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java/javax/servlet/jsp/el/ExpressionEvaluator.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 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}${1+1}</code>" will
+ * cause an <code>ELException</code> to be thrown.
+ * </p>
+ * <p>
+ * The following are examples of syntactically legal EL expressions:
+ * </p>
+ * <ul>
+ * <li><code>${person.lastName}</code></li>
+ * <li><code>${8 * 8}</code></li>
+ * <li><code>${my:reverse('hello')}</code></li>
+ * </ul>
+ *
+ * @since 2.0
+ * @deprecated As of JSP 2.1, replaced by javax.el.ExpressionFactory
+ */
+@SuppressWarnings("dep-ann")
+// TCK signature test fails with annotation
+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,
+            @SuppressWarnings("rawtypes")// TCK signature fails with generics
+            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,
+            @SuppressWarnings("rawtypes")// TCK signature fails with generics
+            Class expectedType, VariableResolver vResolver,
+            FunctionMapper fMapper) throws ELException;
+}