Access Properties Defined in Logback programmatically

Question

I have an administration console I'm building, and I want to display the logs created in Logback for my application. However, where those logs are stored is different per environment. I have several property files that define where the logs are stored:

<configuration>
  <property resource='log.properties'/>
  <property resource='log.${ENV:-prod}.properties'/>

  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${log.dir}/sync.log</file>
  ...
</configuration>

I'd like to find the value of ${log.dir} from Logback's Java API. I'd tried the following, but it doesn't have any of the properties defined in the resources. For example:

 LoggerContext loggerContext = (LoggerContext) LoggerFactory.getILoggerFactory();
 String logDir = loggerContext.getProperty("log.dir"); // this always returns null

So my question is what API should I be using?

Answer 1

By default, properties are defined in "local" scope. However, you can force a property to have context scope, in which case it's pretty easy to get the value of the property:

 LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
 String val = lc.getProperty(aString);

Defining properties in "context" scope is considered a little heavy handed. Instead of defining all/many properties in context scope, you could define only a single property in context scope. Here is an example:

<configuration>
  <!-- get many props from a file -->
  <property resource='log.properties'/>
  <-- set only one to be in context scope -->
  <property scope="context" name="log.dir.ctx" value="${log.dir}" />
  ...
</configuration>

You could then obtain the value you are looking for with:

 LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
 String val = lc.getProperty("log.dir.ctx");