## Antlib

### Description

An antlib file is an xml file with a root element of "antlib". Antlib's elements are Apache Ant definition tasks - like and Taskdef, or any Ant task that extends `org.apache.tools.ant.taskdefs.AntlibDefinition`.

The current set of declarations bundled with Ant that do this are:

1. Typedef
2. Taskdef
3. Macrodef
4. Presetdef
5. Scriptdef

A group of tasks and types may be defined together in an antlib file. For example the file sample.xml contains the following:

>     <?xml version="1.0"?>
>     <antlib>
>        <typedef name="if" classname="org.acme.ant.If"/>
>        <typedef name="scriptpathmapper"
>                 classname="org.acme.ant.ScriptPathMapper"
>                 onerror="ignore"/>
>        <macrodef name="print">
>           <attribute name="file"/>
>           <sequential>
>              <concat taskname="print">
>                 <fileset dir="." includes="@{file}"/>
>              </concat>
>           </sequential>
>        </macrodef>
>     </antlib>

It defines two types or tasks, if and scriptpathmapper. This antlib file may be used in a build script as follows:

>     <typedef file="sample.xml"/>

The other attributes of `<typedef>` may be used as well. For example, assuming that the sample.xml is in a jar file sample.jar also containing the classes, the following build fragment will define the if and scriptpathmapper tasks/types and place them in the namespace uri samples:/acme.org.

>     <typedef resource="org/acme/ant/sample.xml"
>              uri="samples:/acme.org"/>

The definitions may then be used as follows:

>     <sample:if valuetrue="${props}" xmlns:sample="samples:/acme.org">
>        <sample:scriptpathmapper language="beanshell">
>           some bean shell
>        </sample:scriptpathmapper>
>     </sample:if>

### Antlib namespace

The name space URIs with the pattern antlib:java package are given special treatment.

When Ant encounters a element with a namespace URI with this pattern, it will check to see if there is a resource of the name antlib.xml in the package directory in the default classpath.

For example, assuming that the file antcontrib.jar has been placed in the directory ${ant.home}/lib and it contains the resource net/sf/antcontrib/antlib.xml which has all antcontrib's definitions defined, the following build file will automatically load the antcontrib definitions at location HERE:

>     <project default="deletetest" xmlns:antcontrib="antlib:net.sf.antcontrib">
>        <macrodef name="showdir">
>           <attribute name="dir"/>
>           <sequential>
>              <antcontrib:shellscript shell="bash">  <!-- HERE -->
>                 ls -Rl @{dir}
>              </antcontrib:shellscript>
>           </sequential>
>        </macrodef>

>        <target name="deletetest">
>           <delete dir="a" quiet="yes"/>
>           <mkdir dir="a/b"/>
>           <touch file="a/a.txt"/>
>           <touch file="a/b/b.txt"/>
>           <delete>
>              <fileset dir="a"/>
>           </delete>
>           <showdir dir="a"/>
>        </target>
>     </project>

The requirement that the resource is in the default classpath may be removed in future versions of Ant.

### Load antlib from inside of the buildfile

If you want to seperate the antlib from your local Ant installation, e.g. because you want to hold that jar in your projects SCM system, you have to specify a classpath, so that Ant could find that jar. The best solution is loading the antlib with `<taskdef>`.

>     <project xmlns:antcontrib="antlib:net.sf.antcontrib">
>        <taskdef uri="antlib:net.sf.antcontrib"
>                 resource="net/sf/antcontrib/antlib.xml"
>                 classpath="path/to/ant-contrib.jar"/>

>        <target name="iterate">
>           <antcontrib:for param="file">
>              <fileset dir="."/>
>              <sequential>
>                 <echo message="- @{file}"/>
>              </sequential>
>           </antcontrib:for>
>        </target>
>     </project>

### Current namespace

Definitions defined in antlibs may be used in antlibs. However the namespace that definitions are placed in are dependent on the `<typedef>` that uses the antlib. To deal with this problem, the definitions are placed in the namepace URI ant:current for the duration of the antlib execution. For example the following antlib defines the task `<if>`, the type `<isallowed>` and a macro `<ifallowed>` that makes use of the task and type:

>     <antlib xmlns:current="ant:current">
>        <taskdef name="if" classname="org.acme.ant.If"/>
>        <typedef name="isallowed" classname="org.acme.ant.Isallowed"/>
>        <macrodef name="ifallowed">
>           <attribute name="action"/>
>           <element name="do"/>
>           <sequential>
>              <current:if>
>                 <current:isallowed test="@{action}"/>
>                 <current:then>
>                    <do/>
>                 </current:then>
>              </current:if>
>           </sequential>
>        </macrodef>
>     </antlib>

### Other examples and comments

Antlibs may make use of other antlibs.

As the names defined in the antlib are in the namespace uri as specified by the calling `<typedef>` or by automatic element resolution, one may reuse names from core ant types and tasks, provided the caller uses a namespace uri. For example, the following antlib may be used to define defaults for various tasks:

>     <antlib xmlns:antcontrib="antlib:net.sf.antcontrib">
>        <presetdef name="javac">
>           <javac deprecation="${deprecation}"
>                  debug="${debug}"/>
>        </presetdef>
>        <presetdef name="delete">
>           <delete quiet="yes"/>
>        </presetdef>
>        <presetdef name="shellscript">
>           <antcontrib:shellscript shell="bash"/>
>        </presetdef>
>     </antlib>

This may be used as follows:

>     <project xmlns:local="localpresets">
>        <typedef file="localpresets.xml" uri="localpresets"/>
>        <local:shellscript>
>           echo "hello world"
>        </local:shellscript>
>     </project>