org.apache.commons.jexl.ExpressionImpl Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.commons.jexl;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.jexl.parser.SimpleNode;
/**
* Instances of ExpressionImpl are created by the {@link ExpressionFactory},
* and this is the default implementation of the {@link Expression} interface.
*
* @since 1.0
* @author Geir Magnusson Jr.
* @version $Id: ExpressionImpl.java 480412 2006-11-29 05:11:23Z bayard $
*/
class ExpressionImpl implements Expression {
/** resolvers called before expression evaluation. */
protected List preResolvers;
/** resolvers called after expression evaluation. */
protected List postResolvers;
/**
* Original expression. This is just a 'snippet', not a valid statement
* (i.e. foo.bar() vs foo.bar();
*/
protected String expression;
/**
* The resulting AST we can call value() on.
*/
protected SimpleNode node;
/**
* do not let this be generally instantiated with a 'new'.
*
* @param expr the expression.
* @param ref the parsed expression.
*/
ExpressionImpl(String expr, SimpleNode ref) {
expression = expr;
node = ref;
}
/**
* {@inheritDoc}
*/
public Object evaluate(JexlContext context) throws Exception {
Object val = null;
/*
* if we have pre resolvers, give them a wack
*/
if (preResolvers != null) {
val = tryResolver(preResolvers, context);
if (val != JexlExprResolver.NO_VALUE) {
return val;
}
}
val = node.value(context);
/*
* if null, call post resolvers
*/
if (val == null && postResolvers != null) {
val = tryResolver(postResolvers, context);
if (val != JexlExprResolver.NO_VALUE) {
return val;
}
}
return val;
}
/**
* Tries the resolvers in the given resolverlist against the context.
*
* @param resolverList list of JexlExprResolvers
* @param context JexlContext to use for evauluation
* @return value (including null) or JexlExprResolver.NO_VALUE
*/
protected Object tryResolver(List resolverList, JexlContext context) {
Object val = JexlExprResolver.NO_VALUE;
String expr = getExpression();
for (int i = 0; i < resolverList.size(); i++) {
JexlExprResolver jer = (JexlExprResolver) resolverList.get(i);
val = jer.evaluate(context, expr);
/*
* as long as it's not NO_VALUE, return it
*/
if (val != JexlExprResolver.NO_VALUE) {
return val;
}
}
return val;
}
/**
* {@inheritDoc}
*/
public String getExpression() {
return expression;
}
/**
* {@inheritDoc}
*/
public void addPreResolver(JexlExprResolver resolver) {
if (preResolvers == null) {
preResolvers = new ArrayList();
}
preResolvers.add(resolver);
}
/**
* {@inheritDoc}
*/
public void addPostResolver(JexlExprResolver resolver) {
if (postResolvers == null) {
postResolvers = new ArrayList();
}
postResolvers.add(resolver);
}
/**
* Provide a string representation of the expression.
*
* @return the expression or blank if it's null.
*/
public String toString() {
String expr = getExpression();
return expr == null ? "" : expr;
}
}