| /* |
| * 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> |
| * |
| * @since 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; |
| } |
| |