jakarta.servlet.jsp.el.ExpressionEvaluator Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2020 Oracle and/or its affiliates and others.
* All rights reserved.
* 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 jakarta.servlet.jsp.el;
/**
*
* The abstract base class for an expression-language evaluator. Classes that implement an expression language expose
* their functionality via this abstract class.
*
*
*
* An instance of the ExpressionEvaluator can be obtained via the JspContext / PageContext
*
*
*
* 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.
*
*
*
* Only a single EL expression, starting with '${' and ending with '}', can be parsed or evaluated at a time. EL
* expressions cannot be mixed with static text. For example, attempting to parse or evaluate
* "abc${1+1}def${1+1}ghi" or even "${1+1}${1+1}" will cause an ELException to be
* thrown.
*
*
*
* The following are examples of syntactically legal EL expressions:
*
*
*
* ${person.lastName}${8 * 8}${my:reverse('hello')}
*
* @deprecated As of JSP 2.1, replaced by {@link jakarta.el.ExpressionFactory}
* @since JSP 2.0
*/
@Deprecated
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 parseExpression(). The
* Expression object returned must invoke the same functions regardless of whether
* the mappings in the provided FunctionMapper instance change between calling
* ExpressionEvaluator.parseExpression() and Expression.evaluate().
* @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;
}