servicelocator.java

我在加拿大学习的一个比较复杂的在线银行程序.

package com.ebusiness.ebank.servicedelegate;

/**
 * <p>Title: </p>
 * <p>Description: This class provides the center service for possible JNDI lookup
 *                  and stores the objects that is successfully located into HashMap for re-use
 *
 *                  It might be used by remote clients, so avoid using log4j</p>
 * <p>Copyright: Copyright (c) 2005</p>
 * <p>Company: eBusiness Inc., All right reserved</p>
 * @author unascribed
 * @version 1.0
 */

import java.util.HashMap;
import java.util.Map;
import java.util.Collections;
import javax.ejb.EJBHome;
import javax.ejb.EJBLocalHome;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.rmi.PortableRemoteObject;
import javax.sql.DataSource;

import com.ebusiness.ebank.exception.ErrorMessages;

public class ServiceLocator
{
    private InitialContext ic;
    private Map cache; //used to hold references to Resources for re-use

    private static ServiceLocator me;

    static
    {
        me = new ServiceLocator();
    }

    private ServiceLocator()
    {
        try
        {
            ic = new InitialContext();
            cache = Collections.synchronizedMap(new HashMap());
            System.out.println("\nServiceLocator was successfully instantiated.");
        }
        catch (NamingException ne)
        {
            System.out.println("\n" + ErrorMessages.FAIL_TO_INSTANTIATE_SERVICELOCATOR);
        }
    }

    public static ServiceLocator getInstance()
    {
        return me;
    }

    //After calling this method, you should cast EJBLocalHome to your concrete local home object
    public EJBLocalHome getLocalHome(String localHomeName) throws ServiceLocatorException
    {
        EJBLocalHome home = null;
        try
        {
            if (cache.containsKey(localHomeName))
            {
                home = (EJBLocalHome) cache.get(localHomeName);
            }
            else
            {
                home = (EJBLocalHome) ic.lookup(localHomeName);
                cache.put(localHomeName, home);
            }
        }
        catch (NamingException ne)
        {
            cache.put(localHomeName, null);

            //The codes usually try local home first. If it fails, then try remote home.
            throw new ServiceLocatorException(ErrorMessages.FAIL_TO_LOOKUP_LOCALHOME + ": " + localHomeName + ".", ne);
        }
        return home;
    }

    //After calling this method, you should cast EJBHome to your concrete remote home object
    public EJBHome getRemoteHome(String remoteHomeName, Class className) throws ServiceLocatorException
    {
        EJBHome home = null;
        try
        {
            if (cache.containsKey(remoteHomeName))
            {
                home = (EJBHome) cache.get(remoteHomeName);
            }
            else
            {
                Object objref = ic.lookup(remoteHomeName);
                Object obj = PortableRemoteObject.narrow(objref, className);
                home = (EJBHome)obj;
                cache.put(remoteHomeName, home);
            }
        }
        catch (NamingException ne)
        {
            throw new ServiceLocatorException(ErrorMessages.FAIL_TO_LOOKUP_REMOTEHOME + ": " + remoteHomeName + ". ", ne);
        }
        return home;
    }

    public DataSource getDataSource(String dataSourceName) throws ServiceLocatorException
    {
        DataSource dataSource = null;
        try
        {
            if (cache.containsKey(dataSourceName))
            {
                dataSource = (DataSource) cache.get(dataSourceName);
            }
            else
            {
                dataSource = (DataSource)ic.lookup(dataSourceName);
                cache.put(dataSourceName, dataSource );
            }
        }
        catch (NamingException ne)
        {
            throw new ServiceLocatorException(ErrorMessages.FAIL_TO_LOOKUP_DATASOURCE + ": " + dataSourceName + ". ", ne);
        }
        return dataSource;
    }
}