Need help on EJB2.0 Local interfaces

[Joshua Masuki]

Hi,

By mistake, I have posted this message in SCWCD thread. I'm just creating a copy here. I need help on local interfaces.

Thank you.

------
Hello there,

I am new to EJB and I am trying out Local home and component interfaces. According to the book that I have read, for one EJB, you can expose both local and remote home/component interfaces. Does this mean we would only have one JNDI for this EJB? Whether the local or remote interfaces will be used, will depend if you narrow or downcast? (Please see below code)

InitialContext ic = new InitialContext();
Object o = ic.lookup("JNDI_Name"); 
 
MyRemoteHome home = (MyRemoteHome) 
      PortableRemoteObject.narrow(obj, MyRemoteHome .class);
--- or ---
MyLocalHome home = (MyLocalHome) o;

But when I do the second one (ordinary type cast) from another EJB to get my bean's local home, I encounter a ClassCastException. What could have gone wrong?

Thank you for your help.

J.M.
SCJP2

[Keerthi P]

This is really confusing for most of us as the book does not cover it in good detail.

Does this mean we would only have one JNDI for this EJB?

Yes. Even if your bean has both local and remote interfaces, there will be only one JNDI name.

Whether the local or remote interfaces will be used, will depend if you narrow or downcast?

Not exactly. To get the local interface of an EJB, you need to have the ejb-local-ref element defined in the deployment descriptor. This element will map the JNDI name you use to lookup to the actual bean name.

For instance,
If Bean B needs Bean A's local interface, Bean B should define ejb-local-ref in its deployment descriptor.

To get the remote interface of an ejb, you need to have ejb-ref element defined in your deployment descriptor.

Example:

  
<session>
<ejb-name>Bean B</ejb-name>
...

<ejb-local-ref>
<ejb-ref-name>BeanALocalRef</ejb-ref-name>
...
<ejb-link>Bean A</ejb-link>
</ejb-local-ref>
 
<ejb-ref>
<ejb-ref-name>BeanARemoteRef</ejb-ref-name>
...
<ejb-link>Bean A</ejb-link>
</ejb-ref>

</session>
 
<session>
<ejb-name>Bean A</ejb-name>
...
</session>

To lookup remote interface, use jndi.lookup("java:comp/env/BeanARemoteRef") and then narrow the stub to get the remote home object.

To lookup local interface, use jndi.lookup("java:comp/env/BeanALocalRef") and then type cast the object returned to get the local home object.

[Joshua Masuki]

Hi Keerthi,

Thanks so much for the help. I'll it out and hopefully this works for me this time.

- JM

[Joshua Masuki]

Hi,

It seems not to be working on my end. I still encounter ClassCastException. Can somebody please help?

In this example of mine, the client uses PermutationBean (my 1st bean), which uses FactorialBean (my 2nd bean). MyPermutation and MyFactorial are JNDI names for PermutationBean and FactorialBean, respectively.

Here is my DD:

<ejb-jar>
  <display-name>MathJar</display-name>
  <enterprise-beans>
    <session>
      <display-name>FactorialBean</display-name>
      <ejb-name>FactorialBean</ejb-name>
      <home>practice.stateless.FactorialHomeRemote</home>
      <remote>practice.stateless.FactorialRemote</remote>
      <local-home>practice.stateless.FactorialHomeLocal</local-home>
      <local>practice.stateless.FactorialLocal</local>
      <ejb-class>practice.stateless.FactorialBean</ejb-class>
      <session-type>Stateless</session-type>
      <transaction-type>Bean</transaction-type>
      <security-identity>
        <description></description>
        <use-caller-identity></use-caller-identity>
      </security-identity>
    </session>
    <session>
      <display-name>PermutationBean</display-name>
      <ejb-name>PermutationBean</ejb-name>
      <home>practice.stateless.PermutationHomeRemote</home>
      <remote>practice.stateless.PermutationRemote</remote>
      <ejb-class>practice.stateless.PermutationBean</ejb-class>
      <session-type>Stateless</session-type>
      <transaction-type>Bean</transaction-type>
      <ejb-local-ref>
        <ejb-ref-name>FactorialBean</ejb-ref-name>
        <ejb-ref-type>Session</ejb-ref-type>
        <local-home>practice.stateless.FactorialHomeLocal</local-home>
        <local>practice.stateless.FactorialLocal</local>
        <ejb-link>FactorialBean</ejb-link>
      </ejb-local-ref>
      <security-identity>
        <description></description>
        <use-caller-identity></use-caller-identity>
      </security-identity>
    </session>
  </enterprise-beans>
</ejb-jar>

Here is a code snippet of my first EJB, PermutationBean:

// business method permutation
public float permutation(int n, int r) {
    //return factorial(n)/factorial(n-r);
    float result = 3;
    try {
        InitialContext ctx = new InitialContext();
 
        Object obj = ctx.lookup("MyFactorial");
        FactorialHomeLocal home = (FactorialHomeLocal) obj;
        FactorialLocal bean = home.create();
        result = bean.factorial(n);
    } (Exception e) {
        // In my actual code, NamingException, CreateException, 
        // MathException were in the try-catch block
    }
}        

And here's the code snippet of my client:

try {
    InitialContext ctx = new InitialContext();
    Object obj = ctx.lookup("MyPermutation");
    PermutationHomeRemote home = (PermutationHomeRemote)
        PortableRemoteObject.narrow(obj, 
                PermutationHomeRemote.class);
    PermutationRemote bean = home.create();
    float result = bean.permutation(5,2);
    System.out.println("Permutation: " + result);
} catch (Exception e) {
    // In my actual code, NamingException, CreateException,
    // MathException, RemoteException were in thetry-catch block
}

Thank you very much.

- JM
[ February 28, 2005: Message edited by: Joshua Masuki ]

[Keerthi P]

Change Object obj = ctx.lookup("MyFactorial"); to Object obj = ctx.lookup("java:comp/env/MyFactorial");

It should work.

[Keerthi P]

ctx.lookup("MyFactorial") tries to look up the remote home that is not type compatible with your client code. Your client code gets the stub of remote which is why you get ClassCastException.

[Joshua Masuki]

Hi,

Apparently, using Object obj = ctx.lookup("java:comp/env/MyFactorial") does not work, I got NamingException. My JNDI name for FactorialBean is "MyFactorial", so I don't think "java:comp/env/MyFactorial" would work.

What do you think is other cause of problem? How can I make this work?

Thank you so much!

- JM

[Keerthi P]

OK. My mistake. I did not read the ref-name properly from you DD.

<ejb-local-ref>
<ejb-ref-name>FactorialBean</ejb-ref-name>
<ejb-ref-type>Session</ejb-ref-type>
<local-home>practice.stateless.FactorialHomeLocal</local-home>
<local>practice.stateless.FactorialLocal</local>
<ejb-link>FactorialBean</ejb-link>
</ejb-local-ref>

You should use the ejb-ref-name in your lookup code. Use "java:comp/env/FactorialBean".

[Joshua Masuki]

Hi,

It's working now. Thank you so much!

- JM

[amol deshpande]

hi,

for accessing other bean from bean,
"java:comp/env/ejb/BeanName" should be JNDI context.
"java:comp/env/" is context for enviroment entities.

whatever you have in java:come/env is not a home interface for your bean and heance your getting ClassCastException.
Amol.