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From Rick Hillegas <rick.hille...@oracle.com>
Subject Re: Is there some way an external class can find where derby.system.home points to
Date Mon, 09 Sep 2013 13:29:53 GMT
On 9/6/13 5:35 AM, Bergquist, Brett wrote:
> I finally broke down and wrote RollingFileStream which provides (and borrows) most of
the functionality of java.logger.FileHandler to provide a rolling file stream.   Having derby.log
grow forever on long running systems is just not acceptable anymore ;)   Realistically, I
would like to provide this back to the derby community somehow as I found many requests for
such a feature while searching and many references to using "derby.stream.error.method" or
"derby.stream.error.field", but no good implementation of such.
> I built a DerbyUtil.jar which the class along with a configurator class which can read
a "derbylog.properties" file for configuration information.   I would like to locate this
file at the same place as "derby.properties" so the configurator needs to find out what "derby.system.home"
is set to.   Because of the default security policy installed by the network server and because
my DerbyUtil.jar is separate, it cannot access the property.   Create and installing my own
security policy is also a bit of a pain as the network server is started by Glassfish and
there really is not much opportunity to pass startup parameters.
> So is there someway to locate the location that  "derby.ssystem.home" is pointing to
in my class that is being invoke by "derby.stream.error.field"?
> How about a proposal that "derby.stream.error.field" can point to a static method that
can take 0 or 1 parameters and if one parameter, it is passed the value of "derby.system.home"
as a String.  This seems to be a simple change and could easily be accommodated by first using
reflection to find the method that takes 0 parameters and if not found, retry with finding
the method that takes one string parameter?
> Brett
Hi Brett,

You could use 
to get the value of derby.system.home. That method will wrap the call to 
System.getProperty() in a privileged block which runs with the 
privileges granted to the Derby engine jar. PropertyUtil isn't part of 
the Derby public api so this isn't technically a supported approach and 
we reserve the right to change the behavior of that class. However, that 
class doesn't change much so you can probably get away with this.  At 
the end of this message there's an example dummy error logger which uses 
PropertyUtil to lookup the value of derby.system.home. To test this out, 
boot the network server with this setting:


Hope this helps,

import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;

import org.apache.derby.iapi.services.property.PropertyUtil;

public class DummyErrorLogger   extends OutputStreamWriter
     public  static  final   Writer  DEL = makeErrorLogger();

     public  DummyErrorLogger( OutputStream os )
         super( os );

     private  static  DummyErrorLogger    makeErrorLogger()
         System.out.println( "Making the error logger..." );

         String  derbySystemHome = PropertyUtil.getSystemProperty( 
"derby.system.home" );
         System.out.println( "derbySystemHome = " + derbySystemHome );

         return new DummyErrorLogger( System.out );


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