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.io; 018 019 020 import java.util.EmptyStackException; 021 import org.apache.commons.workflow.Context; 022 import org.apache.commons.workflow.StepException; 023 import org.apache.commons.workflow.base.BaseStep; 024 025 026 /** 027 * <p>Write the top value from the evaluation stack to standard output, 028 * without removing it.</p> 029 * 030 * <p><strong>WARNING</strong> - This will probably be 031 * replaced later by a more general purpose input/output mechanism.</p> 032 * 033 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $ 034 * @author Craig R. McClanahan 035 */ 036 037 public class PeekStep extends BaseStep { 038 039 040 // ----------------------------------------------------------= Constructors 041 042 043 /** 044 * Construct a default instance of this Step. 045 */ 046 public PeekStep() { 047 048 super(); 049 050 } 051 052 053 /** 054 * Construct an instance of this Step with the specified identifier. 055 * 056 * @param id Step identifier 057 */ 058 public PeekStep(String id) { 059 060 super(); 061 setId(id); 062 063 } 064 065 066 // --------------------------------------------------------- Public Methods 067 068 069 /** 070 * Perform the executable actions related to this Step, in the context of 071 * the specified Context. 072 * 073 * @param context The Context that is tracking our execution state 074 * 075 * @exception StepException if a processing error has occurred 076 */ 077 public void execute(Context context) throws StepException { 078 079 // Retrieve a copy of the top value from the evaluation stack 080 Object value = null; 081 try { 082 value = context.peek(); 083 } catch (EmptyStackException e) { 084 throw new StepException("Evaluation stack is empty", e, this); 085 } 086 087 // Display it to standard output 088 System.out.println(value); 089 090 } 091 092 093 }