1 package org.apache.maven.plugin.coreit;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.lang.reflect.Array;
23 import java.lang.reflect.Field;
24 import java.lang.reflect.Method;
25 import java.util.Arrays;
26 import java.util.Collection;
27 import java.util.List;
28 import java.util.Map;
29
30 /**
31 * Assists in evaluating expressions.
32 *
33 * @author Benjamin Bentmann
34 *
35 */
36 class ExpressionUtil
37 {
38
39 private static final Object[] NO_ARGS = {};
40
41 private static final Class[] NO_PARAMS = {};
42
43 private static final Class[] OBJECT_PARAM = { Object.class };
44
45 private static final Class[] STRING_PARAM = { String.class };
46
47 /**
48 * Evaluates the specified expression. Expressions are composed of segments which are separated by a forward slash
49 * ('/'). Each segment specifies a (public) bean property of the current object and drives the evaluation further
50 * down the object graph. For lists, arrays and maps segments can additionally specify the index/key of an element.
51 * The initial segment denotes the root object and the parameter <code>contexts</code> is used to specify which
52 * root objects are available. For instance, if <code>contexts</code> maps the token "project" to a Maven project
53 * instance, the expression "project/build/resources/0/directory" specifies the first resource directory of the
54 * project.
55 *
56 * @param expression The expression to evaluate, may be <code>null</code>.
57 * @param contexts The possible root objects for the expression evaluation, indexed by their identifying token,
58 * must
59 * not be <code>null</code>.
60 * @return The value of the expression or <code>null</code> if the expression could not be evaluated.
61 */
62 public static Object evaluate( String expression, Map contexts )
63 {
64 Object value = null;
65
66 if ( expression != null && expression.length() > 0 )
67 {
68 List segments = Arrays.asList( expression.split( "/", 0 ) );
69 if ( !segments.isEmpty() )
70 {
71 Object context = contexts.get( segments.get( 0 ) );
72 if ( context != null )
73 {
74 value = evaluate( context, segments.subList( 1, segments.size() ) );
75 }
76 }
77 }
78
79 return value;
80 }
81
82 /**
83 * Evaluates the given expression segments against the specified object.
84 *
85 * @param context The object to evaluate the segments against, may be <code>null</code>.
86 * @param segments The expression segments to evaluate, must not be <code>null</code>.
87 * @return The value of the evaluation or <code>null</code> if the segments could not be evaluated.
88 */
89 private static Object evaluate( Object context, List segments )
90 {
91 Object value = null;
92
93 if ( segments.isEmpty() )
94 {
95 value = context;
96 }
97 else if ( context != null )
98 {
99 Object target = null;
100 String segment = (String) segments.get( 0 );
101 if ( segment.length() <= 0 )
102 {
103 value = context;
104 }
105 else if ( context.getClass().isArray() && Character.isDigit( segment.charAt( 0 ) ) )
106 {
107 try
108 {
109 int index = Integer.parseInt( segment );
110 target = Array.get( context, index );
111 }
112 catch ( RuntimeException e )
113 {
114 // invalid index, just ignore
115 }
116 }
117 else if ( ( context instanceof List ) && Character.isDigit( segment.charAt( 0 ) ) )
118 {
119 try
120 {
121 int index = Integer.parseInt( segment );
122 target = ( (List) context ).get( index );
123 }
124 catch ( RuntimeException e )
125 {
126 // invalid index, just ignore
127 }
128 }
129 else
130 {
131 target = getProperty( context, segment );
132 }
133 value = evaluate( target, segments.subList( 1, segments.size() ) );
134 }
135
136 return value;
137 }
138
139 /**
140 * Gets the value of a (public) bean property from the specified object.
141 *
142 * @param context The object whose bean property should be retrieved, must not be <code>null</code>.
143 * @param property The name of the bean property, must not be <code>null</code>.
144 * @return The value of the bean property or <code>null</code> if the property does not exist.
145 */
146 static Object getProperty( Object context, String property )
147 {
148 Object value;
149
150 Class type = context.getClass();
151 if ( context instanceof Collection )
152 {
153 type = Collection.class;
154 }
155 else if ( context instanceof Map )
156 {
157 type = Map.class;
158 }
159
160 try
161 {
162 try
163 {
164 Method method = type.getMethod( property, NO_PARAMS );
165 value = method.invoke( context, NO_ARGS );
166 }
167 catch ( NoSuchMethodException e )
168 {
169 try
170 {
171 String name = "get" + Character.toUpperCase( property.charAt( 0 ) ) + property.substring( 1 );
172 Method method = type.getMethod( name, NO_PARAMS );
173 value = method.invoke( context, NO_ARGS );
174 }
175 catch ( NoSuchMethodException e1 )
176 {
177 try
178 {
179 String name = "is" + Character.toUpperCase( property.charAt( 0 ) ) + property.substring( 1 );
180 Method method = type.getMethod( name, NO_PARAMS );
181 value = method.invoke( context, NO_ARGS );
182 }
183 catch ( NoSuchMethodException e2 )
184 {
185 try
186 {
187 Method method;
188 try
189 {
190 method = type.getMethod( "get", STRING_PARAM );
191 }
192 catch ( NoSuchMethodException e3 )
193 {
194 method = type.getMethod( "get", OBJECT_PARAM );
195 }
196 value = method.invoke( context, new Object[]{ property } );
197 }
198 catch ( NoSuchMethodException e3 )
199 {
200 try
201 {
202 Field field = type.getField( property );
203 value = field.get( context );
204 }
205 catch ( NoSuchFieldException e4 )
206 {
207 if ( "length".equals( property ) && type.isArray() )
208 {
209 value = Array.getLength( context );
210 }
211 else
212 {
213 throw e4;
214 }
215 }
216 }
217 }
218 }
219 }
220 }
221 catch ( Exception e )
222 {
223 value = null;
224 }
225 return value;
226 }
227
228 }