ExpressionEvaluator


1   /*
2    * Copyright 1999-2004 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  
17  package org.apache.taglibs.standard.lang.support;
18  
19  import javax.servlet.jsp.JspException  ;
20  import javax.servlet.jsp.PageContext  ;
21  import javax.servlet.jsp.tagext.Tag  ;
22  
23  /**
24   * <p>The interface for an expression-language validator and evaluator.
25   * Classes that implement an expression language expose their functionality
26   * via this interface.</p>
27   *
28   * <p>The validate() and evaluate() methods must be thread-safe.  That is,
29   * multiple threads may call these methods on the same ExpressionEvaluator
30   * object simultaneously.  Implementations should synchronize access if
31   * they depend on transient state.  Implementations should not, however,
32   * assume that only one object of each ExpressionEvaluator type will be
33   * instantiated; global caching should therefore be static.  No release()
34   * mechanism or robust lifecycle is specified, for language-interpreter
35   * pluggability is experimental in EA2.</p>
36   *
37   * <p><b>WARNING</b>:  This class supports experimentation for the EA2
38   * release of JSTL; it is not expected to be part of the final RI or
39   * specification.</p>
40   *
41   * @author Shawn Bayern (based exactly on rev1 draft)
42   */
43  public interface ExpressionEvaluator {
44  
45      /** 
46       * Translation time validation of an expression. 
47       * This method will return a null String if the expression 
48       * is valid; otherwise an error message. 
49       */ 
50      public String   validate(String   attributeName, 
51                             String   expression); 
52  
53      /** 
54       * Evaluates the expression at request time. 
55       */ 
56      public Object   evaluate(String   attributeName, 
57                             String   expression, 
58                             Class   expectedType, 
59                             Tag   tag, 
60                             PageContext   pageContext) 
61         throws JspException  ; 
62  } 
63
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Popular Tags