@ Nullable protected < T > T resolveExpression ( String context , String expression , Class < T > type ) { if ( environment . containsProperty ( expression ) ) { return environment . getProperty ( expression , type ) . orElseThrow ( ( ) -> new ConfigurationException ( "Could not resolve expression: [" + expression + "] in placeholder ${" + context + "}" ) ) ; } if ( NameUtils . isEnvironmentName ( expression ) ) { String envVar = System . getenv ( expression ) ; if ( StringUtils . isNotEmpty ( envVar ) ) { return conversionService . convert ( envVar , type ) . orElseThrow ( ( ) -> new ConfigurationException ( "Could not resolve expression: [" + expression + "] in placeholder ${" + context + "}" ) ) ; } } return null ; }
Resolves a single expression .