Java tutorial
/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER. * * Copyright (c) 1997-2010 Oracle and/or its affiliates. All rights reserved. * * The contents of this file are subject to the terms of either the GNU * General Public License Version 2 only ("GPL") or the Common Development * and Distribution License("CDDL") (collectively, the "License"). You * may not use this file except in compliance with the License. You can * obtain a copy of the License at * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html * or packager/legal/LICENSE.txt. See the License for the specific * language governing permissions and limitations under the License. * * When distributing the software, include this License Header Notice in each * file and include the License file at packager/legal/LICENSE.txt. * * GPL Classpath Exception: * Oracle designates this particular file as subject to the "Classpath" * exception as provided by Oracle in the GPL Version 2 section of the License * file that accompanied this code. * * Modifications: * If applicable, add the following below the License Header, with the fields * enclosed by brackets [] replaced by your own identifying information: * "Portions Copyright [year] [name of copyright owner]" * * Contributor(s): * If you wish your version of this file to be governed by only the CDDL or * only the GPL Version 2, indicate your decision by adding "[Contributor] * elects to include this software in this distribution under the [CDDL or GPL * Version 2] license." If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. * * * This file incorporates work covered by the following copyright and * permission notice: * * Copyright 2004 The Apache Software Foundation * * Licensed 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 javax.servlet.jsp.el; /** * <p>The abstract base class for an expression-language evaluator. * Classes that implement an expression language expose their functionality * via this abstract class.</p> * * <p>An instance of the ExpressionEvaluator can be obtained via the * JspContext / PageContext</p> * * <p>The parseExpression() and evaluate() methods must be thread-safe. * That is, multiple threads may call these methods on the same * ExpressionEvaluator object simultaneously. Implementations should * synchronize access if they depend on transient state. Implementations * should not, however, assume that only one object of each * ExpressionEvaluator type will be instantiated; global caching should * therefore be static.</p> * * <p>Only a single EL expression, starting with '${' and ending with * '}', can be parsed or evaluated at a time. EL expressions * cannot be mixed with static text. For example, attempting to * parse or evaluate "<code>abc${1+1}def${1+1}ghi</code>" or even * "<code>${1+1}${1+1}</code>" will cause an <code>ELException</code> to * be thrown.</p> * * <p>The following are examples of syntactically legal EL expressions: * * <ul> * <li><code>${person.lastName}</code></li> * <li><code>${8 * 8}</code></li> * <li><code>${my:reverse('hello')}</code></li> * </ul> * </p> * * @deprecated As of JSP 2.1, replaced by {@link javax.el.ExpressionFactory} * @since JSP 2.0 */ public abstract class ExpressionEvaluator { /** * Prepare an expression for later evaluation. This method should perform * syntactic validation of the expression; if in doing so it detects * errors, it should raise an ELParseException. * * @param expression The expression to be evaluated. * @param expectedType The expected type of the result of the evaluation * @param fMapper A FunctionMapper to resolve functions found in * the expression. It can be null, in which case no functions * are supported for this invocation. The ExpressionEvaluator * must not hold on to the FunctionMapper reference after * returning from <code>parseExpression()</code>. The * <code>Expression</code> object returned must invoke the same * functions regardless of whether the mappings in the * provided <code>FunctionMapper</code> instance change between * calling <code>ExpressionEvaluator.parseExpression()</code> * and <code>Expression.evaluate()</code>. * @return The Expression object encapsulating the arguments. * * @exception ELException Thrown if parsing errors were found. */ public abstract Expression parseExpression(String expression, Class expectedType, FunctionMapper fMapper) throws ELException; /** * Evaluates an expression. This method may perform some syntactic * validation and, if so, it should raise an ELParseException error if * it encounters syntactic errors. EL evaluation errors should cause * an ELException to be raised. * * @param expression The expression to be evaluated. * @param expectedType The expected type of the result of the evaluation * @param vResolver A VariableResolver instance that can be used at * runtime to resolve the name of implicit objects into Objects. * @param fMapper A FunctionMapper to resolve functions found in * the expression. It can be null, in which case no functions * are supported for this invocation. * @return The result of the expression evaluation. * * @exception ELException Thrown if the expression evaluation failed. */ public abstract Object evaluate(String expression, Class expectedType, VariableResolver vResolver, FunctionMapper fMapper) throws ELException; }