The quickfix.SessionSettings class supports variable interpolation using a configured set of substitution values. By default, the substitution values are JVM system properties.

The variable syntax is "${variable}". For example, if system property "user.name" is "USER"...

FileStorePath=logs/${user.name}

becomes...

FileStorePath=logs/USER

Remember that system properties can be specified to the JVM using the -D argument on the command line. You can also use the method SessionSettings.setVariableValues() to configure your own set of substitution values.

Properties settingsVariableValues= new Properties();
settingsVariableValues.put("myvariable", "somevalue");
... other custom settings

settings.setVariableValues(settingsVariableValues);

The substitution values could be loaded from a property file.

Properties myCustomSettingsVariables = new Properties();
myCustomSettingsVariables.load(inputStream);
settings.setVariableValueS(myCustomSettingsVariables);

You can implement simple property inheritance by constructing a chain of java.util.Properties objects.

Properties settingsVariableValues= new Properties(System.getProperties());
settingsVariableValues.put("myvariable", "somevalue");
... other custom settings, possibly overriding the default system properties

These techniques give you a simple way to create templates of settings files that are customized based on run time values.