Source Code Cross Referenced for ExpressionEvaluator.java in  » Sevlet-Container » apache-tomcat-6.0.14 » javax » servlet » jsp » el » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Sevlet Container » apache tomcat 6.0.14 » javax.servlet.jsp.el 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Licensed to the Apache Software Foundation (ASF) under one or more
003:         * contributor license agreements.  See the NOTICE file distributed with
004:         * this work for additional information regarding copyright ownership.
005:         * The ASF licenses this file to You under the Apache License, Version 2.0
006:         * (the "License"); you may not use this file except in compliance with
007:         * the License.  You may obtain a copy of the License at
008:         *
009:         *     http://www.apache.org/licenses/LICENSE-2.0
010:         *
011:         * Unless required by applicable law or agreed to in writing, software
012:         * distributed under the License is distributed on an "AS IS" BASIS,
013:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014:         * See the License for the specific language governing permissions and
015:         * limitations under the License.
016:         */
017:
018:        package javax.servlet.jsp.el;
019:
020:        /**
021:         * <p>The abstract base class for an expression-language evaluator.
022:         * Classes that implement an expression language expose their functionality
023:         * via this abstract class.</p>
024:         *
025:         * <p>An instance of the ExpressionEvaluator can be obtained via the 
026:         * JspContext / PageContext</p>
027:         *
028:         * <p>The parseExpression() and evaluate() methods must be thread-safe.  
029:         * That is, multiple threads may call these methods on the same 
030:         * ExpressionEvaluator object simultaneously.  Implementations should 
031:         * synchronize access if they depend on transient state.  Implementations 
032:         * should not, however, assume that only one object of each 
033:         * ExpressionEvaluator type will be instantiated; global caching should 
034:         * therefore be static.</p>
035:         *
036:         * <p>Only a single EL expression, starting with '${' and ending with
037:         * '}', can be parsed or evaluated at a time.  EL expressions 
038:         * cannot be mixed with static text.  For example, attempting to 
039:         * parse or evaluate "<code>abc${1+1}def${1+1}ghi</code>" or even
040:         * "<code>${1+1}${1+1}</code>" will cause an <code>ELException</code> to
041:         * be thrown.</p>
042:         *
043:         * <p>The following are examples of syntactically legal EL expressions:
044:         *
045:         * <ul>
046:         *   <li><code>${person.lastName}</code></li>
047:         *   <li><code>${8 * 8}</code></li>
048:         *   <li><code>${my:reverse('hello')}</code></li>
049:         * </ul>
050:         * </p>
051:         *
052:         * @since 2.0
053:         * @deprecated
054:         */
055:        public abstract class ExpressionEvaluator {
056:
057:            /**
058:             * Prepare an expression for later evaluation.  This method should perform
059:             * syntactic validation of the expression; if in doing so it detects 
060:             * errors, it should raise an ELParseException.
061:             *
062:             * @param expression The expression to be evaluated.
063:             * @param expectedType The expected type of the result of the evaluation
064:             * @param fMapper A FunctionMapper to resolve functions found in 
065:             *     the expression.  It can be null, in which case no functions 
066:             *     are supported for this invocation.  The ExpressionEvaluator 
067:             *     must not hold on to the FunctionMapper reference after 
068:             *     returning from <code>parseExpression()</code>.  The 
069:             *     <code>Expression</code> object returned must invoke the same 
070:             *     functions regardless of whether the mappings in the 
071:             *     provided <code>FunctionMapper</code> instance change between 
072:             *     calling <code>ExpressionEvaluator.parseExpression()</code>
073:             *     and <code>Expression.evaluate()</code>.
074:             * @return The Expression object encapsulating the arguments.
075:             *
076:             * @exception ELException Thrown if parsing errors were found.
077:             */
078:            public abstract Expression parseExpression(String expression,
079:                    Class expectedType, FunctionMapper fMapper)
080:                    throws ELException;
081:
082:            /** 
083:             * Evaluates an expression.  This method may perform some syntactic 
084:             * validation and, if so, it should raise an ELParseException error if 
085:             * it encounters syntactic errors.  EL evaluation errors should cause 
086:             * an ELException to be raised.
087:             *
088:             * @param expression The expression to be evaluated.
089:             * @param expectedType The expected type of the result of the evaluation
090:             * @param vResolver A VariableResolver instance that can be used at 
091:             *     runtime to resolve the name of implicit objects into Objects.
092:             * @param fMapper A FunctionMapper to resolve functions found in 
093:             *     the expression.  It can be null, in which case no functions 
094:             *     are supported for this invocation.  
095:             * @return The result of the expression evaluation.
096:             *
097:             * @exception ELException Thrown if the expression evaluation failed.
098:             */
099:            public abstract Object evaluate(String expression,
100:                    Class expectedType, VariableResolver vResolver,
101:                    FunctionMapper fMapper) throws ELException;
102:        }
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