NullPointerException in REST service

Question

I am doing a REST service using Hibernate and Struts in NetBeans where I have created the RESTful service using Jersey JAX-RS RI 2.5.1 and JAX RS 2.0 and I am having a error as follows:

type Exception report

message java.lang.NullPointerException

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

exception

javax.servlet.ServletException: java.lang.NullPointerException
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:392)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:382)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:345)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:220)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)

root cause

java.lang.NullPointerException
    com.myapp.struts.service.AbstractFacade.findAll(AbstractFacade.java:41)
    com.myapp.struts.service.UserTblFacadeREST.findAll(UserTblFacadeREST.java:66)
    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)
    org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:151)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:171)
    org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:195)
    org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:104)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:402)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:349)
    org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:106)
    org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:259)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:318)
    org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:236)
    org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1010)
    org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:373)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:382)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:345)
    org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:220)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)

and My Code is:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.myapp.struts.service;

import com.myapp.struts.UserTbl;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.ws.rs.Consumes;
import javax.ws.rs.DELETE;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.PUT;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;

/**
 *
 * @author Vihaan
 */
@javax.ejb.Stateless
@Path("usertbl")
public class UserTblFacadeREST extends AbstractFacade<UserTbl> {
    @PersistenceContext(unitName = "reststrutsPU")
    private EntityManager em;

    public UserTblFacadeREST() {
        super(UserTbl.class);
    }

    @POST
    @Override
    @Consumes({"application/xml", "application/json"})
    public void create(UserTbl entity) {
        super.create(entity);
    }

    @PUT
    @Path("{id}")
    @Consumes({"application/xml", "application/json"})
    public void edit(@PathParam("id") Integer id, UserTbl entity) {
        super.edit(entity);
    }

    @DELETE
    @Path("{id}")
    public void remove(@PathParam("id") Integer id) {
        super.remove(super.find(id));
    }

    @GET
    @Path("{id}")
    @Produces({"application/xml", "application/json"})
    public UserTbl find(@PathParam("id") Integer id) {
        return super.find(id);
    }

    @GET
    @Override
    @Produces({"application/xml", "application/json"})
    public List<UserTbl> findAll() {
        return super.findAll();
    }

    @GET
    @Path("{from}/{to}")
    @Produces({"application/xml", "application/json"})
    public List<UserTbl> findRange(@PathParam("from") Integer from, @PathParam("to") Integer to) {
        return super.findRange(new int[]{from, to});
    }

    @GET
    @Path("count")
    @Produces("text/plain")
    public String countREST() {
        return String.valueOf(super.count());
    }

    @Override
    protected EntityManager getEntityManager() {
        return em;
    }
    
}

UserTbl.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.myapp.struts;

import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;

/**
 *
 * @author Vihaan
 */
@Entity
@Table(name = "user_tbl")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "UserTbl.findAll", query = "SELECT u FROM UserTbl u"),
    @NamedQuery(name = "UserTbl.findById", query = "SELECT u FROM UserTbl u WHERE u.id = :id"),
    @NamedQuery(name = "UserTbl.findByUsername", query = "SELECT u FROM UserTbl u WHERE u.username = :username"),
    @NamedQuery(name = "UserTbl.findByPassword", query = "SELECT u FROM UserTbl u WHERE u.password = :password"),
    @NamedQuery(name = "UserTbl.findByName", query = "SELECT u FROM UserTbl u WHERE u.name = :name")})
public class UserTbl implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "ID")
    private Integer id;
    @Basic(optional = false)
    @Column(name = "username")
    private String username;
    @Basic(optional = false)
    @Column(name = "password")
    private String password;
    @Basic(optional = false)
    @Column(name = "name")
    private String name;

    public UserTbl() {
    }

    public UserTbl(Integer id) {
        this.id = id;
    }

    public UserTbl(Integer id, String username, String password, String name) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof UserTbl)) {
            return false;
        }
        UserTbl other = (UserTbl) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "com.myapp.struts.UserTbl[ id=" + id + " ]";
    }
    
}

this is the AbstractFacade class

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.myapp.struts.service;

import java.util.List;
import javax.persistence.EntityManager;

/**
 *
 * @author Vihaan
 */
public abstract class AbstractFacade<T> {
    private Class<T> entityClass;

    public AbstractFacade(Class<T> entityClass) {
        this.entityClass = entityClass;
    }

    protected abstract EntityManager getEntityManager();

    public void create(T entity) {
        getEntityManager().persist(entity);
    }

    public void edit(T entity) {
        getEntityManager().merge(entity);
    }

    public void remove(T entity) {
        getEntityManager().remove(getEntityManager().merge(entity));
    }

    public T find(Object id) {
        return getEntityManager().find(entityClass, id);
    }

    public List<T> findAll() {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        cq.select(cq.from(entityClass));
        return getEntityManager().createQuery(cq).getResultList();
    }

    public List<T> findRange(int[] range) {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        cq.select(cq.from(entityClass));
        javax.persistence.Query q = getEntityManager().createQuery(cq);
        q.setMaxResults(range[1] - range[0] + 1);
        q.setFirstResult(range[0]);
        return q.getResultList();
    }

    public int count() {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        javax.persistence.criteria.Root<T> rt = cq.from(entityClass);
        cq.select(getEntityManager().getCriteriaBuilder().count(rt));
        javax.persistence.Query q = getEntityManager().createQuery(cq);
        return ((Long) q.getSingleResult()).intValue();
    }
    
}

It seems that NPE is thrown inside AbstractFacade code. It would give us more insight if you add its source code. — Tomasz Bawor, May 11 '17 at 12:19
Like @AlexFerretti mentioned. Entity manager is probably null. You sould read about nature of NPE, and then you will be able to identify root cause of it and ask more detailed questions. — Tomasz Bawor, May 11 '17 at 12:23
This might help http://stackoverflow.com/questions/11173974/different-ways-of-getting-the-entitymanager — Alex Ferretti, May 11 '17 at 12:27

score 0 · Accepted Answer · answered May 11 '17 at 12:54

0

I just initialized the em using

em = Persistence.createEntityManagerFactory("reststrutsPU").createEntityManager();

this solved my problem

answered May 11 '17 at 12:54

Kunal Dudka

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NullPointerException in REST service

1 Answers1