Return the ordinal for this config source. If a property is specified in multiple config sources, the value
in the config source with the highest ordinal takes precedence.
For the config sources with the same ordinal value, the config source names will
be used for sorting according to string sorting criteria.
Note that this property only gets evaluated during ConfigSource discovery.
The default ordinals for the default config sources:
System properties (ordinal=400)
Environment properties (ordinal=300)
Some operating systems allow only alphabetic characters or an underscore(_), in environment variables.
Other characters such as ., /, etc may be disallowed.
In order to set a value for a config property that has a name containing such disallowed characters from an environment variable,
the following rules are used.
This ConfigSource searches for potentially 3 environment variables with a given property name (e.g. "com.ACME.size"):
Exact match (i.e. "com.ACME.size")
Replace the character that is neither alphanumeric nor '_' with '_' (i.e. "com_ACME_size")
Replace the character that is neither alphanumeric nor '_' with '_' and convert to upper case
The first environment variable that is found is returned by this ConfigSource.
Any ConfigSource part of an application will typically use an ordinal between 0 and 200.
ConfigSource provided by the container or 'environment' typically use an ordinal higher than 200.
A framework which intends have values overwritten by the application will use ordinals between 0 and 100.
The property "config_ordinal" can be specified to override the default value.