001// Licensed under the Apache License, Version 2.0 (the "License");
002// you may not use this file except in compliance with the License.
003// You may obtain a copy of the License at
004//
005//     http://www.apache.org/licenses/LICENSE-2.0
006//
007// Unless required by applicable law or agreed to in writing, software
008// distributed under the License is distributed on an "AS IS" BASIS,
009// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
010// See the License for the specific language governing permissions and
011// limitations under the License.
012
013package org.apache.tapestry5.ioc.services;
014
015import java.util.List;
016
017/**
018 * A service which can assemble an implementation based on a command interface, and an ordered list of objects
019 * implementing that interface (the "commands"). This is an implementation of the Gang of Four Chain Of Command
020 * pattern.
021 *
022 * For each method in the interface, the chain implementation will call the corresponding method on each command object
023 * in turn (with the order defined by the list). If any of the command objects return true, then the chain of command
024 * stops and the initial method invocation returns true. Otherwise, the chain of command continues to the next command
025 * (and will return false if none of the commands returns true).
026 *
027 * For methods whose return type is not boolean, the chain stops with the first non-null (for object types), or non-zero
028 * (for numeric types). The chain returns the value that was returned by the command. If the method return type is void,
029 * all commands will be invoked.
030 *
031 * Method invocations will also be terminated if an exception is thrown.
032 */
033public interface ChainBuilder
034{
035    /**
036     * Creates a chain instance from a command interface and a list of commands (implementing the interface).
037     * @param <T> the command interface type
038     * @param commandInterface the command interface
039     * @param commands the list of commands to be chained
040     * @return the chain instance
041     */
042    <T> T build(Class<T> commandInterface, List<T> commands);
043}