Apache 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.)
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. A relative path is resolved relative to the directory containing the buildfile. | No; defaults to the parent directory of the buildfile, unless overridden by the project's basedir or
the basedir property |
Optionally, a description for the project can be provided as a top-level <description> element
(see the 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.
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.
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, but it is also very easy to write your own.
All tasks can have a 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").
Note 1: 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.
Note 2: 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 are an important way to customize a build process or to just provide shortcuts for strings that are used repeatedly inside a buildfile.
In its most simple form properties are defined in the buildfile
(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: ${builddir}/classes. This
is resolved at run-time as build/classes.
Since Ant 1.8.0, property expansion has become much more powerful than simple key value pairs, more details can be found in the concepts section of this manual.
<project name="MyProject" default="dist" basedir=".">
<description>
simple example build file
</description>
<!-- set global properties for this build -->
<property name="src" location="src"/>
<property name="build" location="build"/>
<property name="dist" location="dist"/>
<target name="init">
<!-- Create the time stamp -->
<tstamp/>
<!-- Create the build directory structure used by compile -->
<mkdir dir="${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. Since 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.
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.
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.
Since Ant 1.8.2 the location attribute can also contain a wildcard in its last path component
(i.e. it can end in a *
) in order to support wildcard CLASSPATHs introduced with Java 6. Ant will
not expand or evaluate the wildcards and the resulting path may not work as anything else but
a CLASSPATH—or even as a CLASSPATH for JVM prior to Java 6.
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 ${build.dir}, except those that have the text Test in
their name, and the files specified in the referenced FileList.
If you want to use the same path-like structure for several tasks, you can define them with
a <path> element at the same level as <target>s, and reference them via their
id attribute—see References for an
example.
By default a path-like structure will re-evaluate all nested resource collections whenever it is used, which may lead
to unnecessary re-scanning of the filesystem. Since Ant 1.8.0, path has an optional cache
attribute, if it is set to true
, the path instance will only scan its nested resource collections once and assume
it doesn't change during the build anymore (the default for cache still is false
). Even if you are
using the path only in a single task it may improve overall performance to set cache to true
if you
are using complex nested constructs.
A path-like structure can include a reference to another path-like structure (a path being itself a resource
collection) via nested <path> elements:
<path id="base.path">
<pathelement path="${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}"/>
Since Ant 1.6, there is a shortcut for converting paths to OS specific strings in properties. One can use the expression ${toString:pathreference} to convert a path element reference to a string that can be used for a path argument. For example:
<path id="lib.path.ref">
<fileset dir="lib" includes="*.jar"/>
</path>
<javac srcdir="src" destdir="classes">
<compilerarg value="-Xbootclasspath/p:${toString:lib.path.ref}"/>
</javac>
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.
<arg value="-l -a"/>
is a single command-line argument containing a space character, not separate options -l
and -a
.
<arg line="-l -a"/>
This is a command line with two separate options, -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.
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.
Ant supports a plugin mechanism for using third party tasks. For using them you have to do two steps:
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:
${user.home}/.ant/lib${ant.home}/libFor the declaration there are several ways:
<taskdef name="taskname"
classname="ImplementationClass"/><taskdef name="for" classname="net.sf.antcontrib.logic.For"/> <for
... />
<taskdef><taskdef resource="net/sf/antcontrib/antcontrib.properties"/> <for
... />
<taskdef><taskdef resource="net/sf/antcontrib/antlib.xml"/> <for ... />
antlib: protocol handler<project xmlns:ac="antlib:net.sf.antcontrib"/> <ac:for ... />