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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.resolver;
17  
18  import org.apache.commons.jexl.JexlExprResolver;
19  import org.apache.commons.jexl.JexlContext;
20  
21  /***
22   *  Simple resolver to try the expression as-is from the context.
23   *
24   *  For example, you could resolve ant-ish properties (foo.bar.woogie)
25   *  using this...
26   *
27   *  hint, hint...
28   *
29   *  @since 1.0
30   *  @author <a href="mailto:geirm@adeptra.com">Geir Magnusson Jr.</a>
31   *  @version $Id: FlatResolver.java 397542 2006-04-27 13:43:47Z dion $
32   */
33  public class FlatResolver implements JexlExprResolver {
34      /***
35       *  Flag to return NO_VALUE on null from context.
36       *  this allows jexl to try to evaluate
37       */
38      protected boolean noValOnNull = true;
39  
40      /***
41       * Default CTOR.
42       */
43      public FlatResolver() {
44      }
45  
46      /***
47       *  CTOR that lets you override the default behavior of
48       *  noValOnNull, which is true. (jexl gets a shot after if null)
49       *
50       *  @param valOnNull Whether NO_VALUE will be returned instead of null.
51       */
52      public FlatResolver(boolean valOnNull) {
53          noValOnNull = valOnNull;
54      }
55  
56      /***
57       *  Try to resolve expression as-is.
58       *
59       *  @param context The context for resolution.
60       *  @param expression The flat expression.
61       *  @return The resolved value.
62       */
63      public Object evaluate(JexlContext context, String expression) {
64          Object val = context.getVars().get(expression);
65  
66          if (val == null && noValOnNull) {
67              return JexlExprResolver.NO_VALUE;
68          }
69  
70          return val;
71      }
72  }