1 /**
2 * Copyright 2005-2014 The Kuali Foundation
3 *
4 * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
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 package org.kuali.rice.krad.uif.lifecycle.initialize;
17
18 import org.apache.commons.lang.StringUtils;
19 import org.kuali.rice.krad.uif.UifConstants;
20 import org.kuali.rice.krad.uif.lifecycle.LifecycleElementState;
21 import org.kuali.rice.krad.uif.lifecycle.ViewLifecycle;
22 import org.kuali.rice.krad.uif.lifecycle.ViewLifecycleTaskBase;
23 import org.kuali.rice.krad.uif.util.LifecycleElement;
24 import org.kuali.rice.krad.uif.view.View;
25 import org.kuali.rice.krad.uif.view.ViewIndex;
26
27 /**
28 * Assign a unique ID to the component, if one has not already been assigned.
29 *
30 * @author Kuali Rice Team (rice.collab@kuali.org)
31 */
32 public class AssignIdsTask extends ViewLifecycleTaskBase<LifecycleElement> {
33
34 /**
35 * Create a task to assign component IDs during the initialize phase.
36 *
37 * @param elementState The initialize phase for the component.
38 */
39 public AssignIdsTask(LifecycleElementState elementState) {
40 super(elementState, LifecycleElement.class);
41 }
42
43 /**
44 * Generate a new ID for a lifecycle element at the current phase.
45 *
46 * <p>
47 * This method used a product of primes similar to the one used for generating String hash
48 * codes. In order to minimize to collisions a large prime is used, then when collisions are
49 * detected a different large prime is used to generate an alternate ID.
50 * </p>
51 *
52 * <p>
53 * The hash code that the generated ID is based on is equivalent (though not identical) to
54 * taking the hash code of the string concenation of all class names, non-null IDs, and
55 * successor index positions in the lifecycle phase tree for all predecessors of the current
56 * phase. This technique leads to a reliably unique ID that is also repeatable across server
57 * instances and test runs.
58 * </p>
59 *
60 * <p>
61 * The use of large primes by this method minimizes collisions, and therefore reduces the
62 * likelihood of a race condition causing components to come out with different IDs on different
63 * server instances and/or test runs.
64 * </p>
65 *
66 * @param element The lifecycle element for which to generate an ID.
67 * @param view View containing the lifecycle element.
68 * @return An ID, unique within the current view, for the given element.
69 *
70 * @see ViewIndex#observeAssignedId(String)
71 * @see String#hashCode() for the algorithm this method is based on.
72 */
73 public static String generateId(LifecycleElement element, View view) {
74 // Calculate a hash code based on the path to the top of the phase tree
75 // without building a string.
76 int prime = 6971;
77
78 // Initialize hash to the class of the lifecycle element
79 int hash = element.getClass().getName().hashCode();
80
81 // Add the element's path to the hash code.
82 hash += prime;
83 if (element.getViewPath() != null) {
84 hash += element.getViewPath().hashCode();
85 }
86
87 // Eliminate negatives without losing precision, and express in base-36
88 String id = Long.toString(((long) hash) - ((long) Integer.MIN_VALUE), 36);
89 while (!view.getViewIndex().observeAssignedId(id)) {
90 // Iteratively take the product of the hash and another large prime
91 // until a unique ID has been generated.
92 hash *= 4507;
93 id = Long.toString(((long) hash) - ((long) Integer.MIN_VALUE), 36);
94 }
95
96 return UifConstants.COMPONENT_ID_PREFIX + id;
97 }
98
99 /**
100 * {@inheritDoc}
101 */
102 @Override
103 protected void performLifecycleTask() {
104 LifecycleElement element = getElementState().getElement();
105
106 if (StringUtils.isBlank(element.getId())) {
107 element.setId(generateId(element, ViewLifecycle.getView()));
108 }
109 }
110
111 }