1 /**
2 *
3 * Licensed to the Apache Software Foundation (ASF) under one or more
4 * contributor license agreements. See the NOTICE file distributed with
5 * this work for additional information regarding copyright ownership.
6 * The ASF licenses this file to You under the Apache License, Version 2.0
7 * (the "License"); you may not use this file except in compliance with
8 * the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.apache.xbean.recipe;
19
20 /**
21 * Reference is a named (lazy) reference from one object to another. This data class is updated when the reference
22 * is resolved which can be immedately when the ref is created, or later when an instance with the referenced
23 * name is created.
24 * <p/>
25 * When the reference is resolved, an optional Action will be invoked which is commonly used to update a
26 * property on the source object of the reference.
27 */
28 public class Reference {
29 private final String name;
30 private boolean resolved;
31 private Object instance;
32 private Action action;
33
34 /**
35 * Create a reference to the specified name.
36 * @param name the name of the referenced object
37 */
38 public Reference(String name) {
39 this.name = name;
40 }
41
42 /**
43 * Gets the name of the referenced object.
44 * @return name the name of the referenced object
45 */
46 public String getName() {
47 return name;
48 }
49
50 /**
51 * Has this reference been resolved?
52 * @return true if the reference has been resolved; false otherwise
53 */
54 public boolean isResolved() {
55 return resolved;
56 }
57
58 /**
59 * Gets the referenced object instance or null if the reference has not been resolved yet;
60 *
61 * @return the referenced object instance or null
62 */
63 public Object get() {
64 return instance;
65 }
66
67 /**
68 * Sets the referenced object instance. If an action is registered the onSet method is invoked.
69 *
70 * @param object the reference instance
71 */
72 public void set(Object object) {
73 if (resolved) {
74 throw new ConstructionException("Reference has already been resolved");
75 }
76 resolved = true;
77 this.instance = object;
78 if (action != null) {
79 action.onSet(this);
80 }
81 }
82
83 /**
84 * Registers an action to invoke when the instance is set. If the instance, has already been set, the
85 * onSet method will immedately be invoked.
86 *
87 * @return the action to invoke when this refernce is resolved; not null
88 */
89 public void setAction(Action action) {
90 if (action == null) {
91 throw new NullPointerException("action is null");
92 }
93 this.action = action;
94 if (resolved) {
95 action.onSet(this);
96 }
97 }
98
99 public static interface Action {
100 void onSet(Reference ref);
101 }
102 }