com.seovic.core.expression.SpelExpression.java Source code

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Here is the source code for com.seovic.core.expression.SpelExpression.java

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/*
 * Copyright 2009 Aleksandar Seovic
 *
 * 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 com.seovic.core.expression;

import java.util.Map;

import org.springframework.expression.EvaluationException;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.ParseException;

import org.springframework.expression.spel.standard.SpelExpressionParser;

import org.springframework.expression.spel.support.StandardEvaluationContext;

/**
 * An imlementation of {@link Expression} that evaluates specified expression
 * using <a href="http://static.springsource.org/spring/docs/3.0.x/reference/html/expressions.html" target="_new">
 * Spring Expression Language (SpEL)</a>.
 * 
 * @author Aleksandar Seovic  2009.09.30
 * @author Ivan Cikic  2009.09.30
 */
@SuppressWarnings("unchecked")
public class SpelExpression<T> extends AbstractExpression<T> {
    // ---- constructors ----------------------------------------------------

    /**
     * Deserialization constructor (for internal use only).
     */
    public SpelExpression() {
    }

    /**
     * Construct a <tt>SpelExpression</tt> instance.
      *
      * @param expression  the expression to evaluate
      */
    public SpelExpression(String expression) {
        super(expression);
    }

    // ---- Expression implementation ---------------------------------------

    /**
      * {@inheritDoc}
      */
    public T evaluate(Object target, Map variables) {
        Expression expression = getParsedExpression();
        StandardEvaluationContext context = m_context;

        context.setRootObject(target);
        if (variables != null) {
            context.setVariables(variables);
        }
        try {
            return (T) expression.getValue(context);
        } catch (EvaluationException e) {
            throw new RuntimeException(e);
        }
    }

    /**
      * {@inheritDoc}
      */
    public void evaluateAndSet(Object target, Object value) {
        Expression expression = getParsedExpression();
        StandardEvaluationContext context = m_context;

        context.setRootObject(target);
        try {
            expression.setValue(context, value);
        } catch (EvaluationException e) {
            throw new RuntimeException(e);
        }
    }

    // ---- helper methods --------------------------------------------------

    /**
      * Return a parsed SpEL expression.
      *
      * @return parsed SpEL expression
      */
    protected Expression getParsedExpression() {
        Expression parsedExpression = m_parsedExpression;
        if (parsedExpression == null) {
            try {
                m_parsedExpression = parsedExpression = s_parser.parseExpression(m_expression);
            } catch (ParseException e) {
                throw new IllegalArgumentException("[" + m_expression + "] is not a valid SpEL expression");
            }
        }
        return parsedExpression;
    }

    // ---- data members ----------------------------------------------------

    private static final ExpressionParser s_parser = new SpelExpressionParser();

    private transient StandardEvaluationContext m_context = new StandardEvaluationContext();
    private transient Expression m_parsedExpression;
}