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 /*
  * JBoss, Home of Professional Open Source
  * Copyright 2010, Red Hat, Inc., and individual contributors
  * by the @authors tag. See the copyright.txt in the distribution for a
  * full listing of individual contributors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,  
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.decorator;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

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 java.lang.IllegalStateException.

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

Author(s):
Gavin King
Pete Muir
See also:
javax.decorator.Decorator &.064;Decorator specifies that a class is a decorator.
public @interface Delegate {
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