Monday, September 29, 2008

Invoking EJB deployed on a remote machine



Invoking EJB deployed on a remote machine

In case we are calling remote ejb( ejb deployed on remote machines),
The JNDI lookup might lookup like,

Properties env = new Properties();
  env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");
  env.put(Context.PROVIDER_URL, "10.227.16.72:1099");  
  env.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces"); 
  Context ctx = new InitialContext(env);

If we are calling local ejb then we can simply create InitialContext without any parameters.

Like,
Context ctx = new InitialContext();


Using ENC JNDI to access EJBs 

IF we want to use ENC JNDI then the , in the lookup method the name of the JNDI passed is prefixed with java:comp/env/ so, if we wish to use ENC JNDI and access ejb Sidd
The JNDI name will look like java:comp/env/ejb/Fibo.

It is a good practice to use ENC JNDI, since it seperates configuration from coding. In case of ENC JNDI we have to put the entries in web.xml and jboss-web.xml



Reasons to USE ENC(Environment Naming Context:: java:comp/env) JNDI 

Some of the reasons why ENC JNDI is advocated ,

1) You can easily change Datasource, EJB without code modification.

For example:
1)- you want to change datasource for your application, thanks to ENC JNDI you
can do it without modifing code and recompiling, just edit xml file,

2) - you can write complete EJB and test it without complete design of whole
application (you don't have to know exact JNDI name of EJB),

 3) - It's easy to write GUI application for configuring J2EE applications -
everything is in XML files not in code.

4) Someone else writes the code and someone else configures. "Application
Assembler" and "Application Deployer and Administrator" theoretically even
don't have to know java.


Pseudo Code to get Home interface of and EJB using ENC JNDI


Context ctx = new InitialContext();
Object narrowFromObj = ctx.lookup(remoteHomeJndiName);
 remoteHome = (EJBHome) PortableRemoteObject.narrow(narrowFromObj,ejbRemoteHomeClass); 

where remoteHomeJndiName="java:comp/env/" +EJB_REF_NAME;

where EJB_REF_NAME is the <ejb-ref-name> EJB_REF_NAME </ejb-ref-name> defined in side web.xml





Lookup an EJB from a different application, deployed on the same server, in JBoss

In the web.xml of your war(the web application through which you want to access the EJB), have the following entry:
<ejb-ref>
  <ejb-ref-name>GiveAnyNameByWhichYouWouldLikeToReferTheBeanInYourWebApp</ejb-ref-name>
  <ejb-ref-type>session</ejb-ref-type>
  <home>packageName.ClassNameOfTheHomeObjectOfTheBeanYouWantToRefer
</home>
  <remote>packageName.ClassNameOfTheRemoteObjectOfTheBeanYouWantToRefer</remote>
  </ejb-ref>
 
  In the jboss-web.xml of your war, have the following entry:
 
  <ejb-ref>
  <ejb-ref-name>GiveAnyNameByWhichYouWouldLikeToReferTheBeanInYourWebApp(This should be same as the one given in the web.xml above)
</ejb-ref-name>
  <jndi-name>TheJndiNametoWhichTheBeanIsBound(Example:somecontext/somejndiName)YouWillFindThisJndiNameInTheJboss.xmlOfTheEJB</jndi-name>
  </ejb-ref>
  In your code, do the lookup as:
 
  Context ic = new InitialContext();
  Object ejbHome = ic.lookup("java:comp/env/TheNameThatYouHadGivenInTheEJB-REF-NAMETagOfJbossWeb.xmlAbove");
Here's an example:
web.xml:
<ejb-ref>
  <ejb-ref-name>MyTestBean</ejb-ref-name>
  <ejb-ref-type>session</ejb-ref-type>
  <home>com.test.ejb.MyBeanHome</home>
  <remote>com.test.ejb.MyBeanRemote</remote>
  </ejb-ref>
jboss-web.xml:
 <ejb-ref>
  <ejb-ref-name>MyTestBean</ejb-ref-name>
  <jndi-name>myejb/test/MyTestBean</jndi-name>
 </ejb-ref>
 
Lookup code:
Context ic = new InitialContext();
  Object ejbHome = ic.lookup("java:comp/env/MyTestBean");



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