Question

I have an application which consists of message driven bean and a couple of session beans. One of them has a DAO object, that is responsible for accessing database or FTP server.

I need to have two applications. The only difference between them is the instance of DAO class. Can I specify that instance during the deployment phase?

My purpose is to avoid code duplication.

Answer 1

If the DAO is just a POJO, then I would suggest a Class env-entry if you’re using EE6 (or a String env-entry if you’re not, and then do the Class.forName yourself):

<env-entry>
  <env-entry-name>daoClass</env-entry-name>
  <env-entry-type>java.lang.Class</env-entry-type>
  <!-- Specify a default, override at deployment time. -->
  <env-entry-value>com.example.project.DefaultDAO</env-entry-value>
</env-entry>

@Resource(name="daoClass")
private void setDAOClass(Class<com.example.project.DAO> daoClass) {
    this.dao = daoClass.newInstance();
}

Alternatively, if your DAO implementation were an EJB, then you could use @EJB injection, and specify the binding name at deployment time.