1 /* ***************************************************************************
2 * Copyright (c) 2008 Brabenetz Harald, Austria.
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
18 package org.settings4j.util;
19
20 import java.util.Map;
21
22 import org.apache.taglibs.standard.lang.jstl.ELEvaluator;
23 import org.apache.taglibs.standard.lang.jstl.ELException;
24 import org.apache.taglibs.standard.lang.jstl.VariableResolver;
25
26
27 /**
28 * A Simple Variable Resolver for ExpressionLanguage. With the JSTLVariableResolver you need a PageContext-Object with
29 * HttpRequest etc.... This class is a Simple Variant of the JSTLVariableResolver who accept a Simple Map as
30 * PageContext. Example: 1. create a Map with Values(key="name", value="Herr Mustermann") 2. parse the String
31 * "Hello, ${name}" with the given Map 3. result: "Hello, Herr Mustermann".
32 *
33 * @see org.apache.taglibs.standard.lang.jstl.JSTLVariableResolver
34 * @author Harald.Brabenetz
35 */
36 public final class ExpressionLanguageUtil {
37
38 /** Hide Constructor (Utility Pattern).*/
39 private ExpressionLanguageUtil() {
40 super();
41 }
42 /**
43 * The VariableResolver for a <code>java.util.Map</code> as Context-Object.
44 */
45 private static final VariableResolver SIMPLE_VARIABLE_RESOLVER = new VariableResolver() {
46
47 /**
48 * Resolves the specified variable within the given context. Returns null if the variable is not found.
49 **/
50 public Object resolveVariable(final String pName, final Object simpleMap) {
51 final Map ctx = (Map) simpleMap;
52 return ctx.get(pName);
53 }
54 };
55
56 private static final ELEvaluator SIMPLE_EVALUATOR = new ELEvaluator(SIMPLE_VARIABLE_RESOLVER);
57
58 /**
59 * Helper-Function to evaluate a Expression to a String.
60 *
61 * @param expression The Expression to be evaluated
62 * @param context The context where the expression has Access
63 * @return The Result as String
64 * @throws ELException Throw an Exception if the expression is not valid.
65 */
66 public static String evaluateExpressionLanguage(final String expression, final Map context) throws ELException {
67 return (String) evaluateExpressionLanguage(expression, context, String.class);
68 }
69
70 /**
71 * Helper-Function to evaluate a Expression to a given Class.
72 *
73 * @param expression The Expression to be evaluated
74 * @param context The context where the expression has Access
75 * @param returnType the Class-Object who will be returned
76 * @return The Result as the given return-Type
77 * @throws ELException Throw an Exception if the expression is not valid.
78 */
79 public static Object evaluateExpressionLanguage(final String expression, final Map context, final Class returnType)
80 throws ELException {
81 return SIMPLE_EVALUATOR.evaluate(expression, context, returnType, null, null);
82 }
83
84 }