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<div class="main">
<div class="content">
<h1 class="title">Frequently Asked Questions</h1>
<h3 class="section">Questions</h3>
<h4 class="toc">About this FAQ</h4>
<ul>
<li><a href="#latest-version">
Where do I find the latest version of this
document?
</a></li>
<li><a href="#adding-faqs">
How can I contribute to this FAQ?
</a></li>
<li><a href="#creating-faq">
How do you create the HTML version of this
FAQ?
</a></li>
</ul>
<h4 class="toc">General</h4>
<ul>
<li><a href="#what-is-ant">
What is Apache Ant?
</a></li>
<li><a href="#ant-name">
Why do you call it Ant?
</a></li>
<li><a href="#history">
Tell us a little bit about Ant's history.
</a></li>
</ul>
<h4 class="toc">Installation</h4>
<ul>
<li><a href="#java-version">
Which version of Java is required to run
Apache Ant?
</a></li>
<li><a href="#no-gnu-tar">
I get checksum errors when I try to extract the
<code>tar.gz</code> distribution file. Why?
</a></li>
<li><a href="#RedHat_ES_3">
How do you get ant-1.6.x (or any version later than
1.5.2) to work on on RedHat ES 3?
</a></li>
</ul>
<h4 class="toc">How do I ...</h4>
<ul>
<li><a href="#precompile-jsps">
How to I precompile Java Server Pages (JSPs)?
</a></li>
<li><a href="#implement-os-specific-configuration">
How do I realize os--specific configurations?
</a></li>
<li><a href="#adding-external-tasks">
How do I add an external task that I've written to the
page "External Tools and Tasks"?
</a></li>
<li><a href="#create-extensions">
How do I create new tasks?
</a></li>
<li><a href="#passing-cli-args">
How do I pass parameters from the command line to my
build file?
</a></li>
<li><a href="#jikes-switches">
How can I use Jikes-specific command-line
switches?
</a></li>
<li><a href="#shell-redirect-1">
How do I include a < character in my command-line arguments?
</a></li>
<li><a href="#shell-redirect-2">
How do I redirect standard input or standard output
in the <code><exec></code> task?
</a></li>
<li><a href="#batch-shell-execute">
How do I execute a batch file or shell script from Ant?
</a></li>
<li><a href="#multi-conditions">
I want to execute a particular target only if
multiple conditions are true.
</a></li>
<li><a href="#encoding">
How can I include national characters like German
umlauts in my build file?
</a></li>
<li><a href="#use-zip-instead-of-jar">
How do I use <code>jar</code>'s <code>M</code> switch?
I don't want a MANIFEST.
</a></li>
<li><a href="#propertyvalue-as-name-for-property">
How can I do something like <code><property name="prop"
value="${${anotherprop}}"/></code> (double expanding the property)?
</a></li>
<li><a href="#delete-directory-children-only">
How can I delete everything beneath a particular directory,
preserving the directory itself?
</a></li>
<li><a href="#delete-directory-only-if-empty">
How can I delete a particular directory,
if and only if it is empty?
</a></li>
</ul>
<h4 class="toc">It doesn't work (as expected)</h4>
<ul>
<li><a href="#general-advice">
General Advice
</a></li>
<li><a href="#always-recompiles">
Why does Ant always recompile all my Java files?
</a></li>
<li><a href="#defaultexcludes">
I've used a <code><delete></code> task to
delete unwanted SourceSafe control files (CVS files, editor
backup files, etc.), but it doesn't seem to work; the files
never get deleted. What's wrong?
</a></li>
<li><a href="#stop-dependency">
I have a target I want to skip if a property is set,
so I have <code>unless="property"</code> as an attribute
of the target, but all the targets this target
depends on are still executed. Why?
</a></li>
<li><a href="#include-order">
In my <code><fileset></code>, I've put in an
<code><exclude></code> of all files followed by an
<code><include></code> of just the files I want, but it
isn't giving me any files at all. What's wrong?
</a></li>
<li><a href="#properties-not-trimmed">
<code>ant</code> failed to build my program via javac
even when I put the needed jars in an external
<code>build.properties</code> file and reference them by
<code>pathelement</code> or <code>classpath refid</code>.
</a></li>
<li><a href="#winzip-lies">
Ant creates WAR files with a lower-case
<code>web-inf</code> or JAR files with a lower-case
<code>meta-inf</code> directory.
</a></li>
<li><a href="#NoClassDefFoundError">
I installed Ant 1.6.x and now get
<code>Exception in thread "main" java.lang.NoClassDefFoundError:
</code>
</a></li>
<li><a href="#InstantiationException">
I installed Ant 1.6.x and now get
<code>java.lang.InstantiationException: org.apache.tools.ant.Main</code>
</a></li>
<li><a href="#mangled-manifest">
Whenever I use the Ant jar or manifest related tasks, long lines in
my manifest are wrapped at 70 characters and the resulting jar does
not work in my application server. Why does Ant do this?
</a></li>
<li><a href="#CreateProcess_error_2">
<code><exec></code> fails with <code>"Cannot run
program "...":CreateProcess error=2"</code> on
Windows.
</a></li>
</ul>
<h4 class="toc">Apache Ant and IDEs/Editors</h4>
<ul>
<li><a href="#integration">
Is Apache Ant supported by my IDE/Editor?
</a></li>
<li><a href="#emacs-mode">
Why doesn't (X)Emacs/vi/MacOS X's project builder
correctly parse the error messages generated by Ant?
</a></li>
</ul>
<h4 class="toc">Advanced Issues</h4>
<ul>
<li><a href="#dtd">
Is there a DTD that I can use to validate my build
files?
</a></li>
<li><a href="#xml-entity-include">
How do I include an XML snippet in my build file?
</a></li>
<li><a href="#mail-logger">
How do I send an email with the result of my build
process?
</a></li>
<li><a href="#listener-properties">
How do I get at the properties that Ant was running
with from inside BuildListener?
</a></li>
</ul>
<h4 class="toc">Known Problems</h4>
<ul>
<li><a href="#input-makes-exec-hang">
<code><exec></code> causes other tasks to hang
or leads to strange behaviour of <code><input></code>
tasks.
</a></li>
<li><a href="#javac-stackoverflow">
<code><javac></code> causes a
StackOverflowError
</a></li>
<li><a href="#170-requires-junit">
Ant 1.7.0 doesn't build from sources without
JUnit
</a></li>
<li><a href="#remove-cr">
<chmod> or <exec> doesn't work in Ant
1.3 on Unix
</a></li>
<li><a href="#delegating-classloader">
<style> or <junit> ignores my
<classpath>
</a></li>
<li><a href="#delegating-classloader-1.5">
<style> or <junit> ignores my
<classpath> - Ant 1.5.x version
</a></li>
<li><a href="#delegating-classloader-1.6">
<style> or <junit> ignores my
<classpath> - Ant 1.6.x version
</a></li>
<li><a href="#unknownelement.taskcontainer">
Why do my custom task containers see Unknown Elements in Ant 1.6
- they worked in Ant 1.5?
</a></li>
<li><a href="#oom-on-mac">
Ant runs into an infinite loop/throws an OutOfMemoryError
when I compile my project under Mac OS X.
</a></li>
<li><a href="#extension-point-and-import">
<code>extension-point</code> doesn't work
with <code>import</code> like the documentation
states.
</a></li>
</ul>
<h3 class="section">Answers</h3>
<p class="faq">
<a name="latest-version"></a>
Where do I find the latest version of this
document?
</p>
<p>The latest version can always be found at Apache Ant's homepage
<a href="http://ant.apache.org/faq.html">http://ant.apache.org/faq.html</a>.</p>
<p class="faq">
<a name="adding-faqs"></a>
How can I contribute to this FAQ?
</p>
<p>The page you are looking it is generated from
<a href="http://svn.apache.org/repos/asf/ant/core/trunk/xdocs/faq.xml">this</a>
document. If you want to add a new question, please submit
a patch against this document to one of Ant's mailing lists;
hopefully, the structure is self-explanatory.</p>
<p>If you don't know how to create a patch, see the patches
section of <a href="http://jakarta.apache.org/site/source.html">this
page</a>.</p>
<p class="faq">
<a name="creating-faq"></a>
How do you create the HTML version of this
FAQ?
</p>
<p>We use
<a href="http://jakarta.apache.org/velocity/anakia.html">Anakia</a>
to render the HTML version from the original XML file.</p>
<p>The Velocity stylesheets used to process the XML files can
be found in the <code>xdocs/stylesheets</code> subdirectory of
Ant's SVN repository - the build file
<code>docs.xml</code> at the top level of the ant SVN
module (trunk) is used to drive Anakia.</p>
<p>To transform the xml into html, one needs velocity 1.4.
The command to run is :</p>
<p>
<code>ant -Dvelocity.dir=[installation path of velocity] -f docs.xml</code>
</p>
<p class="faq">
<a name="what-is-ant"></a>
What is Apache Ant?
</p>
<p> Ant is a Java-based build tool. In theory, it is kind of
like Make, without Make's wrinkles and with the full
portability of pure Java code.</p>
<p class="faq">
<a name="ant-name"></a>
Why do you call it Ant?
</p>
<p>According to Ant's original author, James Duncan
Davidson, the name is an acronym for "Another Neat
Tool".</p>
<p>Later explanations go along the lines of "ants
do an extremely good job at building things", or
"ants are very small and can carry a weight dozens of times
their own" - describing what Ant is intended to
be.</p>
<p class="faq">
<a name="history"></a>
Tell us a little bit about Ant's history.
</p>
<p>Initially, Ant was part of the Tomcat code base, when it was
donated to the Apache Software Foundation. It was
created by James Duncan Davidson, who is also the original
author of Tomcat. Ant was there to build Tomcat, nothing
else.</p>
<p>Soon thereafter, several open source Java projects realized
that Ant could solve the problems they had with Makefiles.
Starting with the projects hosted at Jakarta and the old Java
Apache project, Ant spread like a virus and is now the build
tool of choice for a lot of projects.</p>
<p>In January 2000, Ant was moved to a separate CVS module and
was promoted to a project of its own, independent of
Tomcat, and became Apache Ant.</p>
<p>The first version of Ant that was exposed to a larger audience
was the one that shipped with Tomcat's 3.1 release on 19 April
2000. This version has later been referred to as Ant
0.3.1.</p>
<p>The first official release of Ant as a stand-alone product was
Ant 1.1, released on 19 July 2000. The complete release
history:</p>
<table class="ForrestTable" cellspacing="1" cellpadding="4">
<tr>
<th colspan="1" rowspan="1"
valign="top" align="left">
Ant Version
</th>
<th colspan="1" rowspan="1"
valign="top" align="left">
Release Date
</th>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
19 July 2000
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.2
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
24 October 2000
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.3
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
3 March 2001
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.4
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
3 September 2001
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.4.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
11 October 2001
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.5
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
10 July 2002
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.5.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
3 October 2002
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.5.2
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
3 March 2003
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.5.3
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
9 April 2003
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.5.4
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
12 August 2003
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.0
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
18 December 2003
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
12 February 2004
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.2
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
16 July 2004
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.3
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
28 April 2005
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.4
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
19 May 2005
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.5
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
2 June 2005
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.7.0
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
19 December 2006
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.7.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
27 June 2008
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.8.0
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
8 February 2010
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.8.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
7 May 2010
</td>
</tr>
</table>
<p class="faq">
<a name="java-version"></a>
Which version of Java is required to run
Apache Ant?
</p>
<p>You will need Java installed on your system, version 1.4 or
later required, 1.5 or later strongly recommended. The later
the version of Java, the more Ant tasks you get.</p>
<p>If only the JRE is present but not a full JDK then many
tasks will not work.</p>
<p>The following table lists the minimum Java versions
required to compile and run Ant. Note that most committers
work with more recent versions of the JDK and that Ant doesn't
get tested much for older versions.</p>
<table class="ForrestTable" cellspacing="1" cellpadding="4">
<tr>
<th colspan="1" rowspan="1"
valign="top" align="left">
Ant Version
</th>
<th colspan="1" rowspan="1"
valign="top" align="left">
Minimum Java Version
</th>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.1 up to 1.5.4
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.1
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.6.0 up to 1.6.5
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.2
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.7.0 up to 1.7.1
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.3
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.8.0 up to current svn trunk
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
1.4
</td>
</tr>
</table>
<p class="faq">
<a name="no-gnu-tar"></a>
I get checksum errors when I try to extract the
<code>tar.gz</code> distribution file. Why?
</p>
<p>Ant's distribution contains file names that are longer
than 100 characters, which is not supported by the standard
tar file format. Several different implementations of tar use
different and incompatible ways to work around this
restriction.</p>
<p>Ant's <tar> task can create tar archives that use
the GNU tar extension, and this has been used when putting
together the distribution. If you are using a different
version of tar (for example, the one shipping with Solaris),
you cannot use it to extract the archive.</p>
<p>The solution is to either install GNU tar, which can be
found <a href="http://www.gnu.org/software/tar/tar.html">here</a>,
or use the zip archive instead (you can extract it using
<code>jar xf</code>).</p>
<p class="faq">
<a name="RedHat_ES_3"></a>
How do you get ant-1.6.x (or any version later than
1.5.2) to work on on RedHat ES 3?
</p>
<p>Redhat ES 3.0 comes installed with ant 1.5.2. Even if you
have your PATH and ANT_HOME variables set correctly to a later
version of ant, you will always be forced to use the
preinstalled version.</p>
<p>To use a later version of ant on this OS you could do the
following:</p>
<pre class="code">
$ ant -version
Apache Ant version 1.5.2-23 compiled on November 12 2003
$ su -
# rpm -e ant ant-libs
# exit
$ hash -r
$ ant -version
Apache Ant version 1.6.2 compiled on July 16 2004
</pre>
<p class="faq">
<a name="precompile-jsps"></a>
How to I precompile Java Server Pages (JSPs)?
</p>
<p>Apache Ant has a built in optional task <a href="/manual/Tasks/jspc.html"><jspc></a>
which was intended for that. <b>But this task is deprecated.</b>
Here the alternative suggested by the manual:</p>
<p><i>Instead of relying on container specific JSP-compilers we suggest deploying
the raw files (*.jsp) and use the container build-in functions: after deploying
run a test suite (e.g. with
<a href="http://jakarta.apache.org/cactus/">Cactus</a> or
<a href="http://httpunit.sourceforge.net/">HttpUnit</a>) against the deployed web
application. So you'll get then test result and the compiled JSPs.</i></p>
<p class="faq">
<a name="implement-os-specific-configuration"></a>
How do I realize os--specific configurations?
</p>
<p>The core idea is using property files which name accords to the
os-name. Then simply use the build-in property <tt>os.name</tt>.</p>
<p>For better use you should also provide a file with default values.
But be careful with the correct os-names. For test simply <echo>
the ${os.name} on all machines and you can be sure to use the right
file names.</p>
<pre class="code">
<property file="${os.name}.properties"/>
<property file="default.properties"/>
</pre>
<p class="faq">
<a name="adding-external-tasks"></a>
How do I add an external task that I've written to the
page "External Tools and Tasks"?
</p>
<p>Join and post a message to the dev or user mailing
list (one list is enough), including the following
information:</p>
<ul>
<li>the name of the task/tool</li>
<li>a short description of the task/tool</li>
<li>a Compatibility: entry stating with which version(s) of
Ant the tool/task is compatible to</li>
<li>a URL: entry linking to the main page of the tool/task</li>
<li>a Contact: entry containing the email address or the URL
of a webpage for the person or list to contact for issues
related to the tool/task. <strong>Note that we'll add a
link on the page, so any email address added there is not
obfuscated and can (and probably will) be abused by robots
harvesting websites for addresses to spam.</strong></li>
<li>a License: entry containing the type of license for the
tool/task</li>
</ul>
<p>The preferred format for this information is a patch to <a href="http://svn.apache.org/repos/asf/ant/core/trunk/xdocs/external.xml">this</a>
document.</p>
<p>If you have written something bigger than a 'simple plugin' to Ant it
may be better to add the link to <a href="projects.html">projects.html</a>.
The procedure to add it is the same. The file to patch is <a href="http://svn.apache.org/repos/asf/ant/core/trunk/xdocs/projects.xml">this</a>
document. The syntax of that file is the same.</p>
<p class="faq">
<a name="create-extensions"></a>
How do I create new tasks?
</p>
<p>Apart from a lot of information on using Ant, the
<a href="manual/index.html">Manual</a> also contains information
on how to extend Ant with new tasks. This information
can be found under "Developing with Ant".</p>
<p>Chances are that someone else already created the task you
want to create, it may be wise to see
<a href="external.html">External Tools and Tasks</a> and
<a href="projects.html">Related Projects</a> first.</p>
<p class="faq">
<a name="passing-cli-args"></a>
How do I pass parameters from the command line to my
build file?
</p>
<p>Use properties. Using <code>ant
-D<em>name</em>=<em>value</em></code> lets you define values for
properties on the Ant command line. These properties can then be
used within your build file as
any normal property: <code>${<em>name</em>}</code> will put in
<code><em>value</em></code>.</p>
<p class="faq">
<a name="jikes-switches"></a>
How can I use Jikes-specific command-line
switches?
</p>
<p>A couple of switches are supported via "magic"
properties:</p>
<table class="ForrestTable" cellspacing="1" cellpadding="4">
<tr>
<th colspan="1" rowspan="1"
valign="top" align="left">
switch
</th>
<th colspan="1" rowspan="1"
valign="top" align="left">
property
</th>
<th colspan="1" rowspan="1"
valign="top" align="left">
default
</th>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
+E
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
build.compiler.emacs
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
false == not set
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
+P
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
build.compiler.pedantic
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
false == not set
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
+F
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
build.compiler.fulldepend
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
false == not set
</td>
</tr>
<tr>
<td colspan="1" rowspan="1"
valign="top" align="left">
<strong>(Only for Ant < 1.4; replaced by the
<code><strong>nowarn</strong></code>
attribute of the <code><strong><javac></strong></code>
task after that.)</strong><br />-nowarn
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
build.compiler.warnings
</td>
<td colspan="1" rowspan="1"
valign="top" align="left">
true == not set
</td>
</tr>
</table>
<p>With Ant >= 1.5, you can also use nested
<code><compilerarg></code> elements with the
<code><javac></code> task.</p>
<p class="faq">
<a name="shell-redirect-1"></a>
How do I include a < character in my command-line arguments?
</p>
<p>The short answer is "Use: <code>&lt;</code>".</p>
<p>The long answer is that this probably won't do what you
want anyway (see <a href="#shell-redirect-2">the next
section</a>).</p>
<p class="faq">
<a name="shell-redirect-2"></a>
How do I redirect standard input or standard output
in the <code><exec></code> task?
</p>
<p>Say you want to redirect the standard output stream of the
<code>m4</code> command to write to a file, something
like:</p>
<pre class="code">
shell-prompt> m4 foo.m4 > foo
</pre>
<p>and try to translate it into</p>
<pre class="code">
<exec executable="m4">
<arg value="foo.m4"/>
<arg value="&gt;"/>
<arg value="foo"/>
</exec>
</pre>
<p>This will not do what you expect. The output redirection is
performed by your shell, not the command itself, so this
should read:</p>
<pre class="code">
<exec executable="/bin/sh">
<arg value="-c" />
<arg value="m4 foo.m4 &gt; foo" />
</exec>
</pre>
<p>Note that you must use the <code>value</code> attribute of
<code><arg></code> in the last element, in order to have
the command passed as a single, quoted argument. Alternatively,
you can use:</p>
<pre class="code">
<exec executable="/bin/sh">
<arg line='-c "m4 foo.m4 &gt; foo"'/>
</exec>
</pre>
<p>Note the double-quotes nested inside the single-quotes.</p>
<p class="faq">
<a name="batch-shell-execute"></a>
How do I execute a batch file or shell script from Ant?
</p>
<p>On native Unix systems, you should be able to run shell scripts
directly. On systems running a Unix-type shell (for example, Cygwin
on Windows) execute the (command) shell instead - <code>cmd</code>
for batch files, <code>sh</code> for shell scripts - then pass the
batch file or shell script (plus any arguments to the script)
as a single command, using the <code>/c</code> or
<code>-c</code> switch, respectively. See
<a href="#shell-redirect-2">the above section</a>
for example <code><exec></code> tasks
executing <code>sh</code>. For batch files, use something like:</p>
<pre class="code">
<exec dir="." executable="cmd" os="Windows NT">
<arg line="/c test.bat"/>
</exec>
</pre>
<p class="faq">
<a name="multi-conditions"></a>
I want to execute a particular target only if
multiple conditions are true.
</p>
<p>There are actually several answers to this question.</p>
<p>If you have only one set and one unset property to test,
you can specify both an <code>if</code> and an <code>unless</code>
attribute for the target, and they will act as if they
are "anded" together.</p>
<p>If you are using a version of Ant 1.3 or earlier, the
way to work with all other cases is to chain targets together
to determine the specific state you want to test for.</p>
<p>To see how this works, assume you have three properties:
<code>prop1</code>, <code>prop2</code>, and <code>prop3</code>.
You want to test that <code>prop1</code> and <code>prop2</code>
are set, and that <code>prop3</code> is not. If the condition
holds true you want to echo "yes".</p>
<p>Here is the implementation in Ant 1.3 and earlier:</p>
<pre class="code">
<target name="cond" depends="cond-if"/>
<target name="cond-if" if="prop1">
<antcall target="cond-if-2"/>
</target>
<target name="cond-if-2" if="prop2">
<antcall target="cond-if-3"/>
</target>
<target name="cond-if-3" unless="prop3">
<echo message="yes"/>
</target>
</pre>
<p>Note: <code><antcall></code> tasks do <em>not</em> pass
property changes back up to the environment they were called
from, so you wouldn't be able to, for example, set a
<code>result</code> property in the <code>cond-if-3</code> target,
then do
<code><echo message="result is ${result}"/></code>
in the <code>cond</code> target.</p>
<p>Starting with Ant 1.4, you can use the
<code><condition></code> task.</p>
<pre class="code">
<target name="cond" depends="cond-if,cond-else"/>
<target name="check-cond">
<condition property="cond-is-true">
<and>
<not>
<equals arg1="${prop1}" arg2="$${prop1}" />
</not>
<not>
<equals arg1="${prop2}" arg2="$${prop2}" />
</not>
<equals arg1="${prop3}" arg2="$${prop3}" />
</and>
</condition>
</target>
<target name="cond-if" depends="check-cond" if="cond-is-true">
<echo message="yes"/>
</target>
<target name="cond-else" depends="check-cond" unless="cond-is-true">
<echo message="no"/>
</target>
</pre>
<p>This version takes advantage of two things:</p>
<ul>
<li>If a property <code>a</code> has not been set,
<code>${a}</code> will evaluate to <code>${a}</code>.</li>
<li>To get a literal <code>$</code> in Ant, you have to
escape it with another <code>$</code> - this will also break
the special treatment of the <code>${</code> sequence.</li>
</ul>
<p>Because testing for a literal <code>${property}</code> string
isn't all that readable or easy to understand,
post-1.4.1 Ant introduces the <code><isset></code> element
to the <code><condition></code> task.</p>
<p>Here is the previous example done using
<code><isset></code>:</p>
<pre class="code">
<target name="check-cond">
<condition property="cond-is-true">
<and>
<isset property="prop1"/>
<isset property="prop2"/>
<not>
<isset property="prop3"/>
</not>
</and>
</condition>
</target>
</pre>
<p>The last option is to use a scripting language to set the
properties. This can be particularly handy when you need much
finer control than the simple conditions shown here but, of
course, comes with the overhead of adding JAR files to support
the language, to say nothing of the added maintenance in requiring
two languages to implement a single system. See the
<a href="manual/Tasks/script.html">
<code><script></code> task documentation</a> for more
details.</p>
<p class="faq">
<a name="encoding"></a>
How can I include national characters like German
umlauts in my build file?
</p>
<p>You need to tell the XML parser which character encoding
your build file uses, this is done inside the <a href="http://www.w3.org/TR/2000/REC-xml-20001006#sec-prolog-dtd">XML
declaration</a>.</p>
<p>By default the parser assumes you are using the UTF-8
encoding instead of your platform's default. For most Western
European countries you should set the encoding to
<code>ISO-8859-1</code>. To do so, make the very first line
of you build file read like</p>
<pre class="code">
<?xml version="1.0" encoding="ISO-8859-1" ?>
</pre>
<p class="faq">
<a name="use-zip-instead-of-jar"></a>
How do I use <code>jar</code>'s <code>M</code> switch?
I don't want a MANIFEST.
</p>
<p>A JAR archive is a ZIP file, so if you don't want a
MANIFEST you can simply use <code><zip></code>.</p>
<p>If your file names contain national characters you should
know that Sun's <code>jar</code> utility like Ant's
<code><jar></code> uses UTF-8 to encode their names while
<code><zip></code> uses your platforms default encoding.
Use the encoding attribute of <code><zip></code> if
necessary.</p>
<p class="faq">
<a name="propertyvalue-as-name-for-property"></a>
How can I do something like <code><property name="prop"
value="${${anotherprop}}"/></code> (double expanding the property)?
</p>
<p>Without any external help you can not.</p>
<p>With <script/>, which needs external libraries, you can do</p>
<pre class="code">
<script language="javascript">
propname = project.getProperty("anotherprop");
project.setNewProperty("prop", propname);
</script>
</pre>
<p>With AntContrib (external task library) you can do <code>
<propertycopy name="prop" from="${anotherprop}"/></code>.</p>
<p>With Ant 1.6 you can simulate the AntContribs <propertycopy>
and avoid the need of an external library:</p>
<pre class="code">
<macrodef name="propertycopy">
<attribute name="name"/>
<attribute name="from"/>
<sequential>
<property name="@{name}" value="${@{from}}"/>
</sequential>
</macrodef>
</pre>
<p>With the 'props' antlib (external, but also from Ant) you could
do the dereferencing with <code>${${anotherprop}</code> - not just
in the property task - instead everywhere in your buildfile (after
registering the required property helper).</p>
<pre class="code">
<propertyhelper>
<props:nested />
</propertyhelper>
<property name="foo" value="foo.value" />
<property name="var" value="foo" />
<echo> ${${var}} = foo.value </echo></pre>
<p class="faq">
<a name="delete-directory-children-only"></a>
How can I delete everything beneath a particular directory,
preserving the directory itself?
</p>
<p>Most users who go down this path have no problem figuring out that
<code><delete includeemptydirs="true" /></code> will help them. The
seemingly tricky part is preserving the base directory itself,
which Ant includes in the directory scan. Fortunately the answer is simple:
</p>
<pre class="code">
<delete includeemptydirs="true">
<fileset dir="dirtokeep" includes="**/*" />
</delete>
</pre>
<p class="faq">
<a name="delete-directory-only-if-empty"></a>
How can I delete a particular directory,
if and only if it is empty?
</p>
<p>Most users who go down this path have no problem figuring
out that
<code><delete includeemptydirs="true" /></code> will
help them. The seemingly tricky part is preserving the
non-empty directories, which Ant includes in the directory
scan. Fortunately the answer is simple:</p>
<pre class="code">
<delete includeemptydirs="true">
<fileset dir="dirtokeepifnotempty" excludes="**/*" />
</delete>
</pre>
<p class="faq">
<a name="general-advice"></a>
General Advice
</p>
<p>There are many reasons why Apache Ant doesn't behave as
expected, not all of them are due to Ant bugs. See our <a href="problems.html">Having Problems?</a> page for hints that
may help pinning down the reasons for your problem.</p>
<p class="faq">
<a name="always-recompiles"></a>
Why does Ant always recompile all my Java files?
</p>
<p>In order to find out which files should be compiled, Ant
compares the timestamps of the source files to those of the
resulting <code>.class</code> files. Opening all source files
to find out which package they belong to would be very
inefficient. Instead, Ant expects you to place your
source files in a directory hierarchy that mirrors your
package hierarchy and to point Ant to the root of this
directory tree with the <code>srcdir</code> attribute.</p>
<p>Say you have <code><javac srcdir="src"
destdir="dest"/></code>. If Ant finds a file
<code>src/a/b/C.java</code>, it expects it to be in package
<code>a.b</code> so that the resulting <code>.class</code>
file is going to be <code>dest/a/b/C.class</code>.</p>
<p>If your source-tree directory structure does not match your
package structure, Ant's heuristic won't work, and
it will recompile classes that are up-to-date. Ant is not the
only tool that expects a source-tree layout like this.</p>
<p>If you have Java source files that aren't declared to
be part of any package, you can still use the <code><javac></code>
task to compile these files correctly - just set the
<code>srcdir</code> and <code>destdir</code> attributes to
the actual directory the source
files live in and the directory the class files should go into,
respectively.</p>
<p class="faq">
<a name="defaultexcludes"></a>
I've used a <code><delete></code> task to
delete unwanted SourceSafe control files (CVS files, editor
backup files, etc.), but it doesn't seem to work; the files
never get deleted. What's wrong?
</p>
<p>This is probably happening because, by default, Ant excludes
SourceSafe control files (<code>vssver.scc</code>) and certain other
files from FileSets.</p>
<p>Here's what you probably did:</p>
<pre class="code">
<delete>
<fileset dir="${build.src}" includes="**/vssver.scc"/>
</delete>
</pre>
<p>You need to switch off the default exclusions,
and it will work:</p>
<pre class="code">
<delete>
<fileset dir="${build.src}" includes="**/vssver.scc"
defaultexcludes="no"/>
</delete>
</pre>
<p>For a complete listing of the patterns that are excluded
by default, see <a href="manual/dirtasks.html#defaultexcludes">the user
manual</a>.</p>
<p class="faq">
<a name="stop-dependency"></a>
I have a target I want to skip if a property is set,
so I have <code>unless="property"</code> as an attribute
of the target, but all the targets this target
depends on are still executed. Why?
</p>
<p>The list of dependencies is generated by Ant before any of the
targets are run. This allows dependent targets, such as an
<code>init</code> target, to set properties that can control the
execution of the targets higher in the dependency graph. This
is a good thing.</p>
<p>However, when your dependencies break down the
higher-level task
into several smaller steps, this behaviour becomes
counter-intuitive. There are a couple of solutions available:
</p>
<ol>
<li>Put the same condition on each of the dependent targets.</li>
<li>Execute the steps using <code><antcall></code>,
instead of specifying them inside the <code>depends</code>
attribute.</li>
</ol>
<p class="faq">
<a name="include-order"></a>
In my <code><fileset></code>, I've put in an
<code><exclude></code> of all files followed by an
<code><include></code> of just the files I want, but it
isn't giving me any files at all. What's wrong?
</p>
<p>The order of the <code><include></code> and
<code><exclude></code> tags within a <code><fileset></code>
is ignored when the FileSet is created. Instead, all of the
<code><include></code> elements are processed together,
followed by all of the <code><exclude></code>
elements. This means that the <code><exclude></code>
elements only apply to the file list produced by the
<code><include></code> elements.</p>
<p>To get the files you want, focus on just the
<code><include></code> patterns that would be necessary
to get them. If you find you need to trim the list that the
<code><include></code> elements produce, then use
<code><exclude></code> elements.</p>
<p class="faq">
<a name="properties-not-trimmed"></a>
<code>ant</code> failed to build my program via javac
even when I put the needed jars in an external
<code>build.properties</code> file and reference them by
<code>pathelement</code> or <code>classpath refid</code>.
</p>
<p>When <code>ant</code> loads properties from an external
file it doesn't touch the value of properties, trailing blanks
will not be trimmed for example.</p>
<p>If the value represents a file path, like a jar needed to
compile, the task which requires the value, javac for example
would fail to compile since it can't find the file due to
trailing spaces.</p>
<p class="faq">
<a name="winzip-lies"></a>
Ant creates WAR files with a lower-case
<code>web-inf</code> or JAR files with a lower-case
<code>meta-inf</code> directory.
</p>
<p>No it doesn't.</p>
<p>You may have seen these lower-case directory names in
WinZIP, but WinZIP is trying to be helpful (and fails). If
WinZIP encounters a filename that is all upper-case, it
assumes it has come from an old DOS box and changes the case to
all lower-case for you.</p>
<p>If you extract (or just check) the archive with jar, you
will see that the names have the correct case.</p>
<p>With WinZIP (version 8.1 at least), this can be corrected in the
configuration. In the Options/Configuration menu, in the View tab, General
section, check the "Allow all upper case files names" box. The META-INF and
WEB-INF will look correct.</p>
<p class="faq">
<a name="NoClassDefFoundError"></a>
I installed Ant 1.6.x and now get
<code>Exception in thread "main" java.lang.NoClassDefFoundError:
</code>
</p>
<p>
The cause of this is that there is an old version of ant somewhere in the
class path or configuration.
</p>
<p>
A version of this problem happens with jars that are in the classpath
that include an embedded copy of ant classes.
An example of this is some copies of weblogic.jar.
</p>
<p>
One can check if this is the case by doing (on unix/sh):
<code><pre>
unset CLASSPATH
ant -version
</pre>
</code>
</p>
<p class="faq">
<a name="InstantiationException"></a>
I installed Ant 1.6.x and now get
<code>java.lang.InstantiationException: org.apache.tools.ant.Main</code>
</p>
<p>
The cause of this is that there is an old version of ant somewhere in the
class path or configuration.
</p>
<p>
A version of this problem may be seen on some linux systems.
Some linux systems (Fedora Core 2 for example), comes with a version
of ant pre-installed. There is a configuration file called
<code>/etc/ant.conf</code> which if present, the ant shell
script will 'dot' include. On Fedora Core 2, the /etc/ant.conf
file resets the <code>ANT_HOME</code> environment variable to
<code>/usr/share/ant</code>. This causes the problem that
an old version of ant (1.5.x in this cause) will be used
with a new version of the ant script file.
</p>
<p>
One can check if this is the case by doing
<code>ant --noconfig -version</code>.
</p>
<p class="faq">
<a name="mangled-manifest"></a>
Whenever I use the Ant jar or manifest related tasks, long lines in
my manifest are wrapped at 70 characters and the resulting jar does
not work in my application server. Why does Ant do this?
</p>
<p>
Ant implements the Java
<a href="http://download.oracle.com/javase/1.4.2/docs/guide/jar/jar.html">Jar
file specification</a>. Please refer to the notes section where it
discusses the maximum allowable length of a line and the concept of
continuation characters.
</p>
<p>
If a jar file produced by Ant does not work in your appserver, and
that failure is due to the wrapped manifest, then you need
to consult your appserver provider, as it is a bug in their
appserver. Far more likely, however, is a problem in your
specification of your classpath. It is not Ant's wrapping of your
classpath that is the problem.
</p>
<p>
Do not raise a bug about this issue until you have checked to ensure
that the problem is not due to your classpath specification.
</p>
<p class="faq">
<a name="CreateProcess_error_2"></a>
<code><exec></code> fails with <code>"Cannot run
program "...":CreateProcess error=2"</code> on
Windows.
</p>
<p>A common problem is not having the executable on the
PATH. In case you get an error message <code>Cannot run
program "...":CreateProcess error=2. The system cannot find
the path specified.</code> have a look at your PATH
variable.</p>
<p>Just type the command directly on the command line and if
Windows finds it, Ant should do it too. (Otherwise ask on
the user mailinglist for help.) If Windows can not execute
the program add the directory of the programm to the PATH
(<code>set PATH=%PATH%;dirOfProgram</code>) or specify the
absolute path in the <code>executable</code> attribute in
your buildfile.</p>
<p class="faq">
<a name="integration"></a>
Is Apache Ant supported by my IDE/Editor?
</p>
<p>See the <a href="external.html#IDE and Editor Integration">section
on IDE integration</a> on our External Tools and Tasks page.</p>
<p class="faq">
<a name="emacs-mode"></a>
Why doesn't (X)Emacs/vi/MacOS X's project builder
correctly parse the error messages generated by Ant?
</p>
<p>Ant adds a "banner" with the name of the current
task in front of all logging messages - and there are no built-in
regular expressions in your editor that would account for
this.</p>
<p>You can disable this banner by invoking Ant with the
<code>-emacs</code> switch. To make Ant autodetect
Emacs' compile mode, put this into your
<code>.antrc</code> (contributed by Ville Skyttä).</p>
<pre class="code">
# Detect (X)Emacs compile mode
if [ "$EMACS" = "t" ] ; then
ANT_ARGS="$ANT_ARGS -emacs"
ANT_OPTS="$ANT_OPTS -Dbuild.compiler.emacs=true"
fi
</pre>
<p>Alternatively, you can add the following snippet to your
<code>.emacs</code> to make Emacs understand Ant's
output.</p>
<pre class="code">
(require 'compile)
(setq compilation-error-regexp-alist
(append (list
;; works for jikes
'("^\\s-*\\[[^]]*\\]\\s-*\\(.+\\):\\([0-9]+\\):\\([0-9]+\\):[0-9]+:[0-9]+:" 1 2 3)
;; works for javac
'("^\\s-*\\[[^]]*\\]\\s-*\\(.+\\):\\([0-9]+\\):" 1 2))
compilation-error-regexp-alist))
</pre>
<p>Yet another alternative that preserves most of Ant's
formatting is to pipe Ant's output through the following Perl
script by Dirk-Willem van Gulik:</p>
<pre class="code">
#!/usr/bin/perl
#
# May 2001 dirkx@apache.org - remove any
# [foo] lines from the output; keeping
# spacing more or less there.
#
$|=1;
while(<STDIN>) {
if (s/^(\s+)\[(\w+)\]//) {
if ($2 ne $last) {
print "$1\[$2\]";
$s = ' ' x length($2);
} else {
print "$1 $s ";
};
$last = $2;
};
print;
};
</pre>
<p class="faq">
<a name="dtd"></a>
Is there a DTD that I can use to validate my build
files?
</p>
<p>An incomplete DTD can be created by the
<code><antstructure></code> task - but this one
has a few problems:</p>
<ul>
<li>It doesn't know about required attributes. Only
manual tweaking of this file can help here.</li>
<li>It is not complete - if you add new tasks via
<code><taskdef></code> it won't know about it. See
<a href="http://www.sdv.fr/pages/casa/html/ant-dtd.en.html">this
page</a> by Michel Casabianca for a solution to this
problem. Note that the DTD you can download at this page
is based on Apache Ant 0.3.1.</li>
<li>It may even be an invalid DTD. As Ant allows tasks
writers to define arbitrary elements, name collisions will
happen quite frequently - if your version of Ant contains
the optional <code><test></code> and
<code><junit></code> tasks, there are two XML
elements named <code>test</code> (the task and the nested child
element of <code><junit></code>) with different attribute
lists. This problem cannot be solved; DTDs don't give a
syntax rich enough to support this.</li>
</ul>
<p class="faq">
<a name="xml-entity-include"></a>
How do I include an XML snippet in my build file?
</p>
<p>You can use XML's way of including external files and let
the parser do the job for Ant:</p>
<pre class="code">
<?xml version="1.0"?>
<!DOCTYPE project [
<!ENTITY common SYSTEM "common.xml">
]>
<project name="test" default="test" basedir=".">
<target name="setup">
...
</target>
&common;
...
</project>
</pre>
<p>will literally include the contents of <code>common.xml</code> where
you've placed the <code>&common;</code> entity.</p>
<p>(The filename <code>common.xml</code> in this example is resolved
relative to the containing XML file by the XML parser. You may also use
an absolute <code>file:</code> protocol URI.)</p>
<p>In combination with a DTD, this would look like this:</p>
<pre class="code">
<!DOCTYPE project PUBLIC "-//ANT//DTD project//EN" "ant.dtd" [
<!ENTITY include SYSTEM "header.xml">
]>
</pre>
<p>Starting with Ant 1.6, there is a new
<code><import></code> task that can (also) be used to
include build file fragments. Unlike the snippets used with
entity includes, the referenced files have to be complete Ant
build files, though.</p>
<p>The example above would become:</p>
<pre class="code">
<?xml version="1.0"?>
<project name="test" default="test" basedir=".">
<target name="setup">
...
</target>
<import file="./common.xml"/>
...
</project>
</pre>
<p>Unlike entity includes, <code><import></code> will
let you use Ant properties in the file name.</p>
<p class="faq">
<a name="mail-logger"></a>
How do I send an email with the result of my build
process?
</p>
<p>If you are using a nightly build of Ant 1.5 after
2001-12-14, you can use the built-in MailLogger:</p>
<pre class="code">
ant -logger org.apache.tools.ant.listener.MailLogger
</pre>
<p>See the <a href="http://svn.apache.org/repos/asf/ant/core/trunk/docs/manual/listeners.html">Listeners
& Loggers</a> documentation for details on the properties
required.</p>
<p>For older versions of Ant, you can use a custom
BuildListener that sends out an email
in the buildFinished() method. Will Glozer
<will.glozer@jda.com> has written such a listener based
on <a href="http://www.oracle.com/technetwork/java/index-jsp-139225.html">JavaMail</a>.
The source is:</p>
<pre class="code">
import java.io.*;
import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;
import org.apache.tools.ant.*;
/**
* A simple listener that waits for a build to finish and sends an email
* of the results. The settings are stored in "monitor.properties" and
* are fairly self explanatory.
*
* @author Will Glozer
* @version 1.05a 09/06/2000
*/
public class BuildMonitor implements BuildListener {
protected Properties props;
/**
* Create a new BuildMonitor.
*/
public BuildMonitor() throws Exception {
props = new Properties();
InputStream is = getClass().getResourceAsStream("monitor.properties");
props.load(is);
is.close();
}
public void buildStarted(BuildEvent e) {
}
/**
* Determine the status of the build and the actions to follow, now that
* the build has completed.
*
* @param e Event describing the build status.
*/
public void buildFinished(BuildEvent e) {
Throwable th = e.getException();
String status = (th != null) ? "failed" : "succeeded";
try {
String key = "build." + status;
if (props.getProperty(key + ".notify").equalsIgnoreCase("false")) {
return;
}
Session session = Session.getDefaultInstance(props, null);
MimeMessage message = new MimeMessage(session);
message.addRecipients(Message.RecipientType.TO, parseAddresses(
props.getProperty(key + ".email.to")));
message.setSubject(props.getProperty(key + ".email.subject"));
BufferedReader br = new BufferedReader(new FileReader(
props.getProperty("build.log")));
StringWriter sw = new StringWriter();
String line = br.readLine();
while (line != null) {
sw.write(line);
sw.write("\n");
line = br.readLine();
}
br.close();
message.setText(sw.toString(), "UTF-8");
sw.close();
Transport transport = session.getTransport();
transport.connect();
transport.send(message);
transport.close();
} catch (Exception ex) {
System.out.println("BuildMonitor failed to send email!");
ex.printStackTrace();
}
}
/**
* Parse a comma separated list of internet email addresses.
*
* @param s The list of addresses.
* @return Array of Addresses.
*/
protected Address[] parseAddresses(String s) throws Exception {
StringTokenizer st = new StringTokenizer(s, ",");
Address[] addrs = new Address[st.countTokens()];
for (int i = 0; i < addrs.length; i++) {
addrs[i] = new InternetAddress(st.nextToken());
}
return addrs;
}
public void messageLogged(BuildEvent e) {
}
public void targetStarted(BuildEvent e) {
}
public void targetFinished(BuildEvent e) {
}
public void taskStarted(BuildEvent e) {
}
public void taskFinished(BuildEvent e) {
}
}
</pre>
<p>With a <code>monitor.properties</code> like this:</p>
<pre class="code">
# configuration for build monitor
mail.transport.protocol=smtp
mail.smtp.host=<host>
mail.from=Will Glozer <will.glozer@jda.com>
build.log=build.log
build.failed.notify=true
build.failed.email.to=will.glozer@jda.com
build.failed.email.subject=Nightly build failed!
build.succeeded.notify=true
build.succeeded.email.to=will.glozer@jda.com
build.succeeded.email.subject=Nightly build succeeded!
</pre>
<p><code>monitor.properties</code> should be placed right next
to your compiled <code>BuildMonitor.class</code>. To use it,
invoke Ant like:</p>
<pre class="code">
ant -listener BuildMonitor -logfile build.log
</pre>
<p>Make sure that <code>mail.jar</code> from JavaMail and
<code>activation.jar</code> from the
<a href="http://www.oracle.com/technetwork/java/javase/jaf-135115.html">Java
Beans Activation Framework</a> are in your <code>CLASSPATH</code>.</p>
<p class="faq">
<a name="listener-properties"></a>
How do I get at the properties that Ant was running
with from inside BuildListener?
</p>
<p>You can get at a hashtable with all the properties that Ant
has been using through the BuildEvent parameter. For
example:</p>
<pre class="code">
public void buildFinished(BuildEvent e) {
Hashtable table = e.getProject().getProperties();
String buildpath = (String)table.get("build.path");
...
}
</pre>
<p>This is more accurate than just reading the same property
files that your project does, since it will give the correct
results for properties that were specified on the Ant command line.</p>
<p class="faq">
<a name="input-makes-exec-hang"></a>
<code><exec></code> causes other tasks to hang
or leads to strange behaviour of <code><input></code>
tasks.
</p>
<p>When Apache Ant forks a new process for example by using the
<code><exec></code>, <code><apply></code>
or <code><java></code> tasks, it will also start a
new thread reading from standard input and sending
everything that it has read to that process.</p>
<p>Unfortunately Ant has no way to know whether the forked
process is ever going to read any input, so it will start such
a thread even if the process doesn't need one.</p>
<p>This behaviour leads to strange side effects like the Ant
process
being <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=34461">suspended
when a build forking new process is run as a background
process</a> on Unix-like systems or
<code><input></code>
tasks <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=41024">requiring
additional inputs</a> if they come after
an <code><exec></code> task.</p>
<p>Fortunately there is a workaround for this, always specify
<code>inputstring=""</code> for
any <code><exec></code> task (or one of its sibblings)
if you know the forked process doesn't consume any
input.</p>
<p class="faq">
<a name="javac-stackoverflow"></a>
<code><javac></code> causes a
StackOverflowError
</p>
<p>For some Java source files it is possible
that <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=45370">causes
a StackOverlowError</a> is thrown inside Sun's javac
compiler. As far as we can tell this is not triggered by a
bug in Ant.</p>
<p>It is possible to work around this problem by setting
<code><javac></code>'s fork attribute to true.</p>
<p class="faq">
<a name="170-requires-junit"></a>
Ant 1.7.0 doesn't build from sources without
JUnit
</p>
<p>When building Ant 1.7.0 from the source release without
junit.jar the build fails with the message "We cannot build
the test jar unless JUnit is present".</p>
<p>With Ant 1.7.0 we've started to add ant-testutil.jar as
part of the distribution and this causes a hard dependency on
JUnit - at least in version 1.7.0. Unfortunately the
installation docs don't say so.</p>
<p>There are two workarounds:</p>
<ol>
<li>Add junit.jar to your CLASSPATH when building Ant.</li>
<li>Change Ant's buildfile and remove test-jar from the
depends list of the dist-lite target.</li>
</ol>
<p class="faq">
<a name="remove-cr"></a>
<chmod> or <exec> doesn't work in Ant
1.3 on Unix
</p>
<p>The <code>antRun</code> script in <code>ANT_HOME/bin</code>
has DOS instead of Unix line endings; you must remove the
carriage-return characters from this file. This can be done by
using Ant's <code><fixcrlf></code> task
or something like:</p>
<pre class="code">
tr -d '\r' < $ANT_HOME/bin/antRun > /tmp/foo
mv /tmp/foo $ANT_HOME/bin/antRun
</pre>
<p class="faq">
<a name="delegating-classloader"></a>
<style> or <junit> ignores my
<classpath>
</p>
<p>Starting with Ant 1.7.0, <junit> will honor your
nested <classpath>.</p>
<p>These tasks don't ignore your classpath setting, you
are facing a common problem with delegating classloaders.</p>
<p>This question collects a common type of problem: A task
needs an external library and it has a nested classpath
element so that you can point it to this external library, but
that doesn't work unless you put the external library
into the <code>CLASSPATH</code> or place it in
<code>ANT_HOME/lib</code>.</p>
<p>Some background is necessary before we can discuss
solutions for <a href="#delegating-classloader-1.5">Ant
1.5.x</a> and <a href="#delegating-classloader-1.6">Ant
1.6.x</a>.</p>
<p>When you specify a nested <code><classpath></code> in
Ant, Ant creates a new class loader that uses the path you
have specified. It then tries to load additional classes from
this classloader.</p>
<p>In most cases - for example using <style> or
<junit> - Ant doesn't load the external library
directly, it is the loaded class that does so.</p>
<p>In the case of <code><junit></code> it is the task
implementation itself and in the case of
<code><style></code> it is the implementation of the
<code>org.apache.tools.ant.taskdefs.XSLTLiaison</code>
class.</p>
<p><em>As of Ant 1.7</em> <code><junit></code> no longer
requires you to have <code>junit.jar</code> in Ant's startup
classpath even if <code>ant-junit.jar</code> is present there.</p>
<p>Ant's class loader implementation uses Java's
delegation model, see <a href="http://download.oracle.com/javase/6/docs/api/java/lang/ClassLoader.html">http://download.oracle.com/javase/6/docs/api/java/lang/ClassLoader.html</a>
the paragraph</p>
<blockquote>The <code>ClassLoader</code> class uses a
delegation model to search for classes and resources. Each
instance of <code>ClassLoader</code> has an associated parent
class loader. When called upon to find a class or resource, a
<code>ClassLoader</code> instance will delegate the search for
the class or resource to its parent class loader before
attempting to find the class or resource itself. The virtual
machine's built-in class loader, called the bootstrap
class loader, does not itself have a parent but may serve as
the parent of a <code>ClassLoader</code>
instance.</blockquote>
<p>The possible solutions depend on the version of Ant you
use, see the next sections.</p>
<p class="faq">
<a name="delegating-classloader-1.5"></a>
<style> or <junit> ignores my
<classpath> - Ant 1.5.x version
</p>
<p>Please read <a href="#delegating-classloader">the previous
entry</a> before you go ahead.</p>
<p>First of all let's state that Ant's wrapper script
(<code>ant</code> or <code>ant.bat</code>) adds all
<code>.jar</code> files from <code>ANT_HOME/lib</code> to
<code>CLASSPATH</code>, therefore "in
<code>CLASSPATH</code>" shall mean "either in your
<code>CLASSPATH</code> environment variable or
<code>ANT_HOME/lib</code>" for the rest of this
answer.</p>
<p>The root of the problem is that the class that needs the
external library is on the <code>CLASSPATH</code>.</p>
<p>Let's see what happens when you load the <junit>
task. Ant's class loader will consult the
bootstrap class loader first, which tries to load classes from
<code>CLASSPATH</code>. The bootstrap class loader
doesn't know anything about Ant's class loader or
even the path you have specified.</p>
<p>If the bootstrap class loader can load the class Ant has
asked it to load (which it can if <code>optional.jar</code> is
part of <code>CLASSPATH</code>), this class will try to load
the external library from <code>CLASSPATH</code> as well - it
doesn't know anything else - and will not find it unless
the library is in <code>CLASSPATH</code> as well.</p>
<p>To solve this, you have two major options:</p>
<ol>
<li>put all external libraries you need in
<code>CLASSPATH</code> as well this is not what you want,
otherwise you wouldn't have found this FAQ entry.</li>
<li>remove the class that loads the external library from
the <code>CLASSPATH</code>.</li>
</ol>
<p>The easiest way to do this is to remove
<code>optional.jar</code> from <code>ANT_HOME/lib</code>. If
you do so, you will have to <code><taskdef></code> all
optional tasks and use nested <code><classpath></code>
elements in the <code><taskdef></code> tasks that point
to the new location of <code>optional.jar</code>. Also,
don't forget to add the new location of
<code>optional.jar</code> to the
<code><classpath></code> of your
<code><style></code> or <code><junit></code>
task.</p>
<p>If you want to avoid to <code><taskdef></code> all
optional tasks you need, the only other option is to remove
the classes that should not be loaded via the bootstrap class
loader from <code>optional.jar</code> and put them into a
separate archive. Add this separate archive to the
<code><classpath></code> of your
<code><style></code> or <code><junit></code> task
- and make sure the separate archive is not in
<code>CLASSPATH</code>.</p>
<p>In the case of <code><junit></code> you'd have
to remove all classes that are in the
<code>org/apache/tools/ant/taskdefs/optional/junit</code>
directory, in the <code><style></code> case it is one of
the <code>*Liaison</code> classes in
<code>org/apache/tools/ant/taskdefs/optional</code>.</p>
<p>If you use the option to break up <code>optional.jar</code>
for <code><junit></code> or remove
<code>ant-junit.jar</code>, you still have to use a
<code><taskdef></code> with a nested
<code><classpath></code> to define the junit task.</p>
<p class="faq">
<a name="delegating-classloader-1.6"></a>
<style> or <junit> ignores my
<classpath> - Ant 1.6.x version
</p>
<p>Please read <a href="#delegating-classloader">the general
entry</a> before you go ahead.</p>
<p>The wrapper script of Ant 1.6.x no longer adds the contents
of <code>ANT_HOME/lib</code> to <code>CLASSPATH</code>,
instead Ant will create a classloader on top of the bootstrap
classloader - let's call it the coreloader for the rest of
this answer - which holds the contents of
<code>ANT_HOME/lib</code>. Ant's core and its tasks will be
loaded through this classloader and not the bootstrap
classloader.</p>
<p>This causes some small but notable differences between Ant
1.5.x and 1.6.x. Most importantly, a third-party task that is
part of <code>CLASSPATH</code> will no longer work in Ant
1.6.x since the task now can't find Ant's classes. In a sense
this is the same problem this entry is about, only
<code>ant.jar</code> has become the external library in
question now.</p>
<p>This coreloader also holds the contents of
<code>~/.ant/lib</code> and any file or directory that has
been specified using Ant's <code>-lib</code> command line
argument.</p>
<p>Let's see what happens when you load the <junit>
task. Ant's class loader will consult the bootstrap
class loader first, which tries to load classes from
<code>CLASSPATH</code>. The bootstrap class loader
doesn't know anything about Ant's class loader or
even the path you have specified. If it fails to find the
class using the bootstrap classloader it will try the
coreloader next. Again, the coreloader doesn't know anything
about your path.</p>
<p>If the coreloader can load the class Ant has asked it to
load (which it can if <code>ant-junit.jar</code> is in
<code>ANT_HOME/lib</code>), this class will try to load the
external library from coreloader as well - it doesn't
know anything else - and will not find it unless the library
is in <code>CLASSPATH</code> or the coreloader as well.</p>
<p>To solve this, you have the following major options:</p>
<ol>
<li>put all external libraries you need in
<code>CLASSPATH</code> as well this is not what you want,
otherwise you wouldn't have found this FAQ entry.</li>
<li>put all external libraries you need in
<code>ANT_HOME/lib</code> or <code>.ant/lib</code>. This
probably still isn't what you want, but you might reconsider
the <code>.ant/lib</code> option.</li>
<li>Always start Ant with the <code>-lib</code> command line
switch and point to your external libraries (or the
directories holding them).</li>
<li>remove the class that loads the external library from
the coreloader.</li>
</ol>
<p>In Ant 1.6 <code>optional.jar</code> has been split into
multiple jars, each one containing classes with the same
dependencies on external libraries. You can move the
"offending" jar out of <code>ANT_HOME/lib</code>. For the
<code><junit></code> task it would be
<code>ant-junit.jar</code>.</p>
<p>If you do so, you will have to <code><taskdef></code>
all optional tasks that need the external library and use
nested <code><classpath></code> elements in the
<code><taskdef></code> tasks that point to the new
location of <code>ant-*.jar</code>. Also, don't forget
to add the new location of <code>ant-*.jar</code> to the
<code><classpath></code> of your
<code><style></code> or <code><junit></code>
task.</p>
<p>For example</p>
<pre class="code">
<taskdef name="junit"
class="org.apache.tools.ant.taskdefs.optional.junit.JUnitTask">
<classpath>
<pathelement location="HOME-OF/junit.jar"/>
<pathelement location="NEW-HOME-OF/ant-junit.jar"/>
</classpath>
</taskdef>
</pre>
<p class="faq">
<a name="unknownelement.taskcontainer"></a>
Why do my custom task containers see Unknown Elements in Ant 1.6
- they worked in Ant 1.5?
</p>
<p>
The objects added in TaskContainer.addTask(Task task)
have changed from Tasks to UnknownElements.
</p>
<p>
There was a number of valid reasons for this change. But the backward
compatibility problems were not noticed until after Ant 1.6.0 was
released.
</p>
<p>
Your container class will need to be modified to check if the Task
is an UnknownElement and call perform on it to
convert it to a Task and to execute it.
(see apache.tools.ant.taskdefs.Sequential)
</p>
<p>
If you want to do more processing on the task,
you need to use the techniques in apache.tools.ant.taskdefs.Antlib#execute()
This does make use of one 1.6 method call (UE#getRealObject()),
you need to use UE#getTask() instead - this will
return null for non tasks (types like fileset id=x).
</p>
<p>
So.. iterate over the tasks, if they are UEs, convert them to
tasks, using UE#maybeConfigure and UE#getTask()
</p>
<pre class="code">
for (Iterator i = tasks.iterator(); i.hasNext();) {
Task t = (Task) i.next();
if (t instanceof UnknownElement) {
((UnknownElement) t).maybeConfigure();
t = ((UnknownElement) t).getTask();
if (t == null) {
continue;
}
}
// .... original Custom code
}
</pre>
<p>
This approach should work for ant1.5 and ant1.6.
</p>
<p class="faq">
<a name="oom-on-mac"></a>
Ant runs into an infinite loop/throws an OutOfMemoryError
when I compile my project under Mac OS X.
</p>
<p>Apple's Java VMs reside
in <code>/System/Library/Frameworks/JavaVM.framework/Versions/X.Y.Z</code>
and <code>JAVA_HOME</code> will usually be something
like <code>/System/Library/Frameworks/JavaVM.framework/Versions/X.Y.Z/Home</code>.</p>
<p>Inside this home directory there is a symbolic link
named <code>shared_bundle</code> that links three levels up,
i.e. to <code>/System/Library/Frameworks/JavaVM.framework</code>.</p>
<p>If your build file contains a <code>fileset</code> like</p>
<pre class="code">
<fileset dir="${java.home}" includes="**/*.jar"/>
</pre>
<p>Ant is going to follow the <code>shared_bundle</code>
symlink and ends up recursing into all your installed VMs.
Even worse, it will
enter <code>/System/Library/Frameworks/JavaVM.framework/Versions/X.Y.Z/Home</code>
and will once again follow the same symlink.</p>
<p>Ant versions after Ant 1.7.1 will detect the infinite loop
they are in, but the resulting fileset may still be too big to
deal with, in particular if you have many different VM
versions installed. The problem is amplified by the fact that
each installed version has a <code>shared_bundle</code>
symlink in it.</p>
<p>One solution is to not allow the fileset to follow symbolic
links at all, like in</p>
<pre class="code">
<fileset dir="${java.home}" includes="**/*.jar" followsymlinks="false"/>
</pre>
<p>another one excludes the <code>shared_bundle</code>
directories:</p>
<pre class="code">
<fileset dir="${java.home}" includes="**/*.jar" excludes="**/shared_bundle/**"/>
</pre>
<p>For Ant 1.7.1 and earlier
excluding <code>shared_bundle</code> may not be enough since
there is another symlink <code>bundle</code> that points to
the <code>Home</code> directory and will cause infite
recursions as well.</p>
<p class="faq">
<a name="extension-point-and-import"></a>
<code>extension-point</code> doesn't work
with <code>import</code> like the documentation
states.
</p>
<p>Yes, there is
a <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=48804">bug
in Ant 1.8.0</a>.</p>
<p>When using two build files like</p>
<pre class="code">
importing.xml:
<project>
...
<import file="imported.xml"/>
<target name="bar" extensionOf="foo"/>
</project>
imported.xml:
<project>
<extension-point name="foo"/>
</project>
</pre>
<p>Ant 1.8.0 will fail, claiming there was no extension point
named "foo".</p>
<p>This bug has been fixed for Ant 1.8.1. For Ant 1.8.0 there
is
a <a href="https://issues.apache.org/bugzilla/show_bug.cgi?id=48804#c9">work-around</a>:
add an additional layer of importing like in</p>
<pre class="code">
importing.xml:
<project>
<target name="bar" extensionOf="foo"/>
</project>
imported.xml:
<project>
<extension-point name="foo"/>
</project>
build.xml:
<project>
<import file="imported.xml"/>
<import file="importing.xml"/>
</project>
</pre>
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