Sets a property if a resource is available at runtime. This resource can be a file resource, a class in classpath or a JVM system resource.
If the resource is present, the property value is set to true by default, otherwise the property is not set. You can set the value to something specific by using the value attribute.
Normally, this task is used to set properties that are useful to avoid target execution depending on system parameters.
| Attribute | Description | Required |
| property | the name of the property to set. | Yes |
| value | the value to set the property to. Defaults to "true". | No |
| classname | the class to look for in classpath. | Yes |
| resource | the resource to look for in the JVM | |
| file | the file to look for. | |
| classpath | the classpath to
use when looking up classname. | No |
| classpathref | the classpath to use, given as reference to a path defined elsewhere. | No |
Available's classpath attribute is a path-like structure and can also be set via a nested
classpath element.
<available classname="org.whatever.Myclass" property="Myclass.present"/>
sets the property Myclass.present to the value "true"
if the class org.whatever.Myclass is found in Ant's classpath.
<property name="jaxp.jar" value="./lib/jaxp11/jaxp.jar"/>
<available file="${jaxp.jar}" property="jaxp.jar.present"/>
sets the property jaxp.jar.present to the value "true"
if the file ./lib/jaxp11/jaxp.jar is found.
...in project ...
<property name="jaxp.jar" value="./lib/jaxp11/jaxp.jar"/>
<path id="jaxp" location="${jaxp.jar}"/>
...in target ...
<available classname="javax.xml.transform.Transformer" classpathref="jaxp" property="jaxp11.present"/>
sets the property jaxp11.present to the value "true"
if the class javax.xml.transform.Transformer is found in the classpath referenced by jaxp (in this case, it is ./lib/jaxp11/jaxp.jar).
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