String resolve(String variableName) {
        if (variableName == null) {
            throw new IllegalArgumentException("Method argument variableName must not be null");
        }

        for (PlaceholderVariableResolver resolver : resolvers) {
            String resolved = resolver.resolve(variableName);
            if (resolved != null) {
                return resolved;
            }
        }

        String resolved = getenv(variableName);
        if (resolved != null) {
            return resolved;
        }

        return getProperty(variableName, null);
    }
String resolve ( String variableName ) { if ( variableName == null ) { throw new IllegalArgumentException ( "Method argument variableName must not be null" ) ; } for ( PlaceholderVariableResolver resolver : resolvers ) { String resolved = resolver . resolve ( variableName ) ; if ( resolved != null ) { return resolved ; } } String resolved = getenv ( variableName ) ; if ( resolved != null ) { return resolved ; } return getProperty ( variableName , null ) ; }
@param variableName must not be <code>null</code>.
@return the resolved value, or <code>null</code> if no value could be resolved.