org.springframework.webflow.engine.support.BooleanExpressionTransitionCriteria Maven / Gradle / Ivy
/*
* 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.engine.support;
import java.util.HashMap;
import java.util.Map;
import org.springframework.binding.expression.EvaluationContext;
import org.springframework.binding.expression.Expression;
import org.springframework.util.Assert;
import org.springframework.webflow.engine.TransitionCriteria;
import org.springframework.webflow.execution.RequestContext;
/**
* Transition criteria that tests the value of an expression. The
* expression is used to express a condition that guards transition
* execution in a web flow. Expressions will be evaluated agains the request
* context and should return a boolean result.
*
* @author Keith Donald
* @author Erwin Vervaet
*/
public class BooleanExpressionTransitionCriteria implements TransitionCriteria {
/**
* Constant alias that points to the id of the last event that occured
* in a web flow execution.
*/
private static final String RESULT_ALIAS = "result";
/**
* The expression evaluator to use.
*/
private Expression booleanExpression;
/**
* Create a new expression based transition criteria object.
* @param booleanExpression the expression evaluator testing the criteria,
* this expression should be a condition that returns a Boolean value
*/
public BooleanExpressionTransitionCriteria(Expression booleanExpression) {
Assert.notNull(booleanExpression, "The expression to test is required");
this.booleanExpression = booleanExpression;
}
public boolean test(RequestContext context) {
Object result = booleanExpression.evaluate(context, getEvaluationContext(context));
Assert.isInstanceOf(Boolean.class, result, "Impossible to determine result of boolean expression: ");
return ((Boolean)result).booleanValue();
}
/**
* Setup a context with a few aliased values to make writing expression based
* transition conditions a bit easier.
*/
protected EvaluationContext getEvaluationContext(RequestContext context) {
final Map attributes = new HashMap(1, 1);
// ${#result == lastEvent.id}
if (context.getLastEvent() != null) {
attributes.put(RESULT_ALIAS, context.getLastEvent().getId());
}
return new EvaluationContext() {
public Map getAttributes() {
return attributes;
}
};
}
public String toString() {
return booleanExpression.toString();
}
}