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1   /*
2    * Copyright 2002-2006 The Apache Software Foundation.
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 org.apache.commons.jexl;
17  
18  /***
19   *  A Resolver allows custom resolution of the expression, and can be
20   *  added in front of the jexl engine, or after in the evaluation.
21   *
22   *  @todo This needs to be explained in detail.  Why do this?
23   *  @since 1.0
24   *  @author <a href="mailto:geirm@adeptra.com">Geir Magnusson Jr.</a>
25   *  @version $Id: JexlExprResolver.java 397092 2006-04-26 05:11:28Z dion $
26   */
27  public interface JexlExprResolver {
28      /*** represents an expression result of no value. */ 
29      Object NO_VALUE = new Object();
30  
31      /***
32       *  Evaluates an expression against the context.
33       *
34       *  @todo Must detail the expectations and effects of this resolver.
35       *  @param context current data context
36       *  @param expression expression to evauluate
37       *  @return value (may be null) or the NO_VALUE object to
38       *       indicate no resolution.
39       */
40      Object evaluate(JexlContext context, String expression);
41  }