尼斯和清洁解决方案如下：
是蚂蚁contribs.jar

Nice and clean solution below: Using ant-contribs.jar

在使用此解决方案，务必把下面一行顶部

When using this solution, be sure to put the following line on top

<!-- For <if> statements -->
<taskdef resource="net/sf/antcontrib/antlib.xml" />