How to check if a property has value in Ant - ant

Question

I have an Ant XML file which I use for build.
I have 3 properties. I want to break the build if these properties does not contain any value. Also I want to break the build if the value is empty.
How can I do this in Ant?
I a using Ant and not Ant-contrib.

Answer 1

You can use conditions using the <fail> task:
<fail message="Property "foo" needs to be set to a value">
<condition>
<or>
<equals arg1="${foo}" arg2=""/>
<not>
<isset property="foo"/>
</not>
</or>
</condition>
This is equivalent to saying if (not set ${foo} or ${foo} = "") is pseudocode. You have to read the XML conditions from the inside out.
You could have used the <unless> clause on the <fail> task if you only cared whether or not the variable was set, and not whether it has an actual value.
<fail message="Property "foo" needs to be set"
unless="foo"/>
However, this won't fail if the property is set, but has no value.
There's a trick that can make this simpler
<!-- Won't change the value of `${foo}` if it's already defined -->
<property name="foo" value=""/>
<fail message="Property "foo" has no value">
<condition>
<equals arg1="${foo}" arg2=""/>
</condition>
</fail>
Remember that I can't reset a property! If ${foo} already has a value, the <property> task above won't do anything. This way, I can eliminate the <isset> condition. It might be nice since you have three properties:
<property name="foo" value=""/>
<property name="bar" value=""/>
<property name="fubar" value=""/>
<fail message="You broke the build, you dufus">
<condition>
<or>
<equals arg1="${foo}" arg2=""/>
<equals arg1="${bar}" arg2=""/>
<equals arg1="${fubar}" arg2=""/>
</or>
</condition>
</fail>

Answer 2

Building on the other answers, this is my preferred form, as a Macro:
<!-- Macro to require a property is not blank -->
<macrodef name="prop-require">
<attribute name="prop"/>
<sequential>
<fail message="Property "#{prop}" must be set">
<condition>
<not>
<isset property="#{prop}"/>
</not>
</condition>
</fail>
<fail message="Property "#{prop}" must not be empty">
<condition>
<equals arg1="${#{prop}}" arg2=""/>
</condition>
</fail>
</sequential>
</macrodef>
To Be used as:
<target name="deploy.war" description="Do the war deployment ;)">
<prop-require prop="target.vm" />
<prop-require prop="target.vip" />
<!-- ... -->
For brevity you can collapse the two fail elements into one by using an <or>, but I prefer my error messages to treat me like I cannot think for myself ;)

Answer 3

You could try using conditions... or creating a target with unless

Answer 4

With Ant addon Flaka you may use patterns like :
<property name="foo" value="bar"/>
...
<fl:unless test="has.property.foo">
...
</fl:unless>
...
<fl:when test="has.property.foo">
...
</fl:when>
Concrete check for emptyness :
<fl:when test=" empty '${foo}' ">
<fail message="Houston we have a problem!!"/>
</fl:when>
A complete example, also using some equals check with 'eq' (opposite would be 'neq'):
<project xmlns:fl="antlib:it.haefelinger.flaka">
<!-- some if/then/else construct -->
<fl:choose>
<!-- if -->
<when test=" '${buildtype}' eq 'prod' ">
<!-- then -->
<echo>..starting ProductionBuild</echo>
</when>
<when test=" '${buildtype}' eq 'test' ">
<!-- then -->
<echo>..starting TestBuild</echo>
</when>
<!-- else -->
<otherwise>
<fl:unless test="has.property.dummybuild">
<fail message="No valid buildtype !, found => '${buildtype}'"/>
</fl:unless>
<echo>.. is DummyBuild</echo>
</otherwise>
</fl:choose>
</project>
output with ant -f build.xml -Dbuildtype=prod or
ant -f build.xml -Dbuildtype=prod -Ddummybuild=whatever
[echo] ..starting ProductionBuild
output with typo => ant - build.xml -Dbuildtype=testt
BUILD FAILED
/home/rosebud/workspace/AntTest/build.xml:21: No valid buildtype !, found => 'testt'
output with ant -f build.xml -Ddummybuild=whatever
[echo] .. is DummyBuild

Answer 5

I'm on an older version of Ant, so isset wasn't available. Instead I used the following notation with the double $ in the equals.
<target name="xxx">
<echo message="${contextRoot}" />
<if>
<!-- check if the contextRoot property is defined. -->
<equals arg1="${contextRoot}" arg2="$${contextRoot}" />
<then>
<!-- it isn't set, set a default -->
<property name="contextRoot" value="/WebAppCtx" />
</then>
</if>
<echo message="${contextRoot}" />
</target>

Answer 6

Try this.
<condition property="isPropertySet" value="true" else="false">
<and>
<isset property="my_property"/>
<length string="${my_property}" trim="true" when="greater" length="0"/>
</and>
</condition>
<fail unless="isPropertySet" message="The property my_property is not set."/>

Answer 7

Since Ant 1.9.1, it is possible to add if and unless attributes on all
tasks and nested elements using special namespaces.
In order to use this feature you need to add the following namespace declarations
xmlns:if="ant:if"
xmlns:unless="ant:unless"
The if and unless namespaces support the following conditions:
true - true if the value of the attribute evaluates to true
blank - true if the value of the attribute is null or empty
set - true if the specified property is set
Sample:
<project name="tryit"
xmlns:if="ant:if"
xmlns:unless="ant:unless">
<exec executable="java">
<arg line="-X" if:true="${showextendedparams}"/>
<arg line="-version" unless:true="${showextendedparams}"/>
</exec>
<condition property="onmac">
<os family="mac"/>
</condition>
<echo if:set="onmac">running on MacOS</echo>
<echo unless:set="onmac">not running on MacOS</echo>
</project>
From Ant manual "If And Unless"