1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.jasper.compiler;
18
19 import javax.servlet.ServletContext;
20
21 import org.apache.jasper.JspCompilationContext;
22
23 /**
24 * Provides {@link ELInterpreter} instances for JSP compilation.
25 *
26 * The search order is as follows:
27 * <ol>
28 * <li>ELInterpreter instance or implementation class name provided as a
29 * ServletContext attribute</li>
30 * <li>Implementation class named in a ServletContext initialisation parameter
31 * </li>
32 * <li>Default implementation</li>
33 * </ol>
34 */
35 public class ELInterpreterFactory {
36
37 public static final String EL_INTERPRETER_CLASS_NAME =
38 ELInterpreter.class.getName();
39
40 private static final ELInterpreter DEFAULT_INSTANCE =
41 new DefaultELInterpreter();
42
43
44 /**
45 * Obtain the correct EL Interpreter for the given web application.
46 * @param context The Servlet context
47 * @return the EL interpreter
48 * @throws Exception If an error occurs creating the interpreter
49 */
50 public static ELInterpreter getELInterpreter(ServletContext context)
51 throws Exception {
52
53 ELInterpreter result = null;
54
55 // Search for an implementation
56 // 1. ServletContext attribute (set by application or cached by a
57 // previous call to this method).
58 Object attribute = context.getAttribute(EL_INTERPRETER_CLASS_NAME);
59 if (attribute instanceof ELInterpreter) {
60 return (ELInterpreter) attribute;
61 } else if (attribute instanceof String) {
62 result = createInstance(context, (String) attribute);
63 }
64
65 // 2. ServletContext init parameter
66 if (result == null) {
67 String className =
68 context.getInitParameter(EL_INTERPRETER_CLASS_NAME);
69 if (className != null) {
70 result = createInstance(context, className);
71 }
72 }
73
74 // 3. Default
75 if (result == null) {
76 result = DEFAULT_INSTANCE;
77 }
78
79 // Cache the result for next time
80 context.setAttribute(EL_INTERPRETER_CLASS_NAME, result);
81 return result;
82 }
83
84
85 private static ELInterpreter createInstance(ServletContext context,
86 String className) throws Exception {
87 return (ELInterpreter) context.getClassLoader().loadClass(
88 className).getConstructor().newInstance();
89 }
90
91
92 private ELInterpreterFactory() {
93 // Utility class. Hide default constructor.
94 }
95
96
97 public static class DefaultELInterpreter implements ELInterpreter {
98
99 @Override
100 public String interpreterCall(JspCompilationContext context,
101 boolean isTagFile, String expression,
102 Class<?> expectedType, String fnmapvar) {
103 return JspUtil.interpreterCall(isTagFile, expression, expectedType,
104 fnmapvar);
105 }
106 }
107 }
108