Server-side Java: Create forward-compatible beans in EJB, Part 2

public class AccountBean implements EntityBean {
  int id;
  double balance;
  String modifiedBy;
  EntityContext ejbContext;
  PortableContext portableContext;
  public void withdraw(Double withdraw)
      throws WithdrawLimitException, AccessDeniedException {
    // only tellers can withdraw more than 10k
    if(withdraw.doubleValue() > 10000) {
      Identity tellerIdnty = new RoleIdentity("teller");
      boolean isTeller = ejbContext.isCallerInRole(tellerIdnty)
      if(!isTeller)
        throw new AccessDeniedException();
    }
    Double limit = (Double)
      portableContext.getEnvironmentEntry(
        "java:comp/env/withdraw_limit", Double.class);
    if (withdraw.doubleValue() > limit.doubleValue())
      throw new WithdrawLimitException(limit);
    else
      balance = balance - withdraw.doubleValue();
    Identity identity = ejbContext.getCallerIdentity( );
    String modifiedBy = identity.getName();
  }
  ...
}

public class AccountBean implements EntityBean {
  int id;
  double balance;
  String modifiedBy;
  EntityContext ejbContext;
  PortableContext portableContext;
  public void withdraw(Double withdraw)
      throws WithdrawLimitException, AccessDeniedException {
    // only tellers can withdraw more than 10k
    if(withdraw.doubleValue() > 10000) {
      boolean isTeller = ejbContext.isCallerInRole("teller")
      if (!isTeller)
        throw new AccessDeniedException( );
    }
    Double limit = (Double)
      portableContext.getEnvironmentEntry(
        "java:comp/env/withdraw_limit",Double.class);
    if (withdraw.doubleValue() > limit.doubleValue())
      throw new WithdrawLimitException(limit);
    else
      balance = balance - withdraw.doubleValue();
    Principal principal = ejbContext.getCallerPrincipal( );
    String modifiedBy = principal.getName();
  }
  ...
}

import javax.ejb.*;
import java.lang.reflect.Method;
import java.security.Principal;

public abstract class PortableContext {
    final static String SYSTEM_PROPERTY_NAME = "java.ejb.portable_context";
    
    EJBContext ejbContext;
    
    public static PortableContext getInstance(EJBContext context) 
    throws PortableContextException{
             
        String className = System.getProperty(SYSTEM_PROPERTY_NAME);
        if(className == null)
            throw new PortableContextException("System property for implementation not set");
        try{
            Class clazz = Class.forName(className);
            PortableContext portableCtx = (PortableContext)clazz.newInstance();
            portableCtx.setEJBContext(context);
            return portableCtx;
        }catch(Exception e){
            throw new PortableContextException(e);
        }
    }
   
    public void setEJBContext(EJBContext ctx){
        ejbContext = ctx;
    }
    public abstract Object lookup(String name, Class type)throws PortableContextException;

    public abstract Principal getCallerPrincipal( );

    public abstract boolean isCallerInRole(String roleName);
}