Boa tarde, Leandro! Como vai?

Vc está obtendo um NullPointerException pq não foi possível criar uma EntityManager.

Vc poderia colar aqui o código que está sendo executada quando dá esse erro?

Oi Leandro, tudo bem ?

Cara você tá levando um nullpointer ai..

Consegue confirmar se está executanto todos os passos ?

CONFIGURANDO SPRING

package br.com.casadocodigo.loja.conf;

 import java.util.Properties;

import javax.persistence.EntityManagerFactory;

import org.springframework.context.annotation.Bean;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.JpaVendorAdapter;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.annotation.EnableTransactionManagement; 


@EnableTransactionManagement//ABILITANDO A TRANSAÇÃO PARA O SPRING TOMA CONTA
public class JPAConfiguration {

    @Bean
    public LocalContainerEntityManagerFactoryBean EntityManagerFactory() {
        LocalContainerEntityManagerFactoryBean factoryBean =    
                new LocalContainerEntityManagerFactoryBean();

        JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        factoryBean.setJpaVendorAdapter(vendorAdapter);

        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setUsername("root");
        dataSource.setPassword("");
        dataSource.setUrl("jdbc:mysql://localhost:3306/casadocodigo");
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");

        factoryBean.setJtaDataSource(dataSource);

        // DIALECT QUE IREMOS USAR EM NOSSA APLICAÇÃO
        Properties props = new Properties();
        props.setProperty("hibernate.dialect", "org.hibernate.dialect.MySQL5Dialect");
        props.setProperty("hibernate.show_sql", "true");// VISUALIZANDO NOSSO SQL
        props.setProperty("hibernate.hbm2ddl.auto", "update");// MAPEAMENTO DO A CADA ALTERAÇÃO O HIBERNATE DA UM UPDATE AUTOMÁTICO NO BANCO
        factoryBean.setJpaProperties(props);

        factoryBean.setPackagesToScan("br.com.casadocodigo.loja.models");// ONDE ELE VAI ENCONTRA AS PROPROENDKDAKDKADKDJ

        return factoryBean;// SE RECLAMAR DA UM CTRL + 1 -- SERÁ SUBSTITUIDO O VOID QUE NAO RETORNA NADA


    }

    @Bean
    public JpaTransactionManager TransactionManager(EntityManagerFactory emf){// FAZENDO TRANSAÇÃO 
        return new JpaTransactionManager(emf);

    }


}

fiz a chamada direitinho JPAConfiguration.class no protected Class

package br.com.casadocodigo.loja.conf;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

// CTRL +1 -- PARA FAZER A IMPORT
// CRTL + ESPAÇO -- PARA DA UM  AUTO COMPLITER



public class ServletSpringMVC extends AbstractAnnotationConfigDispatcherServletInitializer{
    // CONFIGURANDO SPRING PELO CODIGO JAVA MELHOR OPÇÃO OU SE DESEJA CONFIGURA PELO XML
    @Override
    protected Class<?>[] getRootConfigClasses() {

        return null;
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[] {AppWebConfiguracao.class, JPAConfiguration.class};// CLASSE DE CONFIGURAÇÃO DE PROJETO WEB QUE IREMOS UTILIZAR 
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] {"/"};// INFORMANDO QUAL URL O SPRING DEVE MAPEAR NO CASO / EM DIANTE O SPRING TOMARÁ CONTA DO MAPEAMENTO

    }


}

esse erro acontece quando configura essas duas classes acima e a public class ProdutoDAO.

import javax.persistence.PersistenceContext;

import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

import br.com.casadocodigo.loja.models.Produto;

// JPAConfiguration


@Repository//FAZENDO COM QUE O SPRING RECONHEÇA O PRODUTO DAO E MAPEA-LO
@Transactional
public class ProdutoDAO {

    @PersistenceContext
    private EntityManager manager;

    public void gravar(Produto produto){
        manager.persist(produto);

    }
}

erro ao executar aplicação

HTTP Status 500 - Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is java.lang.NullPointerException
type Exception report

message Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is java.lang.NullPointerException

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

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is java.lang.NullPointerException
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

org.springframework.transaction.CannotCreateTransactionException: Could not open JPA EntityManager for transaction; nested exception is java.lang.NullPointerException
    org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:430)
    org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373)
    org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:438)
    org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:261)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653)
    br.com.casadocodigo.loja.daos.ProdutoDAO$$EnhancerBySpringCGLIB$$b789cace.gravar(<generated>)
    br.com.casadocodigo.loja.controllers.ProdutosController.gravar(ProdutosController.java:25)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:781)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:721)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:863)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

preciso da ajuda de vocês