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/*
 * Copyright 2002-2006 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.webflow.action;

import org.springframework.binding.expression.EvaluationContext;
import org.springframework.binding.expression.Expression;
import org.springframework.util.Assert;
import org.springframework.webflow.execution.Event;
import org.springframework.webflow.execution.RequestContext;

/**
 * An action that evaluates an expression and optionally exposes its result.
 * 

* Delegates to a helper {@link ResultEventFactorySelector} strategy to determine how * to map the evaluation result to an action outcome {@link Event}. * * @see Expression * @see ActionResultExposer * @see ResultEventFactorySelector * * @author Keith Donald */ public class EvaluateAction extends AbstractAction { /** * The expression to evaluate when this action is invoked. Required. */ private Expression expression; /** * The helper that will expose the expression evaluation result. Optional. */ private ActionResultExposer evaluationResultExposer; /** * The selector for the factory that will create the action result event * callers can respond to. */ private ResultEventFactorySelector resultEventFactorySelector = new ResultEventFactorySelector(); /** * Create a new evaluate action. * @param expression the expression to evaluate */ public EvaluateAction(Expression expression) { this(expression, null); } /** * Create a new evaluate action. * @param expression the expression to evaluate * @param evaluationResultExposer the strategy for how the expression result * will be exposed to the flow */ public EvaluateAction(Expression expression, ActionResultExposer evaluationResultExposer) { Assert.notNull(expression, "The expression this action should evaluate is required"); this.expression = expression; this.evaluationResultExposer = evaluationResultExposer; } protected Event doExecute(RequestContext context) throws Exception { Object result = expression.evaluate(context, getEvaluationContext(context)); if (evaluationResultExposer != null) { evaluationResultExposer.exposeResult(result, context); } return resultEventFactorySelector.forResult(result).createResultEvent(this, result, context); } /** * Template method subclasses may override to customize the expressin * evaluation context. This implementation returns null. * @param context the request context * @return the evaluation context */ protected EvaluationContext getEvaluationContext(RequestContext context) { return null; } }





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