Erro que nao consigo resolver

Sou iniciante nessa área e estou estudando no Senai…
professor passou um exemplo que na sala de aula funciona perfeito… em minha casa nao consigo…

alguem pode me ajudar?

segue o erro:

org.apache.jasper.JasperException: java.lang.NullPointerException

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:473)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:403)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:347)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)

at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)

at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)

at io.undertow.jsp.JspFileHandler.handleRequest(JspFileHandler.java:32)

at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)

at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)

at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)

at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)

at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)

at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)

at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:53)

at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)

at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)

at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59)

at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)

at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)

at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)

at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)

at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)

at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)

at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)

at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)

at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)

at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)

at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)

at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)

at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)

at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)

at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)

at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)

at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)

at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)

at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)

at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)

at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)

at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)

at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)

at io.undertow.server.Connectors.executeRootHandler(Connectors.java:326)

at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:812)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)

at java.lang.Thread.run(Thread.java:748)

Caused by: java.lang.NullPointerException

at org.apache.jsp.agenda_jsp._jspService(agenda_jsp.java:137)

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)

… 44 more

<%<a class="mention" href="/u/page">@page</a> import=“br.com.aluno.entity.Aluno”%>

<%<a class="mention" href="/u/page">@page</a> import=“java.util.Collection”%>

<%@ page language=“java” contentType="text/html; charset=ISO-8859-1"

pageEncoding=“ISO-8859-1”%>

<%<a class="mention" href="/u/page">@page</a> import=“java.util.Iterator”%>

Insert title here

<form method="POST">
	<label for="nome">Nome: </label>
	<input name="nome" id="nome"/><br/>
	<label for="curso">Curso: </label>
	<input name="curso" id="nome"/><br/>
	<input type="submit" value="Gravar" name="action"/>
</form>
<%
@SuppressWarnings("unchecked")
Collection<Aluno> alunos = (Collection<Aluno>) request.getAttribute("alunos");
	if(!alunos.isEmpty()){
%>
	<table>
		<tr>
			<td>Nome</td>
			<td>Curso</td>
		</tr>
		<%
			Iterator<Aluno>	it = alunos.iterator();
			while(it.hasNext()){
					Aluno aluno = it.next();
		%>
		<tr>
			<td><%=aluno.getNome()%></td>
			<td><%=aluno.getCurso()%></td>
			<td>
				<form method="POST">
					<input type="hidden" name="id" value="<%=aluno.getId()%>" />
					<input type="submit" name="action" value="Excluir" />
				</form>
			</td>	
		</tr>	
		<%
		}
		%>
	</table>
<%
}
%>

3 Respostas

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