Module jakarta.cdi

Annotation Type Delegate


  • @Target({FIELD,PARAMETER})
    @Retention(RUNTIME)
    @Documented
    public @interface Delegate

    Identifies the delegate injection point of a decorator. May be applied to a field, bean constructor parameter or initializer method parameter of a decorator bean class.

     @Decorator 
     class TimestampLogger implements Logger { 
        @Inject @Delegate @Any Logger logger; 
        ... 
     }
     
     @Decorator 
     class TimestampLogger implements Logger { 
        private Logger logger;
        
        @Inject
        public TimestampLogger(@Delegate @Debug Logger logger) { 
           this.logger=logger; 
        } 
        ... 
     }
     

    A decorator must have exactly one delegate injection point. The delegate injection point must be an injected field, initializer method parameter or bean constructor method parameter.

    The container injects a delegate object to the delegate injection point. The delegate object implements the delegate type and delegates method invocations along the decorator stack. When the container calls a decorator during business method interception, the decorator may invoke any method of the delegate object. If a decorator invokes the delegate object at any other time, the invoked method throws an IllegalStateException.

     @Decorator 
     class TimestampLogger implements Logger { 
        @Inject @Delegate @Any Logger logger; 
        
        void log(String message) {
           logger.log( timestamp() + ": " + message );
        }
        ...
     }
     

    CDI Lite implementations are not required to provide support for decorators.

    Author:
    Gavin King, Pete Muir
    See Also:
    Decorator specifies that a class is a decorator.