org.apache.taglibs.standard.lang.support.ExpressionEvaluator Maven / Gradle / Ivy
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/*
* Copyright (c) 1997-2020 Oracle and/or its affiliates. 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 org.apache.taglibs.standard.lang.support;
import jakarta.servlet.jsp.JspException;
import jakarta.servlet.jsp.PageContext;
import jakarta.servlet.jsp.tagext.Tag;
/**
* The interface for an expression-language validator and evaluator.
* Classes that implement an expression language expose their functionality
* via this interface.
*
* The validate() 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. No release()
* mechanism or robust lifecycle is specified, for language-interpreter
* pluggability is experimental in EA2.
*
* WARNING: This class supports experimentation for the EA2
* release of JSTL; it is not expected to be part of the final RI or
* specification.
*
* @author Shawn Bayern (based exactly on rev1 draft)
*/
public interface ExpressionEvaluator {
/**
* Translation time validation of an expression.
* This method will return a null String if the expression
* is valid; otherwise an error message.
*/
public String validate(String attributeName,
String expression);
/**
* Evaluates the expression at request time.
*/
public Object evaluate(String attributeName,
String expression,
Class expectedType,
Tag tag,
PageContext pageContext)
throws JspException;
}