Check multiple properties are set and not blank (ant) - ant

Question

I'm in a situation that involves running an ant build with optional parameters that are always specified but but not always defined, like so
ant -DBUILD_ENVIRONMENT=test -Dusername_ext= -Dconf.dir_ext= -Dcgi-dir_ext=
If the parameters are not given values on the command line they will be by loading a .properties file. I have the following code that will check if the property isset and is not blank.
<if>
<bool>
<and>
<isset property="username_ext"/>
<not>
<equals arg1="${username_ext}" arg2="" />
</not>
</and>
</bool>
<then>
<property name="username" value="${username_ext}" />
</then>
</if>
<property file="${BUILD_ENVIRONMENT}.properties" />
Since there are multiple properties it seems like I should write a target that will do the same actions for each property rather than repeat that code every time.
<antcall target="checkexists">
<property name="propname" value="username"/>
<property name="paramname" value="username_ext"/>
</antcall>
<antcall target="checkexists">
<property name="propname" value="conf.dir"/>
<property name="paramname" value="conf.dir_ext"/>
</antcall>
But AFAIK an antcall will not set a global property. How then can I write a target that will accept the name of a parameter it needs to check is set and is not blank, and then copy that in to a parameter that other targets can use?

Answer 1

Rather than using a target you could use a macro to conditionally set properties based on whether or not another property is set to a non-empty value.
<macrodef name="set-property">
<attribute name="name" />
<attribute name="if-property-isset" />
<attribute name="value" default="${#{if-property-isset}}" />
<sequential>
<condition property="#{name}" value="#{value}">
<and>
<isset property="#{if-property-isset}" />
<not>
<equals arg1="${#{if-property-isset}}" arg2="" />
</not>
</and>
</condition>
</sequential>
</macrodef>
<target name="test-macro">
<set-property name="username" if-property-isset="username_ext" />
<set-property name="conf.dir" if-property-isset="conf.dir_ext" />
<property name="conf.dir" value="default conf directory" />
<echo message="username = ${username}" />
<echo message="conf.dir = ${conf.dir}" />
</target>
Output
$ ant test-macro -Dusername_ext=jsmith -Dconf.dir_ext=
Buildfile: /your/project/build.xml
test-macro:
[echo] username = jsmith
[echo] conf.dir = default conf directory
BUILD SUCCESSFUL
Total time: 1 second
Alternate Property Value
This macro also allows you set the property to a different value than the one provided on the command line.
<target name="test-macro">
<set-property name="username" if-property-isset="username_ext"
value="It worked!" />
<set-property name="conf.dir" if-property-isset="conf.dir_ext" />
<property name="conf.dir" value="default conf directory" />
<echo message="username = ${username}" />
<echo message="conf.dir = ${conf.dir}" />
</target>
Output
$ ant test-macro -Dusername_ext=jsmith -Dconf.dir_ext=
Buildfile: /your/project/build.xml
test-macro:
[echo] username = It worked!
[echo] conf.dir = default conf directory
BUILD SUCCESSFUL
Total time: 1 second