ejbhomefactory.java

J2EE 1.4程序设计教程图书配套的源代码

package com.ibm.ejb;
import java.util.Map;
import javax.ejb.EJBHome;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
public class EJBHomeFactory {
      private static EJBHomeFactory;
      private Map homeInterfaces;
      private Context context;
      // This is private， and can't be instantiated directly
      private EJBHomeFactory() throws NamingException {
          homeInterfaces = new HashMap();
          // Get the context for caching purposes
          context = new InitialContext();
          /**
           * In non-J2EE applications， you might need to load up
           *   a properties file and get this context manually. I've
           *   kept this simple for demonstration purposes.
           */
      }
      public static EJBHomeFactory getInstance() throws NamingException {
          // Not completely thread-safe， but good enough 
          // (see note in article)
          if (instance == null) {
              instance = new EJBHomeFactory();
          }
          return instance;
      }
      public EJBHome lookup(String jndiName， Class homeInterfaceClass) 
            throws NamingException {
          // 查看是否缓存了这个接口
          EJBHome homeInterface = (EJBHome)homeInterfaces.get(homeClass);
          // 如果没有的话，则使用给出的JNDI名字进行查找
          if (homeInterface == null) {
              Object obj = context.lookup(jndiName);
              homeInterface =
               (EJBHome)PortableRemoteObject.narrow(obj， homeInterfaceClass);
              // If this is a new ref， save for caching purposes
              homeInterfaces.put(homeInterfaceClass， homeInterface);
          }
          return homeInterface;
      }
}