java.lang.NullPointerException while trying to fetch entity by id

Question

I'am using spring and hibernate.

My entity:

package com.igorgorbunov3333.core.entities.domain;

import com.igorgorbunov3333.core.entities.enums.Proceeding;

import javax.persistence.*;
import java.util.Date;

/**
 * Created by Игорь on 03.04.2016.
 */

@Entity
@Table(name = "cases")
@NamedQueries({
    @NamedQuery(name = "getAllCases", query = "SELECT c FROM Case c JOIN FETCH c.client JOIN FETCH c.firstInstance " +
            "JOIN FETCH c.secondInstance JOIN FETCH c.thirdInstance JOIN FETCH c.category")
})
public class Case {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;

    @Column(name = "case_number")
    private String caseNumber;

    @ManyToOne
    @JoinColumn(name = "client_id")
    private Client client;

    @OneToOne
    @JoinColumn(name = "first_instance_id")
    private FirstInstance firstInstance;

    @OneToOne
    @JoinColumn(name = "second_instance_id")
    private SecondInstance secondInstance;

    @OneToOne
    @JoinColumn(name = "third_instance_id")
    private ThirdInstance thirdInstance;

    @Enumerated(EnumType.ORDINAL)
    private Proceeding proceeding;

    @Temporal(TemporalType.DATE)
    @Column(name = "closing_date")
    private Date closingDate;

    @ManyToOne
    @JoinColumn(name = "category_id")
    private Category category;

    private float price;

    public long getId() {
        return id;
    }

    public String getCaseNumber() {
        return caseNumber;
    }

    public Client getClient() {
        return client;
    }

    public FirstInstance getFirstInstance() {
        return firstInstance;
    }

    public SecondInstance getSecondInstance() {
        return secondInstance;
    }

    public ThirdInstance getThirdInstance() {
        return thirdInstance;
    }

    public Proceeding getProceeding() {
        return proceeding;
    }

    public Date getClosingDate() {
        return closingDate;
    }

    public Category getCategory() {
        return category;
    }

    public float getPrice() {
        return price;
    }

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

    public void setCaseNumber(String caseNumber) {
        this.caseNumber = caseNumber;
    }

    public void setClient(Client client) {
        this.client = client;
    }

    public void setFirstInstance(FirstInstance firstInstance) {
        this.firstInstance = firstInstance;
    }

    public void setSecondInstance(SecondInstance secondInstance) {
        this.secondInstance = secondInstance;
    }

    public void setThirdInstance(ThirdInstance thirdInstance) {
        this.thirdInstance = thirdInstance;
    }

    public void setProceeding(Proceeding proceeding) {
        this.proceeding = proceeding;
    }

    public void setClosingDate(Date closingDate) {
        this.closingDate = closingDate;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    public void setPrice(float price) {
        this.price = price;
    }
}

spring-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd" >

    <!--@Transaction annotation support -->
    <tx:annotation-driven transaction-manager="transactionManager"/>

    <!--Scanning components in base-package (look for annotations) -->
    <context:component-scan base-package="com.igorgorbunov3333"/>

    <!--Activates various annotations to be detected in bean classes: Spring's @Required and @Autowired and so on-->
    <context:annotation-config/>

    <!--Обеспечивает работу с транзакциями в Spring -->
    <bean id="transactionManager"
          class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="emf"/>
    </bean>

    <!-- Datasource. Источник данных - база MySQL -->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/database" />
        <property name="username" value="root" />
        <property name="password" value="root" />
    </bean>

    <!-- EntityManagerFactory -->
    <bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <!--Поставщик данных - hibernate-->
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />
        </property>
        <!--поиск сущностей в этом пакете-->
        <property name="packagesToScan"
                  value="com.igorgorbunov3333"/>
        <!--детали конфигурации поставщика постоянства (hibernate) -->
        <property name="jpaProperties">
            <props>
                <prop key="hibernate.dialect">
                    org.hibernate.dialect.MySQL5Dialect
                </prop>
                <prop key="hibernate.max_fetch_depth">3</prop>
                <prop key="hibernate.jdbc.fetch_size">50</prop>
                <prop key="hibernate.jdbc.batch_size">10</prop>
                <prop key="hibernate.show_sql">true</prop>
            </props>
        </property>
    </bean>


</beans>

Here I'm getting NullPointerException:

public Case findById(long id) {
    return entityManager.find(Case.class, id);
}

I sure to you - id is correct, but entity can't be found. But when I'm getting all entities all fine:

public List<Case> findAll() {
    Query query = entityManager.createNamedQuery("getAllCases");
    return query.getResultList();
}

What is the reason?

Full track of NPE:

09-Oct-2016 12:40:41.650 SEVERE [http-nio-8080-exec-7] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [ShowSingleCase] in context with path [] threw exception
 java.lang.NullPointerException
    at com.igorgorbunov3333.core.entities.service.impl.CaseServiceImpl.findById(CaseServiceImpl.java:32)
    at com.igorgorbunov3333.web.servlet.display.single.ShowSingleCase.doGet(ShowSingleCase.java:29)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:71)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:108)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:522)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:620)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:1096)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:760)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1480)
    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)

My CaseServiceImpl:

package com.igorgorbunov3333.core.entities.service.impl;

import com.igorgorbunov3333.core.entities.domain.Case;
import com.igorgorbunov3333.core.entities.enums.CaseStatus;
import com.igorgorbunov3333.core.entities.service.api.CaseService;
import com.igorgorbunov3333.core.util.DateUtil;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import java.util.*;

/**
 * Created by Игорь on 27.07.2016.
 */

@Repository
@Service("CaseService")
public class CaseServiceImpl implements CaseService {

    @PersistenceContext
    private EntityManager entityManager;

    public Case findById(long id) {
        return entityManager.find(Case.class, id);
    }
}

Servlet:

package com.igorgorbunov3333.web.servlet.display.single;

import com.igorgorbunov3333.core.entities.domain.Case;
import com.igorgorbunov3333.core.entities.service.api.CaseService;
import com.igorgorbunov3333.core.entities.service.impl.CaseServiceImpl;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

import static com.igorgorbunov3333.web.util.Views.SINGLE_CASE_PAGE;

/**
 * Created by Игорь on 09.08.2016.
 */
@WebServlet(name = "ShowSingleCase", urlPatterns = "/showSingleCase")
public class ShowSingleCase extends HttpServlet {
    private CaseService caseService = new CaseServiceImpl();

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        long id = Long.valueOf(request.getParameter("caseID"));
        Case c = caseService.findById(id);

        request.setAttribute("case", c);

        request.getRequestDispatcher(SINGLE_CASE_PAGE).forward(request, response);
    }
}

Answer 1

As you are creating CaseServiceImpl class object by yourself in your servlet class, entityManager object is not autowire automatically by spring and that is the reason you are getting NullPointerException. either you should autowire service class object into servlet class so that spring will resolve entitymanager dependency by itself and provide you fully configured service object or you should set entity manager object into your service class while creating its object in servlet.

Answer 2

Your problem is in this line:

private CaseService caseService = new CaseServiceImpl();

That's not how dependency injection works. You're instantiating your CaseService object manually. In this case framework won't inject any dependencies so your private EntityManager entityManager; field will be null. Instead you have to annotate your caseService field with @Autowired annotation. That will tell Spring to inject the bean from context:

@Autowired
private CaseService caseService;

Answer 3

The only thing that can be null (is not primitive) on the line you stated that would cause a problem is entityManager, so you're looking for the underlying reason for this, which I don't see in the code you posted.