Example 8.34 Implementing Type Checked Service Locator Strategy

package corepatterns.apps.psa.util;
// imports
...
public class ServiceLocator {
  // singleton's private instance 
  private static ServiceLocator me;
  
  static {
    me = new ServiceLocator();
  }
    
  private ServiceLocator() {}

  // returns the Service Locator instance 
  static public ServiceLocator getInstance() { 
    return me;
  }

  
  // Services Constants Inner Class - service objects
  public class Services {
    final public static int PROJECT  = 0;
    final public static int RESOURCE = 1;
  }    

  // Project EJB related constants
  final static Class  PROJECT_CLASS = ProjectHome.class;                      
  final static String PROJECT_NAME  = "Project";

  // Resource EJB related constants
  
  final static Class  RESOURCE_CLASS = ResourceHome.class;                        
  final static String RESOURCE_NAME  = "Resource";

  // Returns the Class for the required service 
  static private Class getServiceClass(int service){
    switch( service ) {
      case Services.PROJECT:
        return PROJECT_CLASS;
      case Services.RESOURCE:
      return RESOURCE_CLASS;
    }
    return null;
  }
    
  // returns the JNDI name for the required service 
  static private String getServiceName(int service){
    switch( service ) {
      case Services.PROJECT:
        return PROJECT_NAME;
      case Services.RESOURCE:
        return RESOURCE_NAME;
    }
    return null;
  }
    
  /* gets the EJBHome for the given service using the 
  ** JNDI name and the Class for the EJBHome
  */
  public EJBHome getHome( int s ) 
    throws ServiceLocatorException {
    EJBHome home = null;
    try {
        Context initial  = new InitialContext();

      // Look up using the service name from 
      // defined constant
      Object objref = 
        initial.lookup(getServiceName(s));

      // Narrow using the EJBHome Class from 
      // defined constant
      Object obj = PortableRemoteObject.narrow( 
                objref, getServiceClass(s));
      home = (EJBHome)obj;
    }
    catch( NamingException ex ) {
        throw new ServiceLocatorException(...);
    }
    catch( Exception ex ) {
        throw new ServiceLocatorException(...);
    }
    return home;
  }
}