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"Distributed Logging Using The Java Messsage Service, by David Chappell & Greg Pavlik"
Vol. 6, Issue 5, p. 90

	


Listing 1: Interface for the logging client to send messages to a log service 
  
package util.log; 
/** 
 * Title: ClientLog 
 * Description: Interface defining the logging API used by 
   logging clients. 
 * @author Greg Pavlik 
 * @author David Chappell 
 */ 
public interface ClientLog 
{ 
  public void logMessage(String message) throws LogException; 
} 
  
  

Listing 2: The JMS-based implementation of the 

ClientLog interface package util.log;
import javax.jms.*; /** * Title: JMSClientLogImpl * Description: Implementation of logging service logging client API; uses JMS * to send the application log. * @author Greg Pavlik * @author David Chappell */ public class JMSClientLogImpl implements ClientLog { /** queue sender for connection */ private QueueSender m_sender = null; /** queue session for connection */ private QueueSession m_session = null; /** * No arg constructor for log service implementation. * Acquire a reference to administered queue via standard * JNDI lookups. * @param initialContextFactory initial context factory * @exception thrown if constructor cannot initialize queue sender */ public JMSClientLogImpl(String initialContextFactory) throws LogException { try { //acquire JMS queue reference via JNDI java.util.Hashtable env = new java.util.Hashtable(); env.put(javax.naming.Context.INITIAL_CONTEXT_FACTORY, initialContextFactory); javax.naming.InitialContext context = new javax.naming.InitialContext(env); QueueConnectionFactory qcf = (QueueConnectionFactory) context.lookup("QueueConnectionFactory"); QueueConnection connection = qcf.createQueueConnection(); QueueSession session = connection.createQueueSession (false, QueueSession.AUTO_ACKNOWLEDGE); Queue queue = (Queue)context.lookup("LogQueue"); m_sender = session.createSender(queue); } catch (Exception e) { throw new LogException(e.getMessage()); } } /** * Takes an input string and pushes message on to log queue * @param logEntry the input String */ public void logMessage(String logEntry) throws LogException { try { TextMessage message = m_session.createTextMessage(); message.setText(logEntry); m_sender.send(message); } catch (Exception e) { throw new LogException(e.getMessage()); } } } Listing 3: A factory class for the implementation of the
ClientLog interface package util.log;
/** * Title: ClientLogFactory * Description: Acts as a factory maintaining implementation of ClientLog as a singleton instance. * @author Greg Pavlik * @author David Chappell */ public class ClientLogFactory { /** client log implementation returned by factory */ static private ClientLog m_logImpl = null; static { //hard code for example m_logImpl = new JMSClientLogImpl("JMS Initial Context Factory"); } /** * provides access to singleton instance * @return implementation of ClientLog interface */ static public ClientLog instance() throws LogException { return m_logImpl; } } Listing 4: A message listener that sends text to standard error on
monitoring console package util.log;
/** * Title: LogServiceMessageListener * Description: Message Listener for distributed log example. This example extracts the message text from the message and writes it to standard err. * @author Greg Pavlik * @author David Chappell */ import javax.jms.MessageListener; import javax.jms.Message; import javax.jms.TextMessage; public class LogServiceMessageListener implements MessageListener { /** * Send message contents to standard error * @param message the text message sent from */ public void onMessage(Message message) { try { String text = ((TextMessage)message).getText(); System.err.println(text); } catch(Exception e) { System.err.println("SYSTEM ERROR: could not process message: " + message); } } } Listing 5: A tag extension for JSPs package util.log; /** * Title: LogClientTag * Description: A tag extension for JSPs that uses the ClientLog implementation. * This can be used to send log messages to the JMS queue without * writing any Java code. * @author Greg Pavlik * @author David Chappell */ import javax.servlet.jsp.tagext.TagSupport; public class LogClientTag extends TagSupport { /** Client log message set by JSP engine during tag processing*/ private String m_message = null; /** no arg constructor */ public LogClientTag() { ; } /** * After tag has been encountered, simply send text to ClientLog */ public int doEndTag() throws javax.servlet.jsp.JspException { try { ClientLogFactory.instance().logMessage(m_message); return javax.servlet.jsp.tagext.Tag.SKIP_BODY; } catch (LogException e) { throw new javax.servlet.jsp.JspException(e.getMessage()); } } //ATTRIBUTE ACCESSOR/MUTATORS public void setMessage(String value) { m_message = value; } public String getMessage() { return m_message; } }
 

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