identifier 'livroBean' resolved to null | Java e JSF I: Sua aplicação web com JSF2

Quando clico em gravar , aparece este erro

... identifier 'livroBean' resolved to null

XHTML
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://java.sun.com/jsf/html">

<h:body>
    <h1>Novo Livro</h1>
    <h:form>
        <fieldset>
            <legend>Dados do Livro</legend>

            <h:panelGrid columns="2">

                <h:outputLabel value="Título:" for="titulo" />
                <h:inputText id="titulo"/>

                <h:outputLabel value="ISBN:" for="isbn" />
                <h:inputText id="isbn"/>

                <h:outputLabel value="Preço:" for="preco" />
                <h:inputText id="preco"/>

                <h:outputLabel value="Data de Lançamento:" for="dataLancamento" />
                <h:inputText id="dataLancamento"/>

                <h:commandButton value="Gravar" action="#{livroBean.gravar}" />

            </h:panelGrid>
        </fieldset>
    </h:form>
</h:body>
</html>

package br.com.caelum.bean;

import javax.faces.bean.ManagedBean;

@ManagedBean
public class LivroBean {

    public void gravar(){
        System.out.println("Gravando Livro");
    }


}

console:

ADVERTÊNCIA: #{livroBean.gravar}: javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null
javax.faces.FacesException: #{livroBean.gravar}: javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:117)
    at javax.faces.component.UICommand.broadcast(UICommand.java:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:791)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1256)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:958)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    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:745)
Caused by: javax.faces.el.EvaluationException: javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:94)
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:101)
    ... 27 more
Caused by: javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:107)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
    ... 28 more

nov 29, 2016 10:10:37 AM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet [Faces Servlet] in context with path [/jsf-livraria] threw exception [javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null] with root cause
javax.el.PropertyNotFoundException: /livro.xhtml @26,68 action="#{livroBean.gravar}": Target Unreachable, identifier 'livroBean' resolved to null
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:107)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:101)
    at javax.faces.component.UICommand.broadcast(UICommand.java:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:791)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1256)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:958)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
    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:745)

Oi Renato,

Por algum motivo o JSF não está conseguindo encontrar o seu Managed Bean. Pode ser por conflito de versões de JAR na sua aplicação ou por algum problema na configuração.

Qual versão do JSF você está utilizando? Tem o arquivo faces-config.xml presente?

Este arquivo tem um conteúdo assim (para a versão 2.2):

<faces-config
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-facesconfig_2_2.xsd"
    version="2.2">

Dá uma olhada nas bibliotecas do seu classpath e veja se tem mais do que uma versão do JSF por exemplo.

Acontece algum erro na hora de subir a aplicação?

Abraço!