Writing a Simple Buildfile

Using Ant

Writing a Simple Buildfile

Ant's buildfiles are written in XML. Each buildfile contains one project
and at least one (default) target. Targets contain task elements.
Each task element of the buildfile can have an id attribute and
can later be referred to by the value supplied to this. The value has
to be unique. (For additional information, see the
Tasks section below.)

Projects

A project has three attributes:

Attribute	Description	Required
name	the name of the project.	No
default	the default target to use when no target is supplied.	No; however, since Ant 1.6.0, every project includes an implicit target that contains any and all top-level tasks and/or types. This target will always be executed as part of the project's initialization, even when Ant is run with the -projecthelp option.
basedir	the base directory from which all path calculations are done. This attribute might be overridden by setting the "basedir" property beforehand. When this is done, it must be omitted in the project tag. If neither the attribute nor the property have been set, the parent directory of the buildfile will be used.	No

Optionally, a description for the project can be provided as a
top-level <description> element (see the href="CoreTypes/description.html">description type).

Each project defines one or more targets.
A target is a set of tasks you want
to be executed. When starting Ant, you can select which target(s) you
want to have executed. When no target is given,
the project's default is used.

Targets

A target can depend on other targets. You might have a target for compiling,
for example, and a target for creating a distributable. You can only build a
distributable when you have compiled first, so the distribute target
depends on the compile target. Ant resolves these dependencies.

It should be noted, however, that Ant's depends attribute
only specifies the order in which targets should be executed - it
does not affect whether the target that specifies the dependency(s) gets
executed if the dependent target(s) did not (need to) run.

More information can be found in the
dedicated manual page.

Tasks

A task is a piece of code that can be executed.

A task can have multiple attributes (or arguments, if you prefer). The value
of an attribute might contain references to a property. These references will be
resolved before the task is executed.

Tasks have a common structure:

<name attribute1="value1" attribute2="value2" ... />

where name is the name of the task,
attributeN is the attribute name, and
valueN is the value for this attribute.

There is a set of built-in tasks, along with a
number of
optional tasks, but it is also very
easy to write your own.

All tasks share a task name attribute. The value of
this attribute will be used in the logging messages generated by
Ant.

Tasks can be assigned an id attribute:

<taskname id="taskID" ... />

where taskname is the name of the task, and taskID is
a unique identifier for this task.
You can refer to the
corresponding task object in scripts or other tasks via this name.
For example, in scripts you could do:

 

<script ... >

  task1.setFoo("bar");

</script>

to set the foo attribute of this particular task instance.
In another task (written in Java), you can access the instance via
project.getReference("task1").

Note¹: If "task1" has not been run yet, then
it has not been configured (ie., no attributes have been set), and if it is
going to be configured later, anything you've done to the instance may
be overwritten.

Note²: Future versions of Ant will most likely not
be backward-compatible with this behaviour, since there will likely be no
task instances at all, only proxies.

Properties

Properties are an important way to customize a build process or
to just provide shortcuts for strings that are used repeatedly
inside a build file.

In its most simple form properties are defined in the build file
(for example by the property
task) or might be set outside Ant. A property has a name and a
value; the name is case-sensitive. Properties may be used in the
value of task attributes or in the nested text of tasks that support
them. This is done by placing the property name between
"${" and "}" in the
attribute value. For example, if there is a "builddir"
property with the value "build", then this could be used
in an attribute like this: ${builddir}/classes. This
is resolved at run-time as build/classes.

With Ant 1.8.0 property expansion has become much more powerful
than simple key value pairs, more details can be
found in the concepts section of this
manual.

Example Buildfile

 

<project name="MyProject" default="dist" basedir=".">

    <description>

        simple example build file

    </description>

  <!-- set global properties for this build -->

  <property name="src" location="src"/>

  <property name="build" location="build"/>

  <property name="dist"  location="dist"/>

 

  <target name="init">

    <!-- Create the time stamp -->

    <tstamp/>

    <!-- Create the build directory structure used by compile -->

    <mkdir dir="${build}"/>

  </target>

 

  <target name="compile" depends="init"

        description="compile the source " >

    <!-- Compile the java code from ${src} into ${build} -->

    <javac srcdir="${src}" destdir="${build}"/>

  </target>

 

  <target name="dist" depends="compile"

        description="generate the distribution" >

    <!-- Create the distribution directory -->

    <mkdir dir="${dist}/lib"/>

 

    <!-- Put everything in ${build} into the MyProject-${DSTAMP}.jar file -->

    <jar jarfile="${dist}/lib/MyProject-${DSTAMP}.jar" basedir="${build}"/>

  </target>

 

  <target name="clean"

        description="clean up" >

    <!-- Delete the ${build} and ${dist} directory trees -->

    <delete dir="${build}"/>

    <delete dir="${dist}"/>

  </target>

</project>

Notice that we are declaring properties outside any target. As of
Ant 1.6 all tasks can be declared outside targets (earlier version
only allowed <property>,<typedef> and
<taskdef>). When you do this they are evaluated before
any targets are executed. Some tasks will generate build failures if
they are used outside of targets as they may cause infinite loops
otherwise (<antcall> for example).

We have given some targets descriptions; this causes the projecthelp
invocation option to list them as public targets with the descriptions; the
other target is internal and not listed.

Finally, for this target to work the source in the src subdirectory
should be stored in a directory tree which matches the package names. Check the
<javac> task for details.

Token Filters

A project can have a set of tokens that might be automatically expanded if
found when a file is copied, when the filtering-copy behavior is selected in the
tasks that support this. These might be set in the buildfile
by the filter task.

Since this can potentially be a very harmful behavior,
the tokens in the files must
be of the form @token@, where
token is the token name that is set
in the <filter> task. This token syntax matches the syntax of other build systems
that perform such filtering and remains sufficiently orthogonal to most
programming and scripting languages, as well as with documentation systems.

Note: If a token with the format @token@
is found in a file, but no
filter is associated with that token, no changes take place;
therefore, no escaping
method is available - but as long as you choose appropriate names for your
tokens, this should not cause problems.

Warning: If you copy binary files with filtering turned on, you can corrupt the
files. This feature should be used with text files only.

Path-like Structures

You can specify PATH- and CLASSPATH-type
references using both
":" and ";" as separator
characters. Ant will
convert the separator to the correct character of the current operating
system.

Wherever path-like values need to be specified, a nested element can
be used. This takes the general form of:

 

    <classpath>

      <pathelement path="${classpath}"/>

      <pathelement location="lib/helper.jar"/>

    </classpath>

The location attribute specifies a single file or
directory relative to the project's base directory (or an absolute
filename), while the path attribute accepts colon-
or semicolon-separated lists of locations. The path
attribute is intended to be used with predefined paths - in any other
case, multiple elements with location attributes should be
preferred.

As a shortcut, the <classpath> tag
supports path and
location attributes of its own, so:

 

    <classpath>

      <pathelement path="${classpath}"/>

    </classpath>

can be abbreviated to:

 

    <classpath path="${classpath}"/>

In addition, one or more
Resource Collections
can be specified as nested elements (these must consist of
file-type resources only).
Additionally, it should be noted that although resource collections are
processed in the order encountered, certain resource collection types
such as fileset,
dirset and
files
are undefined in terms of order.

 

    <classpath>

      <pathelement path="${classpath}"/>

      <fileset dir="lib">

        <include name="**/*.jar"/>

      </fileset>

      <pathelement location="classes"/>

      <dirset dir="${build.dir}">

        <include name="apps/**/classes"/>

        <exclude name="apps/**/*Test*"/>

      </dirset>

      <filelist refid="third-party_jars"/>

    </classpath>

This builds a path that holds the value of ${classpath},
followed by all jar files in the lib directory,
the classes directory, all directories named
classes under the apps subdirectory of
${build.dir}, except those
that have the text Test in their name, and
the files specified in the referenced FileList.

If you want to use the same path-like structure for several tasks,
you can define them with a <path> element at the
same level as targets, and reference them via their
id attribute--see References for an
example.

By default a path like structure will re-evaluate all nested
resource collections whenever it is used, which may lead to
unnecessary re-scanning of the filesystem. Since Ant 1.8.0 path has
an optional cache attribute, if it is set to true, the path
instance will only scan its nested resource collections once and
assume it doesn't change during the build anymore (the default
for cache still is false). Even if you are using the
path only in a single task it may improve overall performance to set
cache to true if you are using complex nested
constructs.

A path-like structure can include a reference to another path-like
structure (a path being itself a resource collection)
via nested <path> elements:

 

    <path id="base.path">

      <pathelement path="${classpath}"/>

      <fileset dir="lib">

        <include name="**/*.jar"/>

      </fileset>

      <pathelement location="classes"/>

    </path>

 

    <path id="tests.path" cache="true">

      <path refid="base.path"/>

      <pathelement location="testclasses"/>

    </path>

The shortcuts previously mentioned for <classpath> are also valid for <path>.For example:

 

    <path id="base.path">

      <pathelement path="${classpath}"/>

    </path>

can be written as:

 

    <path id="base.path" path="${classpath}"/>

Path Shortcut

In Ant 1.6 a shortcut for converting paths to OS specific strings
in properties has been added. One can use the expression
${toString:pathreference} to convert a path element
reference to a string that can be used for a path argument.
For example:

 

  <path id="lib.path.ref">

    <fileset dir="lib" includes="*.jar"/>

  </path>

  <javac srcdir="src" destdir="classes">

    <compilerarg arg="-Xbootclasspath/p:${toString:lib.path.ref}"/>

  </javac>

Command-line Arguments

Several tasks take arguments that will be passed to another
process on the command line. To make it easier to specify arguments
that contain space characters, nested arg elements can be used.

Attribute	Description	Required
value	a single command-line argument; can contain space characters.	Exactly one of these.
file	The name of a file as a single command-line argument; will be replaced with the absolute filename of the file.
path	A string that will be treated as a path-like string as a single command-line argument; you can use ; or : as path separators and Ant will convert it to the platform's local conventions.
pathref	Reference to a path defined elsewhere. Ant will convert it to the platform's local conventions.
line	a space-delimited list of command-line arguments.
prefix	A fixed string to be placed in front of the argument. In the case of a line broken into parts, it will be placed in front of every part. Since Ant 1.8.	No
suffix	A fixed string to be placed immediately after the argument. In the case of a line broken into parts, it will be placed after every part. Since Ant 1.8.	No

It is highly recommended to avoid the line version
when possible. Ant will try to split the command line in a way
similar to what a (Unix) shell would do, but may create something that
is very different from what you expect under some circumstances.

Examples

 

  <arg value="-l -a"/>

is a single command-line argument containing a space character,
not separate commands "-l" and "-a".

 

  <arg line="-l -a"/>

This is a command line with two separate arguments, "-l" and "-a".

 

  <arg path="/dir;/dir2:\dir3"/>

is a single command-line argument with the value
\dir;\dir2;\dir3 on DOS-based systems and
/dir:/dir2:/dir3 on Unix-like systems.

References

Any project element can be assigned an identifier using its
id attribute. In most cases the element can subsequently
be referenced by specifying the refid attribute on an
element of the same type. This can be useful if you are going to
replicate the same snippet of XML over and over again--using a
<classpath> structure more than once, for example.

The following example:

 

<project ... >

  <target ... >

    <rmic ...>

      <classpath>

        <pathelement location="lib/"/>

        <pathelement path="${java.class.path}/"/>

        <pathelement path="${additional.path}"/>

      </classpath>

    </rmic>

  </target>

 

  <target ... >

    <javac ...>

      <classpath>

        <pathelement location="lib/"/>

        <pathelement path="${java.class.path}/"/>

        <pathelement path="${additional.path}"/>

      </classpath>

    </javac>

  </target>

</project>

could be rewritten as:

 

<project ... >

  <path id="project.class.path">

    <pathelement location="lib/"/>

    <pathelement path="${java.class.path}/"/>

    <pathelement path="${additional.path}"/>

  </path>

 

  <target ... >

    <rmic ...>

      <classpath refid="project.class.path"/>

    </rmic>

  </target>

 

  <target ... >

    <javac ...>

      <classpath refid="project.class.path"/>

    </javac>

  </target>

</project>

All tasks that use nested elements for
PatternSets,
FileSets,
ZipFileSets or
path-like structures accept references to these structures
as shown in the examples. Using refid on a task will ordinarily
have the same effect (referencing a task already declared), but the user
should be aware that the interpretation of this attribute is dependent on the
implementation of the element upon which it is specified. Some tasks (the
property task is a handy example)
deliberately assign a different meaning to refid.

Use of external tasks

Ant supports a plugin mechanism for using third party tasks. For using them you
have to do two steps:

1. place their implementation somewhere where Ant can find them


2. declare them.

Don't add anything to the CLASSPATH environment variable - this is often the
reason for very obscure errors. Use Ant's own mechanisms
for adding libraries:

• via command line argument -lib


• adding to ${user.home}/.ant/lib


• adding to ${ant.home}/lib

For the declaration there are several ways:

• declare a single task per using instruction using
  <taskdef name="taskname"
classname="ImplementationClass"/>


<taskdef name="for" classname="net.sf.antcontrib.logic.For" />
<for ... />
  


• declare a bundle of tasks using a properties-file holding these
  taskname-ImplementationClass-pairs and <taskdef>


<taskdef resource="net/sf/antcontrib/antcontrib.properties" />
<for ... />
  


• declare a bundle of tasks using a xml-file holding these
  taskname-ImplementationClass-pairs and <taskdef>


<taskdef resource="net/sf/antcontrib/antlib.xml" />
<for ... />
  


• declare a bundle of tasks using a xml-file named antlib.xml, XML-namespace and
  antlib: protocoll handler
  
  
  <project xmlns:ac="antlib:net.sf.antconrib"/>
<ac:for ... />
  

If you need a special function, you should

1. have a look at this manual, because Ant provides lot of tasks


2. have a look at the external task page in the manual
   (or better online)


3. have a look at the external task wiki
   page


4. ask on the Ant user list


5. implement (and share) your own