这应该工作：

 ＆LT;可用
      财产=hibernatetoolok
      类名=org.hibernate.tool.ant.HibernateToolTask​​
      classpathref =hibernatetool类路径/＆GT;＆lt;目标名称=hibernatetool如果=hibernatetoolok＆GT;
  ＆LT;的taskdef
    NAME =hibernatetool
    类名=org.hibernate.tool.ant.HibernateToolTask​​
    classpathref =hibernatetool类路径/＆GT;
＆LT; /目标与GT;
 

然后，你在哪里使用hibernatetool任务一定要添加任何目标取决于=hibernatetool。

Is there a way to check the classpath for a jar before executing a taskdef.

For example, I want to surround the following with a condition that checks if a jar that can has the class org.hibernate.tool.ant.HibernateToolTask before executing the taskdef

<taskdef name="hibernatetool" classname="org.hibernate.tool.ant.HibernateToolTask"  classpathref="hibernatetool-classpath" />

This should work:

<available 
      property="hibernatetoolok" 
      classname="org.hibernate.tool.ant.HibernateToolTask" 
      classpathref="hibernatetool-classpath" />

<target name="hibernatetool" if="hibernatetoolok">
  <taskdef 
    name="hibernatetool" 
    classname="org.hibernate.tool.ant.HibernateToolTask"  
    classpathref="hibernatetool-classpath" />
</target>

Then on any target where you use the hibernatetool task be sure to add depends="hibernatetool".