Here's an update on the logger issue. It too me long to figure out because I
ran into an issue about privileged servlets and had to write my own
log4j.properties parser.
The original code posted earlier in this thread works in that it creates a
different logger for web application, and allows the user to stop and restart
the application.
public static Logger getLogger()
{
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
URL log4j_properties = classLoader.getResource("log4j_app.properties");
String loggerName = log4j_properties.toString(); // throws
NullPointerException if log4j_app.properties does not exist
synchronized (MyLog.class)
{
Logger logger =
Logger.getRootLogger().getLoggerRepository().exists(loggerName);
if (logger == null)
{
logger = Logger.getLogger(loggerName);
PropertyConfigurator.configure(log4j_properties);
System.out.println("Created logger: loggerName=" + loggerName);
}
return logger;
}
}
One bug with the above is the line
PropertyConfigurator.configure(log4j_properties);
The above re-configures the root logger with the new log4j.properties, so
basically the new configuration applies to all loggers. What would be nice is
PropertyConfigurator.configure(logger, log4j_properties);
that configures only the specified logger with the log4j_properties.
Unfortunately, log4j does not have such a function, so I wrote my own (but it
only supports the properties used in my log4j_app.properties files).
Now, if web application 1 calls MyLog.getLogger() or calls common code that
calls MyLog.getLogger() then the first logger will be used, and similarly for
web application 2.
Finally, I create a servlet
import org.apache.catalina.manager.ManagerServlet;
public class TomcatManagerServlet extends ManagerServlet
The servlet is called for "/reload", and it calls super.doGet() after doing
some checks.
It turns out that only privileged web applications can instantiate
ManagerServlet, so one has to have the following in context.xml:
<Context privileged="true">
I'm not sure what is the practical impact of setting privileged="true", though
the docs said something about the catalina and shared class loaders.
So upon calling
http://localhost/mywebservice/reload?path=/
the ROOT application is stopped and started. After the application restart,
all users are logged out and they have to log in again, but the logger
continues to work. A call to MyLog.getLogger() does not re-create the logger.
The logger is really owned by the common code in ${catalina.home}/lib. The
code
URL log4j_properties = classLoader.getResource("log4j_app.properties");
just gets the URL of the log4j.properties file. However, there is no pointer
to anything in the webapp, so it's possible to stop the webapp. And the line
PropertyConfigurator.configure(log4j_properties);
opens the URL (by calling log4j_properties.getInputStream()), reads it, and
closes it. So no stream in the webapp is open, and it's possible to stop the
webapp.
--- On Thu, 1/15/09, Caldarale, Charles R <chuck.caldar...@unisys.com> wrote:
> From: Caldarale, Charles R <chuck.caldar...@unisys.com>
> Subject: RE: How to have multiple loggers with shared code also using the
> logger?
> To: "Tomcat Users List" <users@tomcat.apache.org>
> Date: Thursday, January 15, 2009, 11:28 AM
> > From: removeps-gro...@yahoo.com
> [mailto:removeps-gro...@yahoo.com]
> > Subject: RE: How to have multiple loggers with shared
> code
> > also using the logger?
> >
> > How does one redploy a single application? Strange, I
> > could not find any information on this seemingly basic
> > task on google.
>
> Read the real docs first, then Google only if needed.
> http://tomcat.apache.org/tomcat-6.0-doc/deployer-howto.html#Deploying%20on%20a%20running%20Tomcat%20server
> http://tomcat.apache.org/tomcat-6.0-doc/manager-howto.html
>
> - Chuck
>
>
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