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java/org/apache/jasper/compiler/ELInterpreterFactory.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.jasper.compiler;
+
+import javax.servlet.ServletContext;
+
+import org.apache.jasper.JspCompilationContext;
+
+/**
+ * Provides {@link ELInterpreter} instances for JSP compilation.
+ *
+ * The search order is as follows:
+ * <ol>
+ * <li>ELInterpreter instance or implementation class name provided as a
+ *     ServletContext attribute</li>
+ * <li>Implementation class named in a ServletContext initialisation parameter
+ *     </li>
+ * <li>Default implementation</li>
+ * </ol>
+ */
+public class ELInterpreterFactory {
+
+    public static final String EL_INTERPRETER_CLASS_NAME =
+            ELInterpreter.class.getName();
+
+    private static final ELInterpreter DEFAULT_INSTANCE =
+            new DefaultELInterpreter();
+
+
+    /**
+     * Obtain the correct EL Interpreter for the given web application.
+     * @param context The Servlet context
+     * @return the EL interpreter
+     * @throws Exception If an error occurs creating the interpreter
+     */
+    public static ELInterpreter getELInterpreter(ServletContext context)
+            throws Exception {
+
+        ELInterpreter result = null;
+
+        // Search for an implementation
+        // 1. ServletContext attribute (set by application or cached by a
+        //    previous call to this method).
+        Object attribute = context.getAttribute(EL_INTERPRETER_CLASS_NAME);
+        if (attribute instanceof ELInterpreter) {
+            return (ELInterpreter) attribute;
+        } else if (attribute instanceof String) {
+            result = createInstance(context, (String) attribute);
+        }
+
+        // 2. ServletContext init parameter
+        if (result == null) {
+            String className =
+                    context.getInitParameter(EL_INTERPRETER_CLASS_NAME);
+            if (className != null) {
+                result = createInstance(context, className);
+            }
+        }
+
+        // 3. Default
+        if (result == null) {
+            result = DEFAULT_INSTANCE;
+        }
+
+        // Cache the result for next time
+        context.setAttribute(EL_INTERPRETER_CLASS_NAME, result);
+        return result;
+    }
+
+
+    private static ELInterpreter createInstance(ServletContext context,
+            String className) throws Exception {
+        return (ELInterpreter) context.getClassLoader().loadClass(
+                    className).getConstructor().newInstance();
+    }
+
+
+    private ELInterpreterFactory() {
+        // Utility class. Hide default constructor.
+    }
+
+
+    public static class DefaultELInterpreter implements ELInterpreter {
+
+        @Override
+        public String interpreterCall(JspCompilationContext context,
+                boolean isTagFile, String expression,
+                Class<?> expectedType, String fnmapvar) {
+            return JspUtil.interpreterCall(isTagFile, expression, expectedType,
+                    fnmapvar);
+        }
+    }
+}