Java Persistence API

[Jose Alvarez de Lara]

Hi,

I am developing a web app against glassfish v2ur2 and MySQL 5.0. I am going to use session and entities EJB3 class. And I am having problems to understand the Java Persistence API. I mean:

#1.- Do I need an Entity for any table in the DB?
#2.- On first time I am going to do only select queries, but exists a
relationship type of many-to-many between tables in the DB I solved
with normalization. How do I indicate this relationship in the code?
#3.- I do not use keyGen to generate the PKs. All of them are type of auto-increment.
Is this problematic?
#4.-Do I need an Entity for everyone relation table?

To have you an idea of what I am going to do, it is something like the Duke’s Bank.

Thanks in advance,
Jose Alvarez de Lara

[Jose Alvarez de Lara]

Hi,

A fellow explin me the questions, so it let me develop a simple example.
It has two entities, a stateless session as facade and the app client.

Every entity map a table.

Here is the code,

package entity;

import java.io.Serializable;
import javax.persistence.*;
import static javax.persistence.CascadeType.*;
import java.util.Collection;
import java.util.ArrayList;

/**
 *
 * @author NetbeansUser
 */
@Entity
public class Customer implements Serializable {
    private int id;
    private String name;
    private Collection<Order> orders = new ArrayList<Order>();

    @Id
    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    @OneToMany(cascade=ALL, mappedBy="customer")
    public Collection<Order> getOrders() {
        return orders;
    }

    public void setOrders(Collection<Order> newValue) {
        this.orders = newValue;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (int) id;
        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 Customer)) {
            return false;
        }
        Customer other = (Customer) object;
        if (this.id != other.id) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "entity.Customer[id=" + id + "]";
    }

}

package entity;

import javax.persistence.*;

/**
 *
 * @author NetbeansUser
 */
@Entity
@Table(name="ORDER_TABLE")
public class Order {

    private int id;
    private String address;
    private Customer customer;

    @Id
    @Column(name="ORDER_ID")
    public int getId() {
        return id;
    }

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

    @Column(name="SHIPPING_ADDRESS")
    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @ManyToOne()
    @JoinColumn(name="CUSTOMER_ID")
    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }
}

package ejb;

import javax.ejb.Remote;
import entity.Customer;

/**
 *
 * @author NetbeansUser
 */
@Remote
public interface Test {
    // Insert Customer and Orders
    public String testInsert();

    // Verify that all are inserted
    public String verifyInsert();

    // Remove Customer and Orders
    public String testDelete(int id);

    // Verify that all are removed
    public String verifyDelete();

    // Get a detached instance of a Customer
    public int findCustomer(String name);

    public Customer findCustomer(int id);
}

package ejb;

import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import java.util.Collection;
import java.util.List;

import entity.*;

/**
 *
 * @author NetbeansUser
 */
@Stateless(name="ejb/Test")
public class TestBean implements Test {
    
    // Add business logic below. (Right-click in editor and choose
    // "Insert Code > Add Business Method" or "Web Service > Add Operation")
    @PersistenceContext(unitName="pu1")
    private EntityManager em;

    public String testInsert() {

        // Create new customer
        Customer customer0 = new Customer();
        customer0.setId(1);
        customer0.setName("Joe Smith");

        // Persist the customer
        em.persist(customer0);

        // Create 2 orders
        Order order1 = new Order();
        order1.setId(100);
        order1.setAddress("123 Main St. Anytown, USA");

        Order order2 = new Order();
        order2.setId(200);
        order2.setAddress("567 1st St. Random City, USA");

        // Associate orders with the customer. The association
        // must be set on both sides of the relationship: on the
        // customer side for the orders to be persisted when
        // transaction commits, and on the order side because it
        // is the owning side.
        customer0.getOrders().add(order1);
        order1.setCustomer(customer0);

        customer0.getOrders().add(order2);
        order2.setCustomer(customer0);

        return "OK";
    }

    public String verifyInsert() {

        int id = findCustomer("Joe Smith");

        Query q = em.createQuery("select c from Customer c where c.id = :id");
        q.setParameter("name", id);
        Customer c = (Customer)q.getSingleResult();

        Collection<Order> orders = c.getOrders();
        if (orders == null || orders.size() != 2) {
            throw new RuntimeException("Unexpected number of orders: "
                    + ((orders == null)? "null" : "" + orders.size()));
        }

        return "OK";
    }

    public String testDelete(int id) {

        Customer c = findCustomer(id);

        // Merge the customer to the new persistence context
        Customer c0 = em.merge(c);

        // Delete all records.
        em.remove(c0);

        return "OK";
    }

    public String verifyDelete() {

        Query q = em.createQuery("select c from Customer c");
        List results = q.getResultList();

        if (results == null || results.size() != 0) {
            throw new RuntimeException("Unexpected number of customers after delete");
        }

        q = em.createQuery("select o from Order o");
        results = q.getResultList();

        if (results == null || results.size() != 0) {
            throw new RuntimeException("Unexpected number of orders after delete");
        }

        return "OK";
    }

    public int findCustomer(String name) {

        Query q = em.createQuery("select c from Customer c where c.name = :name");
        q.setParameter("name", name);
        Customer c = (Customer)q.getSingleResult();
        return c.getId();
    }

    public Customer findCustomer(int id){

        Query q = em.createQuery("select c from Customer c where c.id = :id");
        q.setParameter("id", id);
        return (Customer)q.getSingleResult();
    }
}

package client;

import javax.ejb.*;
import ejb.Test;

/**
 * @author NetbeansUser
 */
public class AppClient {

    @EJB(name="ejb/Test")
    private static Test sb;

    public static void main(String[] args) {
        AppClient test = new AppClient();
        test.runTest();
    }


    public void runTest() {

        // Persist all entities
        System.out.println("Inserting Customer and Orders... " + sb.testInsert());

        // Test query and navigation
        System.out.println("Verifying that all are inserted... " + sb.verifyInsert());

        // Get a detached instance
        int id = sb.findCustomer("Joe Smith");

        // Remove all entities
        System.out.println("Removing all... " + sb.testDelete(id));

        // Query the results
        System.out.println("Verifying that all are removed... " + sb.verifyDelete());
    }
}

And I get a NullPointerException. Here is the stacktrace,

19-feb-2009 11:46:36 com.sun.enterprise.appclient.MainWithModuleSupport <init>
ADVERTENCIA: ACC003: La aplicación desencadenó una excepción.
java.lang.NullPointerException
        at client.AppClient.runTest(AppClient.java:28)
        at client.AppClient.main(AppClient.java:21)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.sun.enterprise.util.Utility.invokeApplicationMain(Utility.java:266)
        at com.sun.enterprise.appclient.MainWithModuleSupport.<init>(MainWithModuleSupport.java:449)
        at com.sun.enterprise.appclient.MainWithModuleSupport.<init>(MainWithModuleSupport.java:259)
        at com.sun.enterprise.appclient.Main.main(Main.java:200)
Exception in thread "main" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at com.sun.enterprise.appclient.MainWithModuleSupport.<init>(MainWithModuleSupport.java:461)
        at com.sun.enterprise.appclient.MainWithModuleSupport.<init>(MainWithModuleSupport.java:259)
        at com.sun.enterprise.appclient.Main.main(Main.java:200)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at com.sun.enterprise.util.Utility.invokeApplicationMain(Utility.java:266)
        at com.sun.enterprise.appclient.MainWithModuleSupport.<init>(MainWithModuleSupport.java:449)
        ... 2 more
Caused by: java.lang.NullPointerException
        at client.AppClient.runTest(AppClient.java:28)
        at client.AppClient.main(AppClient.java:21)
        ... 8 more

Any idea?

Best regards,
Jose Alvarez de Lara

[Joe San]

It seems to me that the DI did not work and the sb reference is null. Could you tell us how you are deploying your application?

[Jose Alvarez de Lara]

Thanks for your interesting.

I solved the issue injecting the EJB in a servlet and it worked fine.
So I wanted to go further and develop a web application with three tiers:

#1.- the entities Customer and Order,

#2.- the stateful session ejb CustomerControllerBean and OrderControllerBean that use two JavaBean named CustomerDetails and OrderDetails that represent a Customer and an Order,

#3.- and finally the web tier with some JSPs , a controller Servlet, and two JavaBeans named CustomerBean and OrderBean where I inject the ejb remote interfaces

The idea is to use use the CustomerBean and OrderBean as façade.
Well, as I told you above the firs web application run ok injecting the ejb remote interfaces in the servlet.
But the second and more complicated web application do not works. The problem is the same that you observed in my initial posted application: the injected ejb fails and throw a NullPointerException.

I use Eclipse Ganymede RS1 To develop and deploy the web app on glassfish v2ur2.

Regards,
Jose Alvarez de Lara