/*
* Copyright 2001-2004 The Apache Software Foundation.
*
* 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.apache.commons.betwixt.expression;
import java.util.Collection;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import org.apache.commons.collections.iterators.ArrayIterator;
import org.apache.commons.collections.iterators.EnumerationIterator;
/** <p><code>IteratorExpression</code> returns an iterator over the current context.</p>
*
* @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
* @version $Revision: 1.8 $
*/
public class IteratorExpression implements Expression {
/** Use this <code>Expression</code> to perform initial evaluation*/
private Expression expression;
/**
* Construct <code>IteratorExpression</code> using given expression for initial evaluation.
* @param expression this expression will be evaluated and the result converted to an
* iterator.
*/
public IteratorExpression(Expression expression) {
this.expression = expression;
}
/**
* Returns an interator over the current context
* @see org.apache.commons.betwixt.expression.Expression
*/
public Object evaluate(Context context) {
// evaluate wrapped expression against context
Object value = expression.evaluate( context );
// based on the class of the result,
// return an appropriate iterator
if ( value instanceof Iterator ) {
// if the value is an iterator, we're done
return (Iterator) value;
} else if ( value instanceof Collection ) {
// if it's a collection, return an iterator for that collection
Collection collection = (Collection) value;
return collection.iterator();
} else if ( value instanceof Map ) {
// if it's a map, return an iterator for the map entries
Map map = (Map) value;
return map.entrySet().iterator();
} else if ( value instanceof Enumeration ) {
// if it's an enumeration, wrap it in an EnumerationIterator
return new EnumerationIterator( (Enumeration) value );
} else if ( value != null ) {
// if we have an array return an ArrayIterator
Class type = value.getClass();
if ( type.isArray() ) {
return new ArrayIterator( value );
}
}
// we've got something we can't deal with
// so return an empty iterator
return Collections.EMPTY_LIST.iterator();
}
/**
* Do nothing
* @see org.apache.commons.betwixt.expression.Expression
*/
public void update(Context context, String newValue) {
// do nothing
}
/**
* Returns something useful for logging
* @return string useful for logging
*/
public String toString() {
return "IteratorExpression [expression=" + expression + "]";
}
}