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.core;
18
19
20 import java.util.EmptyStackException;
21 import org.apache.commons.workflow.Activity;
22 import org.apache.commons.workflow.Context;
23 import org.apache.commons.workflow.StepException;
24 import org.apache.commons.workflow.base.BaseStep;
25
26
27 /**
28 * <p>Pop the top value from the evaluation stack, which must be an
29 * <code>Activity</code>, and initiate a "subroutine call" to execute
30 * this Activity before resuming the current one.</p>
31 *
32 * <p><strong>NOTE</strong> - The means by which the Activity on the top
33 * of the stack was acquired is NOT mandated by this Step implementation.</p>
34 *
35 * @version $Revision: 155475 $ $Date: 2005-02-26 13:31:11 +0000 (Sat, 26 Feb 2005) $
36 * @author Craig R. McClanahan
37 */
38
39 public class CallStep extends BaseStep {
40
41
42 // ----------------------------------------------------------= Constructors
43
44
45 /**
46 * Construct a default instance of this Step.
47 */
48 public CallStep() {
49
50 super();
51
52 }
53
54
55 /**
56 * Construct an instance of this Step with the specified identifier.
57 *
58 * @param id Step identifier
59 */
60 public CallStep(String id) {
61
62 super();
63 setId(id);
64
65 }
66
67
68 // --------------------------------------------------------- Public Methods
69
70
71 /**
72 * Perform the executable actions related to this Step, in the context of
73 * the specified Context.
74 *
75 * @param context The Context that is tracking our execution state
76 *
77 * @exception StepException if a processing error has occurred
78 */
79 public void execute(Context context) throws StepException {
80
81 // Pop the evaluation stack
82 Object value = null;
83 try {
84 value = context.pop();
85 } catch (EmptyStackException e) {
86 throw new StepException("Evaluation stack is empty", e, this);
87 }
88
89 // Call the requested Activity
90 if (!(value instanceof Activity))
91 throw new StepException("Top of stack is not an Activity", this);
92 context.call((Activity) value);
93
94 }
95
96
97 }