1 /*
2 * Copyright 2012-2013 smartics, Kronseder & Reiner GmbH
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 package de.smartics.properties.api.core.domain;
17
18 import java.io.ObjectStreamException;
19 import java.io.Serializable;
20
21 import org.apache.commons.lang.StringUtils;
22
23 /**
24 * Provides information about the expression to evaluate a default value for a
25 * property.
26 */
27 public final class PropertyExpression implements Serializable
28 {
29 // ********************************* Fields *********************************
30
31 // --- constants ------------------------------------------------------------
32
33 /**
34 * The class version identifier.
35 */
36 private static final long serialVersionUID = 1L;
37
38 /**
39 * The expression instance to signal that there is no property expression.
40 */
41 public static final PropertyExpression NO_EXPRESSION =
42 new PropertyExpression(null);
43
44 // --- members --------------------------------------------------------------
45
46 /**
47 * The expression string. May be <code>null</code>.
48 *
49 * @serial
50 */
51 private final String expression;
52
53 // ****************************** Initializer *******************************
54
55 // ****************************** Constructors ******************************
56
57 /**
58 * Default constructor.
59 *
60 * @param expression the expression string.
61 */
62 private PropertyExpression(final String expression)
63 {
64 this.expression = expression;
65 }
66
67 // ****************************** Inner Classes *****************************
68
69 // ********************************* Methods ********************************
70
71 // --- init -----------------------------------------------------------------
72
73 // --- create ---------------------------------------------------------------
74
75 /**
76 * Creates an instance of {@link PropertyExpression} with the given expression
77 * string.
78 *
79 * @param expression the expression string.
80 * @return the created instance. If the {@code expression} is blank, the
81 * singleton expression {@link #NO_EXPRESSION} is returned.
82 */
83 public static PropertyExpression create(final String expression)
84 {
85 if (StringUtils.isBlank(expression))
86 {
87 return NO_EXPRESSION;
88 }
89
90 return new PropertyExpression(expression);
91 }
92
93 // --- get&set --------------------------------------------------------------
94
95 /**
96 * Checks if an expression string is present.
97 *
98 * @return <code>true</code> if the expression string is not <code>null</code>
99 * , <code>false</code> if it is <code>null</code>.
100 */
101 public boolean hasExpression()
102 {
103 return expression != null;
104 }
105
106 /**
107 * Returns the expression string.
108 *
109 * @return the expression string. May be <code>null</code>.
110 */
111 public String getExpression()
112 {
113 return expression;
114 }
115
116 // --- business -------------------------------------------------------------
117
118 // --- object basics --------------------------------------------------------
119
120 /**
121 * Special treatment for serializable singletons.
122 *
123 * @return returns a reference to the (truly) unique singleton.
124 */
125 private Object readResolve() throws ObjectStreamException
126 {
127 if (StringUtils.isBlank(expression))
128 {
129 return NO_EXPRESSION;
130 }
131
132 return this;
133 }
134
135 /**
136 * Returns the name of the type.
137 *
138 * @return the name of the type.
139 */
140 @Override
141 public String toString()
142 {
143 return expression != null ? expression : StringUtils.EMPTY;
144 }
145 }