ChainBuilder


1   // Copyright 2005 The Apache Software Foundation
2   //
3   // Licensed under the Apache License, Version 2.0 (the "License");
4   // you may not use this file except in compliance with the License.
5   // You may obtain a copy of the License at
6   //
7   //     http://www.apache.org/licenses/LICENSE-2.0
8   //
9   // Unless required by applicable law or agreed to in writing, software
10  // distributed under the License is distributed on an "AS IS" BASIS,
11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12  // See the License for the specific language governing permissions and
13  // limitations under the License.
14  
15  package org.apache.hivemind.lib.chain;
16  
17  import java.util.List  ;
18  
19  /**
20   * Service interface for <code>hivemind.lib.ChainBuilder</code>, a service which can assemble an
21   * implementation based on a command interface, and an ordered list of objects implementing that
22   * interface (the "commands"). This is an implementation of the Gang of Four Chain Of Command
23   * pattern.
24   * <p>
25   * For each method in the interface, the chain implementation will call the corresponding method on
26   * each command object in turn. If any of the command objects return true, then the chain of command
27   * stops and the initial method invocation returns true. Otherwise, the chain of command continues
28   * to the next command (and will return false if none of the commands returns true).
29   * <p>
30   * For methods whose return type is not boolean, the chain stops with the first non-null (for object
31   * types), or non-zero (for numeric types). The chain returns the value that was returned by the
32   * command. The chain If the method return type is void, all command will be invoked.
33   * <p>
34   * Method invocations will also be terminated if an exception is thrown.
35   * 
36   * @author Howard M. Lewis Ship
37   * @since 1.1
38   */
39  public interface ChainBuilder
40  {
41      /**
42       * Builds an implementation.
43       * 
44       * @param commandInterface
45       *            the interface the implementation implements.
46       * @param commands
47       *            a non-null list of command objects implementing the interface.
48       * @param toString
49       *            The value to be returned from the implementation's <code>toString()</code>
50       *            method (unless <code>toString()</code> is expressly part of the service
51       *            interface, in which case it is treated as any other method.
52       */
53      public Object   buildImplementation(Class   commandInterface, List   commands, String   toString);
54  }
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