org.apache.isis.commons.handler.ChainOfResponsibility Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* to you 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
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* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
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*/
package org.apache.isis.commons.handler;
import java.util.List;
import java.util.Optional;
/**
* Building blocks for the Chain of Responsibility design pattern.
*
* Chain of Responsibility allows passing requests along the chain of handlers,
* until one of them handles the request.
*
* @since 2.0
*
* @param request type
* @param response type
*/
public interface ChainOfResponsibility {
/**
* The {@code request} is passed along the chain of handlers, until one of them handles the request.
* @param request
* @return response of the first handler that handled the request wrapped in an Optional,
* or an empty Optional, if no handler handled the request
*/
Optional handle(X request);
/**
* A chain of responsibility is made up of handlers, that are asked in sequence,
* whether they handle a request.
*
* @since 2.0
*
* @param request type
* @param response type
*/
static interface Handler {
boolean isHandling(X request);
R handle(X request);
}
/**
* Creates a new ChainOfResponsibility of given {@code chainOfHandlers}
* @param
* @param
* @param chainOfHandlers
*/
static ChainOfResponsibility
of(
final List> chainOfHandlers) {
return request -> {
final Optional responseIfAny = chainOfHandlers.stream()
.filter(h -> h.isHandling(request))
.findFirst()
.map(h -> h.handle(request));
return responseIfAny;
};
}
}