001    // Copyright 2006 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.services;
016    
017    import java.util.List;
018    
019    /**
020     * A service which can assemble an implementation based on a command interface, and an ordered list of objects
021     * implementing that interface (the "commands"). This is an implementation of the Gang of Four Chain Of Command
022     * pattern.
023     * <p/>
024     * For each method in the interface, the chain implementation will call the corresponding method on each command object
025     * in turn (with the order defined by the list). If any of the command objects return true, then the chain of command
026     * stops and the initial method invocation returns true. Otherwise, the chain of command continues to the next command
027     * (and will return false if none of the commands returns true).
028     * <p/>
029     * For methods whose return type is not boolean, the chain stops with the first non-null (for object types), or non-zero
030     * (for numeric types). The chain returns the value that was returned by the command. If the method return type is void,
031     * all commands will be invoked.
032     * <p/>
033     * Method invocations will also be terminated if an exception is thrown.
034     */
035    public interface ChainBuilder
036    {
037        /**
038         * Creates a chain instance from a command interface and a list of commands (implementing the interface).
039         */
040        <T> T build(Class<T> commandInterface, List<T> commands);
041    }