org.springframework.webflow.core.DefaultExpressionParserFactory 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.core;
import org.springframework.binding.expression.ExpressionParser;
/**
* Static helper factory that creates instances of the default expression parser
* used by Spring Web Flow when requested. Marked final with a private
* constructor to prevent subclassing.
*
* The default is an OGNL based expression parser. Also asserts that OGNL is in
* the classpath when this class is loaded.
*
* @author Keith Donald
*/
public final class DefaultExpressionParserFactory {
/**
* The singleton instance.
*/
private static ExpressionParser INSTANCE;
// static factory - not instantiable
private DefaultExpressionParserFactory() {
}
/**
* Returns the default expression parser. The returned expression parser is
* a thread-safe object.
* @return the expression parser
*/
public static synchronized ExpressionParser getExpressionParser() {
if (INSTANCE == null) {
INSTANCE = createDefaultExpressionParser();
}
return INSTANCE;
}
/**
* Create the default expression parser.
* @return the default expression parser
*/
private static ExpressionParser createDefaultExpressionParser() {
try {
Class.forName("ognl.Ognl");
return new WebFlowOgnlExpressionParser();
} catch (ClassNotFoundException e) {
throw new IllegalStateException(
"Unable to load the default expression parser: OGNL could not be found in the classpath. "
+ "Please add OGNL 2.x to your classpath or set the default ExpressionParser instance to something that is in the classpath. "
+ "Details: " + e.getMessage());
} catch (NoClassDefFoundError e) {
throw new IllegalStateException(
"Unable to construct the default expression parser: ognl.Ognl could not be instantiated. "
+ "Please add OGNL 2.x to your classpath or set the default ExpressionParser instance to something that is in the classpath. "
+ "Details: " + e);
}
}
}