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1   package org.codehaus.plexus.interpolation;
2   
3   /*
4    * Copyright 2007 The Codehaus Foundation.
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * 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  
19  import org.codehaus.plexus.interpolation.reflection.ReflectionValueExtractor;
20  
21  /**
22   * Wraps an object, providing reflective access to the object graph of which the
23   * supplied object is the root. Expressions like 'child.name' will translate into
24   * 'rootObject.getChild().getName()' for non-boolean properties, and
25   * 'rootObject.getChild().isName()' for boolean properties.
26   */
27  public class ObjectBasedValueSource extends AbstractValueSource {
28  
29      private final Object root;
30  
31      /**
32       * Construct a new value source, using the supplied object as the root from
33       * which to start, and using expressions split at the dot ('.') to navigate
34       * the object graph beneath this root.
35       * @param root the root of the graph.
36       */
37      public ObjectBasedValueSource(Object root) {
38          super(true);
39          this.root = root;
40      }
41  
42      /**
43       * <p>Split the expression into parts, tokenized on the dot ('.') character. Then,
44       * starting at the root object contained in this value source, apply each part
45       * to the object graph below this root, using either 'getXXX()' or 'isXXX()'
46       * accessor types to resolve the value for each successive expression part.
47       * Finally, return the result of the last expression part's resolution.</p>
48       *
49       * <p><b>NOTE:</b> The object-graph nagivation actually takes place via the
50       * {@link ReflectionValueExtractor} class.</p>
51       */
52      public Object getValue(String expression) {
53          if (expression == null || expression.trim().length() < 1) {
54              return null;
55          }
56  
57          try {
58              return ReflectionValueExtractor.evaluate(expression, root, false);
59          } catch (Exception e) {
60              addFeedback("Failed to extract \'" + expression + "\' from: " + root, e);
61          }
62  
63          return null;
64      }
65  }