学步园

Service Locator如下：

package com.jdon.servicelocator.web;


import java.util.HashMap;
import java.util.Map;
import java.util.Collections;
import java.net.URL;


import javax.ejb.EJBHome;
import javax.ejb.EJBLocalHome;
import javax.jms.QueueConnectionFactory;
import javax.jms.Queue;
import javax.jms.TopicConnectionFactory;
import javax.jms.Topic;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.rmi.PortableRemoteObject;
import javax.sql.DataSource;

import com.jdon.servicelocator.ServiceLocatorException;

/**
 * This class is an implementation of the Service Locator pattern. It is
 * used to looukup resources such as EJBHomes, JMS Destinations, etc.
 * This implementation uses the "singleton" strategy and also the "caching"
 * strategy.
 * This implementation is intended to be used on the web tier and
 * not on the EJB tier.
 */
public class ServiceLocator {

private InitialContext ic;
private Map cache; //used to hold references to EJBHomes/JMS Resources for re-use

private static ServiceLocator me;

static {
try {
        me = new ServiceLocator();
      } catch(ServiceLocatorException se) {
        System.err.println(se);
        se.printStackTrace(System.err);
      }
    }

private ServiceLocator() throws ServiceLocatorException  {
try {
        ic = new InitialContext();
cache = Collections.synchronizedMap(new HashMap());
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
       }
    }

static public ServiceLocator getInstance() {
return me;
    }






/**
     * will get the EJB Local home factory. If this EJB home factory has already been
     * clients need to cast to the type of EJBHome they desire
     *
     * @return the EJB Home corresponding to the homeName
     */
public EJBLocalHome getLocalHome(String jndiHomeName) throws ServiceLocatorException {
EJBLocalHome home = null;
try {
if (cache.containsKey(jndiHomeName)) {
            home = (EJBLocalHome) cache.get(jndiHomeName);
        } else {
            home = (EJBLocalHome) ic.lookup(jndiHomeName);
cache.put(jndiHomeName, home);
        }
       } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
       } catch (Exception e) {
throw new ServiceLocatorException(e);
       }
return home;
    }

/**
     * will get the EJB Remote home factory. If this EJB home factory has already been
     * clients need to cast to the type of EJBHome they desire
     *
     * @return the EJB Home corresponding to the homeName
     */
public EJBHome getRemoteHome(String jndiHomeName, Class className) throws ServiceLocatorException {
EJBHome home = null;
try {
if (cache.containsKey(jndiHomeName)) {
            home = (EJBHome) cache.get(jndiHomeName);
        } else {
            Object objref = ic.lookup(jndiHomeName);
            Object obj = PortableRemoteObject.narrow(objref, className);
            home = (EJBHome)obj;
cache.put(jndiHomeName, home);
        }
       } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
       } catch (Exception e) {
throw new ServiceLocatorException(e);
       }

return home;
    }


/**
     * @return the factory for the factory to get queue connections from
     */
public  QueueConnectionFactory getQueueConnectionFactory(String qConnFactoryName)
                                                 throws ServiceLocatorException {
      QueueConnectionFactory factory = null;
try {
if (cache.containsKey(qConnFactoryName)) {
            factory = (QueueConnectionFactory) cache.get(qConnFactoryName);
        } else {
            factory = (QueueConnectionFactory) ic.lookup(qConnFactoryName);
cache.put(qConnFactoryName, factory);
        }
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return factory;
    }


/**
     * @return the Queue Destination to send messages to
     */
public  Queue getQueue(String queueName) throws ServiceLocatorException {
      Queue queue = null;
try {
if (cache.containsKey(queueName)) {
            queue = (Queue) cache.get(queueName);
        } else {
            queue =(Queue)ic.lookup(queueName);
cache.put(queueName, queue);
        }
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }

return queue;
    }


/**
     * This method helps in obtaining the topic factory
     * @return the factory for the factory to get topic connections from
     */
public  TopicConnectionFactory getTopicConnectionFactory(String topicConnFactoryName) throws ServiceLocatorException {
      TopicConnectionFactory factory = null;
try {
if (cache.containsKey(topicConnFactoryName)) {
            factory = (TopicConnectionFactory) cache.get(topicConnFactoryName);
        } else {
            factory = (TopicConnectionFactory) ic.lookup(topicConnFactoryName);
cache.put(topicConnFactoryName, factory);
        }
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return factory;
    }

/**
     * This method obtains the topc itself for a caller
     * @return the Topic Destination to send messages to
     */
public  Topic getTopic(String topicName) throws ServiceLocatorException {
      Topic topic = null;
try {
if (cache.containsKey(topicName)) {
            topic = (Topic) cache.get(topicName);
        } else {
            topic = (Topic)ic.lookup(topicName);
cache.put(topicName, topic);
        }
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return topic;
    }

/**
     * This method obtains the datasource itself for a caller
     * @return the DataSource corresponding to the name parameter
     */
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(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return dataSource;
    }

/**
     * @return the URL value corresponding
     * to the env entry name.
     */
public URL getUrl(String envName) throws ServiceLocatorException {
      URL url = null;
try {
        url = (URL)ic.lookup(envName);
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }

return url;
    }

/**
     * @return the boolean value corresponding
     * to the env entry such as SEND_CONFIRMATION_MAIL property.
     */
public boolean getBoolean(String envName) throws ServiceLocatorException {
      Boolean bool = null;
try {
        bool = (Boolean)ic.lookup(envName);
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return bool.booleanValue();
    }

/**
     * @return the String value corresponding
     * to the env entry name.
     */
public String getString(String envName) throws ServiceLocatorException {
      String envEntry = null;
try {
        envEntry = (String)ic.lookup(envName);
      } catch (NamingException ne) {
throw new ServiceLocatorException(ne);
      } catch (Exception e) {
throw new ServiceLocatorException(e);
      }
return envEntry ;
    }

}