Expression


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  
17  package org.apache.commons.jexl;
18  
19  
20  /**
21   * <p>
22   * Represents a single JEXL expression.  This simple interface
23   * provides access to the underlying expression through getExpression(),
24   * and it provides hooks to add a pre- and post- expression resolver.
25   * </p>
26   *
27   * <p>
28   * An expression is different than a script - it is simply a reference of
29   * an expression.
30   * </p>
31   *
32   * @since 1.0
33   * @author <a HREF="mailto:geirm@apache.org">Geir Magnusson Jr.</a>
34   * @version $Id: Expression.java 397092 2006-04-26 05:11:28Z dion $
35   */
36  public interface Expression {
37      /**
38       * Evaluates the expression with the variables contained in the
39       * supplied {@link JexlContext}.
40       *
41       * @param context A JexlContext containing variables.
42       * @return The result of this evaluation
43       * @throws Exception on any error
44       */
45      Object   evaluate(JexlContext context) throws Exception  ;
46  
47      /**
48       * Returns the JEXL expression this Expression was created with.
49       *
50       * @return The JEXL expression to be evaluated
51       */
52      String   getExpression();
53  
54      /**
55       * Allows addition of a resolver to allow custom interdiction of
56       * expression evaluation.
57       *
58       * @param resolver resolver to be called before Jexl expression evaluated
59       */
60      void addPreResolver(JexlExprResolver resolver);
61  
62      /**
63       * Allows addition of a resolver to allow custom interdiction of
64       * expression evaluation.
65       *
66       * @param resolver resolver to be called if Jexl expression
67       *  evaluated to null.
68       */
69      void addPostResolver(JexlExprResolver resolver);
70  }
71
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