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1   package org.codehaus.plexus.interpolation;
2   
3   import java.util.List;
4   
5   /*
6    * Copyright 2001-2008 Codehaus Foundation.
7    *
8    * Licensed under the Apache License, Version 2.0 (the "License");
9    * you may not use this file except in compliance with the License.
10   * 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, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  
21  /**
22   * Supplies one strategy for resolving a value for an interpolation expression.
23   * ValueSources may be stacked.
24   */
25  public interface ValueSource
26  {
27  
28      /**
29       * @param expression The string expression.
30       * @return the value related to the expression, or null if not found.
31       */
32      public Object getValue( String expression );
33  
34      /**
35       * Return the feedback about resolution failures for a particular expression.
36       *
37       * @return a combination of String and Throwable instances, where strings
38       * related to throwables are listed first.
39       */
40      List getFeedback();
41  
42      /**
43       * Clear the feedback accumulated by a prior interpolation run.
44       */
45      void clearFeedback();
46  }