Custom Classloaders

[Robert Scholte]

Hi,

 

I'm working on a new application, using jlink to build it.

One challenge is related to the simplelogger of SLF4J (as SLF4J-api is
probably the most used logging api, the simplelogger implementation matches
my requirements)

There are 2 things that I would like to adjust:

1.	Simplelogger uses the classloader to find the
simplelogger.properties (
https://github.com/qos-ch/slf4j/blob/master/slf4j-simple/src/main/java/org/s
lf4j/simple/SimpleLoggerConfiguration.java#L107-L130 ). 

However, I want to externalize this file to
${java.home}/conf/simplelogger.properties, so users can adjust it to their
preferences. If I could change the classloader I could control where to find
this file.

When bundling simplelogger with jlink the jar will end up in the
AppClassloader due to the SimpleServiceProvider. 

The only option to avoid this, is to move this jar to a separate directory
and when making a new ModuleLayer, and use ModuleFinder with this path. 

But still, I see no way to change the classloader for this jar.

 

2.	The simplelogger.properties is the default configuration, and I want
to make it possible to override these values. 

The simplelogger offers the option to use SystemProperties to override
values from simplelogger.properties.

I want to avoid that the System.properties will be polluted with entities
just for logging.

As far as I know it is not possible to scope System.properties: they are
global, available for every part of the application.

Another idea I had was to extend the simplelogging.properties resources at
runtime using the SequenceInputStream, and for this I also need to have
control over the classloader, as it requires to override the
ClassLoader.getResourceAsStream()

 

It seems both challenges could be solved if could control the classloader
(while still being protected by jdk.internal.loader.Loader).

 

Am I missing some feature or it there another way to solve these issues?

 

Best,

Robert 

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