How to pass an entity class in remote method invocation from a Enterprise Client application to EJB

[Arno van Haastert]

Hello,

Having passed my Java Programmer II exam last month I am now diving into the world of java EE, meaning I am quite a newbie on both Java and EE.
Currently I am trying to implement an example from the book "Beginning Java EE 6 platform with glassfish"  from scratch with NetBeans.
The goal is to create a stateless enterprise bean BookEJB that implements a remote interface with createBook(book) and deleteBook(book) methods.
CreateBook should persist the book in a mySql database and deleteBook should delete it from the database.
An Enterprise Application client will remotely call createBook and deleteBook.
Book is an entity class.

I am following the process described in https://netbeans.org/kb/docs/javaee/entappclient.html.
However this example does not involve passing an entity class while invoking the remote methods.
This is exactly where I am getting into trouble..

What I have done:

1) Create a new Java  - Java Class Library project "BookRemote" for the remote interface, e.g.

@Remote
public interface BookEJBRemote {
}

2) Create a Java EE - Enterprise Application project named "BookEnterpriseApp" with a EJB module "BookEnterpriseApp-ejb"
3) Create a new glassfish JDBC resource on the enterprise app and import the resulting glassfish-resources.xml as a resource on glassfish. Ping successful.
4) Create a new stateless session bean inside BookEnterpriseApp-ejb, called BookEJB while checking checkbox remote in project BookRemote:

package avt.book.ejb;
import avt.book.remoteejb.BookEJBRemote;
import javax.ejb.Stateless;

/@Stateless
public class BookEJB implements BookEJBRemote {

    // Add business logic below. (Right-click in editor and choose
    // "Insert Code > Add Business Method")
}

4) Create the Book Entity.

package avt.book.entity;

import java.io.Serializable;
import javax.persistence.*; // replaced individual classes to save space here

@Entity
@NamedQuery(name = "findAllBooks", query = "SELECT b FROM Book b")
public class Book implements Serializable {
    
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

...
}

I decided to add the Book entity inside the BookRemote project, since it is needed in the interface methods that I need to add:

@Remote
public interface BookEJBRemote {
    Book createBook(Book book);
    void deleteBook(Book book);
}

I did not create a persistence.xml in BookRemote since when I try that I cannot choose the JDBC resource I have added earlier.
This results in warning "project does not contain a persistence unit" on the line @Entity in Book.java.

5) Add a persistence.xml inside BookEnterpriseApp-ejb that refers to the jdbc resource:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="BookEnterpriseApp-ejbPU" transaction-type="JTA">
    <jta-data-source>jdbc/book</jta-data-source>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
      <property name="javax.persistence.schema-generation.database.action" value="create"/>
    </properties>
  </persistence-unit>
</persistence>

6) Create a new Java EE - Enterprise Application Client project named "BookClient", and call BookEJB methods as follows:

package bookclient;
import avt.book.entity.Book;
import avt.book.remoteejb.BookEJBRemote;
import javax.ejb.EJB;

public class Main {

    @EJB
    private static BookEJBRemote bookEJB;

    public static void main(String[] args) {
       // Creates an instance of book
        Book book = new Book();
        book.setTitle("The Hitchhiker's Guide to the Galaxy");
        book = bookEJB.createBook(book);
        System.out.println("### Book created : " + book);     
...

7) Deploy and run the client app.

This results in exceptions:
...
java.lang.reflect.InvocationTargetException
...
Caused by: java.lang.IllegalArgumentException: Object: avt.book.entity.Book[ id=null ] is not a known Entity type.


My Questions:
- Should I indeed add the book entity inside the BookRemote project?
- if yes, what should I change to prevent the execption?

[Frits Walraven]

My Questions:
- Should I indeed add the book entity inside the BookRemote project?
- if yes, what should I change to prevent the execption?  

Yes, you need to add the Remote Interface and all the dependent classes (e.g. superclasses, classes used as method parameters) in the client-jar.

Application client jars are always tough to get it right because it needs a lot of application server dependent configuration. Why don't you try a Servlet? Just have a look at my example (chapter 10) in the EJB 3.1 notes: OCEEJBD-Links.

[Arno van Haastert]

Hi Frits,

Thanks for your quick reply.

I think the next chapter of my book also will go into web applications which probably is a much more common use case than the client application..

In the mean time I somehow managed to make it work by unchecking the "include all entity classes" and adding explicitly the fully qualified Book class in the persistence.xml on BookEnterpriseApp-ejb.
This was suggested in some posts I came across this afternoon but before it resulted in not being able to deploy the BookEnterpriseApp-ejb.

The only thing I can think of doing differently this time is that I initially created the book entity inside BookEnterpriseApp-ejb and then dragged it (refactored it) into the BookClient project.
So still too much hocus-pocus to be completely satisfying but still a happy end of a day of trying ;-)

Next week I might just try once from scratch to see if I can make it work at once.



Regards,

Arno

[Frits Walraven]

Nice! Well done, and thanks for reporting your solution. (have a Cow!)

So still too much hocus-pocus to be completely satisfying but still a happy end of a day of trying ;-)  

Netbeans has some nice wizards and takes a lot of configuration away from the user which can be a pain. My advice is to check after you are finished what classes are in the EAR, WAR or JARs created by Netbeans.