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Java > Open Source Codes > org > apache > commons > jelly > expression > Expression


1 /*
2  * Copyright 2002,2004 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.jelly.expression;
17
18 import java.util.Iterator JavaDoc;
19
20 import org.apache.commons.jelly.JellyContext;
21
22 /** <p><code>Expression</code> represents an arbitrary expression using some pluggable
23   * expression language.</p>
24   *
25   * @author <a HREF="mailto:jstrachan@apache.org">James Strachan</a>
26   * @version $Revision: 155420 $
27   */
28 public interface Expression {
29
30     /**
31      * @return the textual representation of this expression
32      */
33     public String JavaDoc getExpressionText();
34
35     /**
36      * Evaluates the expression with the given context
37      * and returns the result
38      */
39     public Object JavaDoc evaluate(JellyContext context);
40
41     /**
42      * Evaluates the expression with the given context
43      * coercing the result to be a String.
44      */
45     public String JavaDoc evaluateAsString(JellyContext context);
46
47     /**
48      * Evaluates the expression with the given context
49      * coercing the result to be a boolean.
50      */
51     public boolean evaluateAsBoolean(JellyContext context);
52
53     /**
54      * Evaluates the expression with the given context
55      * coercing the result to be an Iterator.
56      */
57     public Iterator JavaDoc evaluateAsIterator(JellyContext context);
58
59     /**
60      * This method evaluates the expression until a value (a non-Expression) object
61      * is returned.
62      * If the expression returns another expression, then the nested expression is evaluated.
63      * <p>
64      * Sometimes when Jelly is used inside Maven the value
65      * of an expression can actually be another expression.
66      * For example if a properties file is read, the values of variables
67      * can actually be expressions themselves.
68      * <p>
69      * e.g. ${foo.bar} can lookup "foo.bar" in a Maven context
70      * which could actually be another expression.
71      * <p>
72      * So using this method, nested expressions can be evaluated to the
73      * actual underlying value object.
74      */
75     public Object JavaDoc evaluateRecurse(JellyContext context);
76 }
77
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