001 /* 002 * Copyright 1999-2001,2004 The Apache Software Foundation. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017 package org.apache.commons.workflow; 018 019 020 /** 021 * <p>A <strong>Block</strong> is a Step that can include nested Steps. 022 * It is used to create Step implementations supporting conditional 023 * execution and iteration.</p> 024 * 025 * <p><strong>DESIGN NOTES</strong> - The <code>execute()</code> method will 026 * be called when the Block is first encountered in the normal flow of 027 * execution (as with any other Step), and each time the execution of the 028 * nested Steps associated with this Block. The Block implementation is 029 * responsible for satisfying the following contract requirements:</p> 030 * <ul> 031 * <li>Determine whether this is a first-time entry, or a repeated entry 032 * after execution of the nested Steps for this Block: 033 * <ul> 034 * <li>Peek at the top item on the <code>BlockState</code> stack maintained 035 * for us by the current <code>Context</code>.</li> 036 * <li>If the top item exists, and has a <code>block</code> property 037 * equal to the current Block, this is a repeated entry after execution 038 * of the nested Steps for this Block.</li> 039 * <li>If there is no top element, or the top element is for a different 040 * <code>Block</code>, this is the initial entry from the preceeding 041 * Step in the current Activity (or Block).</li> 042 * </ul> 043 * <li>When this is the initial entry into the Block, make a decision about 044 * whether the nested Steps should be executed: 045 * <ul> 046 * <li>If the nested Steps <strong>SHOULD</strong> be executed, create a 047 * new <code>BlockState</code> object (associated with this 048 * <code>Block</code>) and push it onto the <code>BlockState</code> 049 * stack. Then, set the next Step to be the first nested Step 050 * for this Block.</li> 051 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed, 052 * simply return. The next Step will have already been set to the 053 * next Step of the current Activity (or Block) at the same nesting 054 * level.</li> 055 * </ul></li> 056 * <li>When this is a repeated entry into the Block, make a decision about 057 * whether the nested Steps should be executed again: 058 * <ul> 059 * <li>If the nested Steps <strong>SHOULD</strong> be executed again, 060 * set the next Step to be the first nested Step for this Block.</li> 061 * <li>If the nested Steps <strong>SHOULD NOT</strong> be executed again, 062 * pop our <code>BlockState</code> object off of the stack 063 * maintained by our <code>Context</code>. Then, set the next Step 064 * to the <code>nextStep</code> property of this Block, which will 065 * cause execution to flow past the Block.</li> 066 * </ul> 067 * </ul> 068 * 069 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $ 070 * @author Craig R. McClanahan 071 */ 072 073 public interface Block extends Owner, Step { 074 075 076 // --------------------------------------------------------- Public Methods 077 078 079 }