jakarta.decorator

Annotation Type Delegate

@Target(value={FIELD,PARAMETER})
 @Retention(value=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 );
    }
    ...
 }
 

Author:

Gavin King, Pete Muir

See Also:

@Decorator specifies that a class is a decorator.