business-interface-pattern

The Problem

EJB component interfaces (Remote/Local) extend EJB-specific interfaces (EJBObject, EJBLocalObject) which have methods meant for clients, not beans. If beans don’t implement the component interface (to avoid pollution), how do we get compile-time checking that the bean has all required business methods?

Core Idea

Define a “pure” business interface containing only your business method signatures—no EJB dependencies. Have both the Remote/Local interface AND the bean class implement this business interface. This gives compile-time checking without polluting the bean with EJB client methods.

How It Works

// 1. Pure business interface (no EJB stuff)
public interface HelloBusinessMethods {
    String hello() throws RemoteException;
}
 
// 2. Remote interface extends BOTH EJBObject and business interface
public interface HelloRemote extends javax.ejb.EJBObject, HelloBusinessMethods {}
 
// 3. Local interface also extends business interface
public interface HelloLocal extends javax.ejb.EJBLocalObject, HelloBusinessMethods {}
 
// 4. Bean implements business interface (+ SessionBean)
public class HelloBean implements SessionBean, HelloBusinessMethods {
    public String hello() { return "Hello, World!"; }
}

Visual Explanation

Key Properties

Compile-time safety: If bean misses a business method, compilation fails
No pollution: Bean doesn’t implement EJBObject methods
Shared contract: Both bean and EJB object share the same business method signatures
One downside: Local interface inherits RemoteException from business interface (if business interface declares it)

Semantic Network

graph semantic__Business_Interface_Pattern_ {
  layout=neato
  node [shape=ellipse fontname="Helvetica" fontsize=11 style=filled]
  THIS [label=""Business Interface " fillcolor="#ffd700" fontsize=13 style="filled,bold"]
  REL1 [label="Related Concept" fillcolor="#f0f0f0"]
  REL2 [label="Builds Into" fillcolor="#d4edda"]
  THIS -- REL1 [label="related"]
  THIS -- REL2 [label="builds into"]
}

Connections

Built from: Why Bean Doesn't Implement Component Interface
Builds into: Remote Interface, Local Home Interface
Related: Session Bean, Entity Bean
Contrasts with: Direct implementation (bean implements remote interface directly)

Edge Cases & Gotchas

RemoteException leakage: Business interface meant for both remote and local still declares RemoteException—local clients don’t need it
EJB 3.x+ solves this: Uses @Local and @Remote annotations—no need for this pattern
Not mandatory: Most developers just let the container verify at deployment time (not compile time)

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