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 * @version $Id: ExpressionUtil.java 705750 2008-10-17 21:07:54Z bentmann $
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, must
58 * not be <code>null</code>.
59 * @return The value of the expression or <code>null</code> if the expression could not be evaluated.
60 */
61 public static Object evaluate( String expression, Map contexts )
62 {
63 Object value = null;
64
65 if ( expression != null && expression.length() > 0 )
66 {
67 List segments = Arrays.asList( expression.split( "/", 0 ) );
68 if ( !segments.isEmpty() )
69 {
70 Object context = contexts.get( segments.get( 0 ) );
71 if ( context != null )
72 {
73 value = evaluate( context, segments.subList( 1, segments.size() ) );
74 }
75 }
76 }
77
78 return value;
79 }
80
81 /**
82 * Evaluates the given expression segments against the specified object.
83 *
84 * @param context The object to evaluate the segments against, may be <code>null</code>.
85 * @param segments The expression segments to evaluate, must not be <code>null</code>.
86 * @return The value of the evaluation or <code>null</code> if the segments could not be evaluated.
87 */
88 private static Object evaluate( Object context, List segments )
89 {
90 Object value = null;
91
92 if ( segments.isEmpty() )
93 {
94 value = context;
95 }
96 else if ( context != null )
97 {
98 Object target = null;
99 String segment = (String) segments.get( 0 );
100 if ( segment.length() <= 0 )
101 {
102 value = context;
103 }
104 else if ( context.getClass().isArray() && Character.isDigit( segment.charAt( 0 ) ) )
105 {
106 try
107 {
108 int index = Integer.parseInt( segment );
109 target = Array.get( context, index );
110 }
111 catch ( RuntimeException e )
112 {
113 // invalid index, just ignore
114 }
115 }
116 else if ( ( context instanceof List ) && Character.isDigit( segment.charAt( 0 ) ) )
117 {
118 try
119 {
120 int index = Integer.parseInt( segment );
121 target = ( (List) context ).get( index );
122 }
123 catch ( RuntimeException e )
124 {
125 // invalid index, just ignore
126 }
127 }
128 else
129 {
130 target = getProperty( context, segment );
131 }
132 value = evaluate( target, segments.subList( 1, segments.size() ) );
133 }
134
135 return value;
136 }
137
138 /**
139 * Gets the value of a (public) bean property from the specified object.
140 *
141 * @param context The object whose bean property should be retrieved, must not be <code>null</code>.
142 * @param property The name of the bean property, must not be <code>null</code>.
143 * @return The value of the bean property or <code>null</code> if the property does not exist.
144 */
145 static Object getProperty( Object context, String property )
146 {
147 Object value;
148
149 Class type = context.getClass();
150 if ( context instanceof Collection )
151 {
152 type = Collection.class;
153 }
154 else if ( context instanceof Map )
155 {
156 type = Map.class;
157 }
158
159 try
160 {
161 try
162 {
163 Method method = type.getMethod( property, NO_PARAMS );
164 value = method.invoke( context, NO_ARGS );
165 }
166 catch ( NoSuchMethodException e )
167 {
168 try
169 {
170 String name = "get" + Character.toUpperCase( property.charAt( 0 ) ) + property.substring( 1 );
171 Method method = type.getMethod( name, NO_PARAMS );
172 value = method.invoke( context, NO_ARGS );
173 }
174 catch ( NoSuchMethodException e1 )
175 {
176 try
177 {
178 String name = "is" + Character.toUpperCase( property.charAt( 0 ) ) + property.substring( 1 );
179 Method method = type.getMethod( name, NO_PARAMS );
180 value = method.invoke( context, NO_ARGS );
181 }
182 catch ( NoSuchMethodException e2 )
183 {
184 try
185 {
186 Method method;
187 try
188 {
189 method = type.getMethod( "get", STRING_PARAM );
190 }
191 catch ( NoSuchMethodException e3 )
192 {
193 method = type.getMethod( "get", OBJECT_PARAM );
194 }
195 value = method.invoke( context, new Object[] { property } );
196 }
197 catch ( NoSuchMethodException e3 )
198 {
199 try
200 {
201 Field field = type.getField( property );
202 value = field.get( context );
203 }
204 catch ( NoSuchFieldException e4 )
205 {
206 if ( "length".equals( property ) && type.isArray() )
207 {
208 value = new Integer( Array.getLength( context ) );
209 }
210 else
211 {
212 throw e4;
213 }
214 }
215 }
216 }
217 }
218 }
219 }
220 catch ( Exception e )
221 {
222 value = null;
223 }
224 return value;
225 }
226
227 }