01: /*
02: * Licensed to the Apache Software Foundation (ASF) under one or more
03: * contributor license agreements. See the NOTICE file distributed with
04: * this work for additional information regarding copyright ownership.
05: * The ASF licenses this file to You under the Apache License, Version 2.0
06: * (the "License"); you may not use this file except in compliance with
07: * the License. You may obtain a copy of the License at
08: *
09: * http://www.apache.org/licenses/LICENSE-2.0
10: *
11: * Unless required by applicable law or agreed to in writing, software
12: * distributed under the License is distributed on an "AS IS" BASIS,
13: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14: * See the License for the specific language governing permissions and
15: * limitations under the License.
16: */
17: package org.apache.cocoon.forms.expression;
18:
19: import org.outerj.expression.AbstractExpression;
20: import org.outerj.expression.Expression;
21: import org.outerj.expression.ExpressionContext;
22: import org.outerj.expression.ExpressionException;
23:
24: /**
25: * Returns true if argument is null.
26: *
27: * @version $Id: IsNullFunction.java 449149 2006-09-23 03:58:05Z crossley $
28: */
29: public class IsNullFunction extends AbstractExpression {
30:
31: public Object evaluate(ExpressionContext context)
32: throws ExpressionException {
33: Object result = null;
34: try {
35: result = ((Expression) arguments.get(0)).evaluate(context);
36: } catch (ExpressionException e) {
37: // FIXME: Hack to handle null variables
38: if (!e.getMessage().startsWith("Unknown variable")) {
39: throw e;
40: }
41: }
42: return result == null ? Boolean.TRUE : Boolean.FALSE;
43: }
44:
45: public void check() throws ExpressionException {
46: if (arguments.size() != 1) {
47: throw new ExpressionException(getDescription()
48: + " requires one argument.", getLine(), getColumn());
49: }
50: }
51:
52: public Class getResultType() {
53: return Boolean.class;
54: }
55:
56: public String getDescription() {
57: return "IsNull function";
58: }
59: }
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