
      at
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
      at
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
      at
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
      at
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
      at
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:748)</p>
  </blockquote>
  
  <p>I'm also getting this ClassNotFoundException when trying to connect to the database</p>
  
  <p><strong>Edit 2</strong></p>
  
  <p>Here's my DBAccessore.eseguiSelect method</p>
  
  <pre><code>Connection conn;
  
      public ResultSet eseguiSelect(String p_sql) {
          ResultSet rs = null;
  
          try {
              Statement comando = conn.createStatement(); // Line 73
              rs = comando.executeQuery(p_sql);
          } catch (SQLException sqle) {
              LogManager.scriviLog("Errore nella esecuzione della 
              query! Dettagli:");
          LogManager.scriviLog(sqle.getMessage());
          }
  
          return rs;
      } // end method
  </code></pre>