在Ant中应用逻辑判断 Condition .【转】

? 好久不写ant脚本了，最近两天在用ant做web应用的安装部署脚本，为了实现web服务器的多版本兼容，必然要使用逻辑判断，比如我要判断是安装在weblogic8上还是weblogic9上，而在ant中处理逻辑判断真是麻烦，只能作用于task，要利用property来做判断，使用available来设置property。例如：

<?xml version="1.0" encoding="GB2312"?>
<project name="weblogic ant task" default="build">
?<target name="detect.file"?? >??
??<condition property="fileIsExists"?? >??
??<and>??
???<available file="c:/123.txt"/>
??</and>??
??</condition>
?</target>
?<target name="echoDemo" if="fileIsExists" depends="detect.file">??
??<echo message="hello ant"/>
?</target>
?<target name="build">??
??<antcall target="echoDemo"/>
?</target>
</project>
上面判断一个文件，如果存在的话 fileIsExists 就为true，echoDemo这个task在执行前会先判断fileIsExists 是否为true如果不为true就不执行了。c盘下面有123.txt的话会打印hello ant 否则不会打印。

这里面还有一个小陷阱，我习惯使用antcall，不喜欢使用depends，但是使用antcall的话就会有问题，例如我最开始这么写的，就不行。

<?xml version="1.0" encoding="GB2312"?>
<project name="weblogic ant task" default="build">
?<target name="detect.file">??
??<condition property="fileIsExists">??
??<and>??
???<available file="c:/123.txt"/>
??</and>??
??</condition>
?</target>
?<target name="echoDemo" if="fileIsExists">??
??<echo message="hello ant"/>
?</target>
?<target name="build">??
??<antcall target="detect.file"/>
??<antcall target="echoDemo"/>
?</target>
</project>

使用antcall的话在echoDemo这个task执行的时候fileIsExists这个属性永远不为true，即便在执行完detect.file后它已经为true了，但是它不会被传递到下一个task，没用深入研究过ant，所以具体内部实现还不了解。

下面是ant的官方参考文档

更复杂的可以参考

http://ant.apache.org/manual/CoreTasks/conditions.html

Condition

Description

Sets a property if a certain condition holds true - this is a generalization of Available and Uptodate.

If the condition holds true, the property value is set to true by default; otherwise, the property is not set. You can set the value to something other than the default by specifying the value attribute.

Conditions are specified as nested elements, you must specify exactly one condition.

Parameters

?

?

Parameters specified as nested elements

All conditions to test are specified as nested elements, for a complete list see here.

Examples

 <condition property="javamail.complete"> <and> <available classname="javax.activation.DataHandler"/> <available classname="javax.mail.Transport"/> </and> </condition>

sets the property javamail.complete if both the JavaBeans Activation Framework and JavaMail are available in the classpath.

 <condition property="isMacOsButNotMacOsX"> <and> <os family="mac"/> <not> <os family="unix"/> </not> </and> </condition>

sets the property isMacOsButNotMacOsX if the current operating system is MacOS, but not MacOS X - which Ant considers to be in the Unix family as well.

 <condition property="isSunOSonSparc"> <os name="SunOS" arch="sparc"/> </condition>

sets the property isSunOSonSparc if the current operating system is SunOS and if it is running on a sparc architecture.