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/*
 * Copyright 2002-2015 the original author or authors.
 *
 * 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.springframework.context.expression;

import java.util.Map;

import org.springframework.expression.Expression;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.util.Assert;
import org.springframework.util.ObjectUtils;

/**
 * Shared utility class used to evaluate and cache SpEL expressions that
 * are defined on {@link java.lang.reflect.AnnotatedElement}.
 *
 * @author Stephane Nicoll
 * @since 4.2.0
 * @see AnnotatedElementKey
 */
public abstract class CachedExpressionEvaluator {

	private final SpelExpressionParser parser;

	/**
	 * Create a new instance with the specified {@link SpelExpressionParser}.
	 */
	protected CachedExpressionEvaluator(SpelExpressionParser parser) {
		Assert.notNull(parser, "Parser must not be null");
		this.parser = parser;
	}

	/**
	 * Create a new instance with a default {@link SpelExpressionParser}.
	 */
	protected CachedExpressionEvaluator() {
		this(new SpelExpressionParser());
	}

	/**
	 * Return the {@link SpelExpressionParser} to use.
	 */
	protected SpelExpressionParser getParser() {
		return this.parser;
	}

	/**
	 * Return the {@link Expression} for the specified SpEL value
	 * 

Parse the expression if it hasn't been already. * @param cache the cache to use * @param elementKey the element on which the expression is defined * @param expression the expression to parse */ protected Expression getExpression(Map cache, AnnotatedElementKey elementKey, String expression) { ExpressionKey expressionKey = createKey(elementKey, expression); Expression expr = cache.get(expressionKey); if (expr == null) { expr = getParser().parseExpression(expression); cache.put(expressionKey, expr); } return expr; } private ExpressionKey createKey(AnnotatedElementKey elementKey, String expression) { return new ExpressionKey(elementKey, expression); } protected static class ExpressionKey { private final AnnotatedElementKey key; private final String expression; protected ExpressionKey(AnnotatedElementKey key, String expression) { this.key = key; this.expression = expression; } @Override public boolean equals(Object other) { if (this == other) { return true; } if (!(other instanceof ExpressionKey)) { return false; } ExpressionKey otherKey = (ExpressionKey) other; return (this.key.equals(otherKey.key) && ObjectUtils.nullSafeEquals(this.expression, otherKey.expression)); } @Override public int hashCode() { return this.key.hashCode() * 29 + (this.expression != null ? this.expression.hashCode() : 0); } } }





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