404 NullPointerException with AngularJs Java and Jersey - mysql

Question

I've been asked to make an App with AngularJs, Bootstrap, Java and Tomcat as a server. I'm new with java ee so maybe my error is quite simple, but I can't find a solution.
So when I start the project I see my angular app, but when i press a button and it calls http://localhost:8080/MissingDogPoc/res/dog I get this error:
Http Status 500:
java.lang.NullPointerException
com.gabriel.missingdogpoc.service.AbstractFacade.findAll(AbstractFacade.java:42)
com.gabriel.missingdogpoc.service.DogFacadeREST.findAll(DogFacadeREST.java:69)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:498)
com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185)
com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1511)
com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1442)
com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1391)
com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1381)
com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:538)
com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:716)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
SOLUTION
First if you have a web.xml in your WEB-INF you don't need it as long as you have an "ApplicatiationConfig.java" (This is auto-generated if you follow the netbeans tutorials that are out there)
The code will be like this:
package com.gabriel.missingdogpoc.service;
import java.util.Set;
import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;
#ApplicationPath("api")
public class ApplicationConfig extends Application {
#Override
public Set<Class<?>> getClasses() {
Set<Class<?>> resources = new java.util.HashSet<>();
addRestResourceClasses(resources);
return resources;
}
private void addRestResourceClasses(Set<Class<?>> resources) {
resources.add(com.gabriel.missingdogpoc.service.DogFacadeREST.class);
}
}
Then since Tomcat its a "Web-Server" and not an "Application Server" we need to manage the entities ourselves! So we have to make our Entity manager:
LocalEntityManagerFactory.java
package com.gabriel.missingdogpoc.util;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
#WebListener
public class LocalEntityManagerFactory implements ServletContextListener{
private static EntityManagerFactory emf;
#Override
public void contextInitialized(ServletContextEvent event) {
emf = Persistence.createEntityManagerFactory("com.gabriel_MissingDogPoc_war_1.0-SNAPSHOTPU");
}
#Override
public void contextDestroyed(ServletContextEvent event) {
emf.close();
}
public static EntityManager createEntityManager() {
if (emf == null) {
throw new IllegalStateException("Context is not initialized yet.");
}
return emf.createEntityManager();
}
}
And now since we have our own entity manager we need to use it in our rest service. You will probably have "Abrstract Facade" if you generated it with netbeans, and you will have to replace:
protected abstract EntityManager getEntityManager();
public void create(T entity) {
getEntityManager().getTransaction().begin();
getEntityManager().persist(entity);
getEntityManager().getTransaction().commit();
}
public List<T> findAll() {
getEntityManager().getTransaction().begin();
javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
cq.select(cq.from(entityClass));
List<T> res= getEntityManager().createQuery(cq).getResultList();
getEntityManager().getTransaction().commit();
return res;
}
If you have any problems with the backend you can check my code in github /Gaabooo/MissingDogPoc/

Answer 1

Your problem is that you're using Tomcat, which is an implementation of the Servlet and JSP specifications.
You've tried to turn it into a JavaEE 7 web container by adding Jersey and EclipseLink to it. Unfortunately it will still be missing the integration between the components. In your case, Jersey has no idea that it needs to inject an EntityManager into your DogFacadeREST object, so you get a NullPointerException as soon as you try to call it. Additionally, the #Stateless annotation will be completely ignored because you need to include EJB support as well for this.
It's way easier to use something like WildFly, TomEE or GlassFish and then you can throw away all those dependencies (except for the javaee-web-api).