erro 500 | Java Servlet: autenticação, autorização e o padrão MVC

jan 13, 2020 1:46:18 PM org.apache.catalina.core.StandardWrapperValve invoke GRAVE: Servlet.service() for servlet [br.com.alura.gerenciador.servlet.UnicaEntradaServlet] in context with path [/gerenciador] threw exception java.lang.NumberFormatException: null at java.lang.Integer.parseInt(Unknown Source) at java.lang.Integer.valueOf(Unknown Source) at br.com.alura.gerenciador.acao.MostraEmpresa.executa(MostraEmpresa.java:18) at br.com.alura.gerenciador.servlet.UnicaEntradaServlet.service(UnicaEntradaServlet.java:42) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) 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:53) 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:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1598) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)

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package br.com.alura.gerenciador.acao;

import java.io.IOException;

import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;

import br.com.alura.gerenciador.modelo.Banco; import br.com.alura.gerenciador.modelo.Empresa;

public class MostraEmpresa {

public void executa(HttpServletRequest request , HttpServletResponse response ) throws ServletException, IOException {

    String paramId = request.getParameter("id");
    Integer id = Integer.valueOf(paramId);

Banco banco= new Banco();
Empresa empresa = banco.buscaEmpresaPelaId(id);

System.out.println(empresa.getNome());

request.setAttribute("empresa", empresa);

RequestDispatcher rd = request.getRequestDispatcher("/formAlteraEmpresa.jsp");
rd.forward(request, response);

} }