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Jetty example source code file (ExpressionEvaluator.java)

This example Jetty source code file (ExpressionEvaluator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Jetty tags/keywords

class, class, elexception, elexception, expression, expressionevaluator, functionmapper, functionmapper, object, string, string, variableresolver

The Jetty ExpressionEvaluator.java source code

/**
 *
 * Copyright 2003-2004 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.
 */

//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//

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${1+1}ghi" or even
 * "<code>${1+1}${1+1}" will cause an ELException to
 * be thrown.</p>
 *
 * <p>The following are examples of syntactically legal EL expressions:
 *
 * <ul>
 *   <li>${person.lastName}
 *   <li>${8 * 8}
 *   <li>${my:reverse('hello')}
 * </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().  The 
     *     <code>Expression object returned must invoke the same 
     *     functions regardless of whether the mappings in the 
     *     provided <code>FunctionMapper instance change between 
     *     calling <code>ExpressionEvaluator.parseExpression()
     *     and <code>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; 
}

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