/*
* Copyright (c) 2002-2012 Alibaba Group Holding Limited.
* All rights reserved.
*
* 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.alibaba.citrus.expr.jexl;
import com.alibaba.citrus.expr.Expression;
import com.alibaba.citrus.expr.ExpressionContext;
import com.alibaba.citrus.expr.ExpressionFactory;
import com.alibaba.citrus.expr.ExpressionParseException;
import com.alibaba.citrus.expr.support.ExpressionSupport;
import org.apache.commons.jexl2.JexlEngine;
/**
* 创建<code>JexlExpression</code>的工厂。
*
* @author Michael Zhou
*/
public class JexlExpressionFactory implements ExpressionFactory {
private final JexlEngine engine = new JexlEngine();
/** 是否支持context变量，就是用小数点分隔的变量名。 */
private boolean supportContextVariables = true;
/**
* 是否支持context变量，就是用小数点分隔的变量名。
*
* @return 如果支持，则返回<code>true</code>
*/
public boolean isSupportContextVariables() {
return supportContextVariables;
}
/**
* 设置支持context变量。
*
* @param supportContextVariables 是否支持context变量
*/
public void setSupportContextVariables(boolean supportContextVariables) {
this.supportContextVariables = supportContextVariables;
}
/**
* 创建表达式。
*
* @param expr 表达式字符串
* @return 表达式
*/
public Expression createExpression(final String expr) throws ExpressionParseException {
final Expression jexlExpression;
try {
jexlExpression = new JexlExpression(engine.createExpression(expr));
} catch (Exception e) {
throw new ExpressionParseException(e);
}
if (isSupportContextVariables() && isValidContextVariableName(expr)) {
return new ExpressionSupport() {
/**
* 取得表达式字符串表示。
*
* @return 表达式字符串表示
*/
public String getExpressionText() {
return expr;
}
/**
* 在指定的上下文中计算表达式。
*
* @param context <code>ExpressionContext</code>上下文
* @return 表达式的计算结果
*/
public Object evaluate(ExpressionContext context) {
// 首先执行jexl表达式
Object value = jexlExpression.evaluate(context);
// 如果jexl表达式结果为null，则从context中直接取值
if (value == null) {
value = context.get(expr);
}
return value;
}
};
}
return jexlExpression;
}
/**
* 判断是否为context变量。
*
* @return 如果是，则返回<code>true</code>
*/
protected boolean isValidContextVariableName(String varName) {
for (int i = 0; i < varName.length(); i++) {
char ch = varName.charAt(i);
if (Character.isWhitespace(ch) || ch == '[') {
return false;
}
}
return true;
}
}