1 /*
2 * Copyright 1999-2001,2004 The Apache Software Foundation.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package org.apache.commons.workflow.io;
18
19
20 import java.util.EmptyStackException;
21 import org.apache.commons.workflow.Context;
22 import org.apache.commons.workflow.StepException;
23 import org.apache.commons.workflow.base.BaseStep;
24
25
26 /**
27 * <p>Write the top value from the evaluation stack to standard output,
28 * without removing it.</p>
29 *
30 * <p><strong>WARNING</strong> - This will probably be
31 * replaced later by a more general purpose input/output mechanism.</p>
32 *
33 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $
34 * @author Craig R. McClanahan
35 */
36
37 public class PeekStep extends BaseStep {
38
39
40 // ----------------------------------------------------------= Constructors
41
42
43 /**
44 * Construct a default instance of this Step.
45 */
46 public PeekStep() {
47
48 super();
49
50 }
51
52
53 /**
54 * Construct an instance of this Step with the specified identifier.
55 *
56 * @param id Step identifier
57 */
58 public PeekStep(String id) {
59
60 super();
61 setId(id);
62
63 }
64
65
66 // --------------------------------------------------------- Public Methods
67
68
69 /**
70 * Perform the executable actions related to this Step, in the context of
71 * the specified Context.
72 *
73 * @param context The Context that is tracking our execution state
74 *
75 * @exception StepException if a processing error has occurred
76 */
77 public void execute(Context context) throws StepException {
78
79 // Retrieve a copy of the top value from the evaluation stack
80 Object value = null;
81 try {
82 value = context.peek();
83 } catch (EmptyStackException e) {
84 throw new StepException("Evaluation stack is empty", e, this);
85 }
86
87 // Display it to standard output
88 System.out.println(value);
89
90 }
91
92
93 }