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Partly rewrite the delegating-classloader FAQ since 1.5.x and 1.6.x are really quite a bit different 

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@278223 13f79535-47bb-0310-9956-ffa450edef68
master
Stefan Bodewig 20 years ago
parent
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commit
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4 changed files with 272 additions and 75 deletions
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  1. +1
    -1
      docs/contributors.html
  2. +5
    -5
      docs/external.html
  3. +128
    -33
      docs/faq.html
  4. +138
    -36
      xdocs/faq.xml

+ 1
- 1
docs/contributors.html View File

@@ -334,7 +334,7 @@ on Ant as a build tool.
Martijn Kruithof is a system engineer working with and on Java products
in a telecommunication network setting.
</p>
<p>
<p>
<b>Alexey Solofnenko</b> (trelony at gmail.com)<br />
</p>
<h4 class="subsection">


+ 5
- 5
docs/external.html View File

@@ -6134,11 +6134,11 @@
</tr>
</table>
<h4 class="subsection">
<a name="NetBeans / Sun ONE Studio"></a>
NetBeans / Sun ONE Studio
<a name="NetBeans"></a>
NetBeans
</h4>
<p>A module that integrates Ant into the NetBeans or Sun Java Studio (formerly
Forte for Java and Sun ONE Studio) IDEs.</p>
<p>A module that integrates Ant into the NetBeans IDE, as well as derivative products such as Sun Java
Studio (formerly Forte for Java and Sun ONE Studio) and Sun Java Studio Creator.</p>
<table class="externals" cellspacing="1" cellpadding="4">
<tr>
<th colspan="1" rowspan="1"
@@ -6147,7 +6147,7 @@
</th>
<td colspan="1" rowspan="1"
valign="top" align="left">
bundles Ant 1.6.2 as of NetBeans 4.0
bundles Ant 1.6.2 as of NetBeans 4.1; 1.6.3 for NetBeans 4.2 (will be made available as a 4.1 update)
</td>
</tr>
<tr>


+ 128
- 33
docs/faq.html View File

@@ -353,6 +353,14 @@
<li><a href="#delegating-classloader">
&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt;
</a></li>
<li><a href="#delegating-classloader-1.5">
&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - Ant 1.5.x version
</a></li>
<li><a href="#delegating-classloader-1.6">
&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - Ant 1.6.x version
</a></li>
<li><a href="#winxp-jdk14-ant14">
When running Ant 1.4 on Windows XP and JDK 1.4, I get
@@ -1610,31 +1618,23 @@ mv /tmp/foo $ANT_HOME/bin/antRun
</p>
<p>These tasks don't ignore your classpath setting, you
are facing a common problem with delegating classloaders.</p>
<p>First of all let's state that Ant 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>Technically the sentence above isn't true for Ant 1.6
and later anymore, but the result is the same. For the sake
of this discussion, <code>CLASSPATH</code> and
<code>ANT_HOME/lib</code> are identical.</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>.</p>
<p>The root of the problem is that the class that needs the
external library is on the <code>CLASSPATH</code>.</p>
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>&lt;classpath&gt;</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 the two cases above - Ant
doesn't load the external library directly, it is the loaded
class that does so.</p>
<p>In most cases - for example using &lt;style&gt; or
&lt;junit&gt; - Ant doesn't load the external library
directly, it is the loaded class that does so.</p>
<p>In the case of <code>&lt;junit&gt;</code> it is the task
implementation itself and in the case of
<code>&lt;style&gt;</code> it is the implementation of the
@@ -1654,16 +1654,37 @@ mv /tmp/foo $ANT_HOME/bin/antRun
class loader, does not itself have a parent but may serve as
the parent of a <code>ClassLoader</code>
instance.</blockquote>
<p>This means, Ant's class loader will consult the
<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>
&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - 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 &lt;junit&gt;
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, 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>
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
@@ -1673,8 +1694,6 @@ mv /tmp/foo $ANT_HOME/bin/antRun
<li>remove the class that loads the external library from
the <code>CLASSPATH</code>.</li>
</ol>
<p><strong>Using The Second Option with Ant 1.5.4 and
Earlier:</strong></p>
<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>&lt;taskdef&gt;</code> all
@@ -1701,22 +1720,98 @@ mv /tmp/foo $ANT_HOME/bin/antRun
directory, in the <code>&lt;style&gt;</code> case it is one of
the <code>*Liaison</code> classes in
<code>org/apache/tools/ant/taskdefs/optional</code>.</p>
<p><strong>Using The Second Option with Ant 1.6 and
later:</strong></p>
<p>If you use the option to break up <code>optional.jar</code>
for <code>&lt;junit&gt;</code> or remove
<code>ant-junit.jar</code>, you still have to use a
<code>&lt;taskdef&gt;</code> with a nested
<code>&lt;classpath&gt;</code> to define the junit task.</p>
<p class="faq">
<a name="delegating-classloader-1.6"></a>
&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - 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 &lt;junit&gt;
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 ANT_HOME/lib. For the
"offending" jar out of <code>ANT_HOME/lib</code>. For the
<code>&lt;junit&gt;</code> task it would be
<code>ant-junit.jar</code> and for <code>&lt;style&gt;</code>
it would be <code>ant-trax.jar</code>,
<code>ant-xalan1.jar</code> or <code>ant-xslp.jar</code> -
depending on the processor you use.</p>
<p>If you use the option to break up <code>optional.jar</code>
for <code>&lt;junit&gt;</code> or remove
<code>ant-junit.jar</code>, you still have to use a
<code>&lt;taskdef&gt;</code> with a nested
<code>&lt;classpath&gt;</code> to define the junit task.</p>
<p>If you do so, you will have to <code>&lt;taskdef&gt;</code>
all optional tasks that need the external libary and use
nested <code>&lt;classpath&gt;</code> elements in the
<code>&lt;taskdef&gt;</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>&lt;classpath&gt;</code> of your
<code>&lt;style&gt;</code> or <code>&lt;junit&gt;</code>
task.</p>
<p>For example</p>
<pre class="code">
&lt;taskdef name=&quot;junit&quot;
class=&quot;org.apache.tools.ant.taskdefs.optional.junit.JUnitTask&quot;&gt;
&lt;classpath&gt;
&lt;pathelement location=&quot;HOME-OF/junit.jar&quot;/&gt;
&lt;pathelement location=&quot;NEW-HOME-OF/ant-junit.jar&quot;/&gt;
&lt;/classpath&gt;
&lt;/taskdef&gt;
</pre>
<p class="faq">
<a name="winxp-jdk14-ant14"></a>
When running Ant 1.4 on Windows XP and JDK 1.4, I get


+ 138
- 36
xdocs/faq.xml View File

@@ -1346,36 +1346,26 @@ mv /tmp/foo $ANT_HOME/bin/antRun
<p>These tasks don&apos;t ignore your classpath setting, you
are facing a common problem with delegating classloaders.</p>

<p>First of all let&apos;s state that Ant adds all
<code>.jar</code> files from <code>ANT_HOME/lib</code> to
<code>CLASSPATH</code>, therefore &quot;in
<code>CLASSPATH</code>&quot; shall mean &quot;either in your
<code>CLASSPATH</code> environment variable or
<code>ANT_HOME/lib</code>&quot; for the rest of this
answer.</p>

<p>Technically the sentence above isn&apos;t true for Ant 1.6
and later anymore, but the result is the same. For the sake
of this discussion, <code>CLASSPATH</code> and
<code>ANT_HOME/lib</code> are identical.</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&apos;t work unless you put the external library into the
<code>CLASSPATH</code>.</p>
that doesn&apos;t work unless you put the external library
into the <code>CLASSPATH</code> or place it in
<code>ANT_HOME/lib</code>.</p>

<p>The root of the problem is that the class that needs the
external library is on the <code>CLASSPATH</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>&lt;classpath&gt;</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 the two cases above - Ant
doesn&apos;t load the external library directly, it is the loaded
class that does so.</p>
<p>In most cases - for example using &lt;style&gt; or
&lt;junit&gt; - Ant doesn&apos;t load the external library
directly, it is the loaded class that does so.</p>

<p>In the case of <code>&lt;junit&gt;</code> it is the task
implementation itself and in the case of
@@ -1400,17 +1390,45 @@ mv /tmp/foo $ANT_HOME/bin/antRun
the parent of a <code>ClassLoader</code>
instance.</blockquote>

<p>This means, Ant&apos;s class loader will consult the
<p>The possible solutions depend on the version of Ant you
use, see the next sections.</p>
</answer>
</faq>

<faq id="delegating-classloader-1.5">
<question>&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - Ant 1.5.x version</question>

<answer>

<p>Please read <a href="#delegating-classloader">the previous
entry</a> before you go ahead.</p>

<p>First of all let&apos;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 &quot;in
<code>CLASSPATH</code>&quot; shall mean &quot;either in your
<code>CLASSPATH</code> environment variable or
<code>ANT_HOME/lib</code>&quot; 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 &lt;junit&gt;
task. Ant&apos;s class loader will consult the
bootstrap class loader first, which tries to load classes from
<code>CLASSPATH</code>. The bootstrap class loader
doesn&apos;t know anything about Ant&apos;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, this class will try to load the external
library from <code>CLASSPATH</code> as well - it doesn&apos;t
know anything else - and will not find it unless the library
is in <code>CLASSPATH</code> as well.</p>
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&apos;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>

@@ -1423,9 +1441,6 @@ mv /tmp/foo $ANT_HOME/bin/antRun
the <code>CLASSPATH</code>.</li>
</ol>

<p><strong>Using The Second Option with Ant 1.5.4 and
Earlier:</strong></p>

<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>&lt;taskdef&gt;</code> all
@@ -1455,24 +1470,111 @@ mv /tmp/foo $ANT_HOME/bin/antRun
the <code>*Liaison</code> classes in
<code>org/apache/tools/ant/taskdefs/optional</code>.</p>

<p><strong>Using The Second Option with Ant 1.6 and
later:</strong></p>
<p>If you use the option to break up <code>optional.jar</code>
for <code>&lt;junit&gt;</code> or remove
<code>ant-junit.jar</code>, you still have to use a
<code>&lt;taskdef&gt;</code> with a nested
<code>&lt;classpath&gt;</code> to define the junit task.</p>
</answer>
</faq>

<faq id="delegating-classloader-1.6">
<question>&lt;style&gt; or &lt;junit&gt; ignores my
&lt;classpath&gt; - Ant 1.6.x version</question>

<answer>
<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 &lt;junit&gt;
task. Ant&apos;s class loader will consult the bootstrap
class loader first, which tries to load classes from
<code>CLASSPATH</code>. The bootstrap class loader
doesn&apos;t know anything about Ant&apos;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&apos;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&apos;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 ANT_HOME/lib. For the
"offending" jar out of <code>ANT_HOME/lib</code>. For the
<code>&lt;junit&gt;</code> task it would be
<code>ant-junit.jar</code> and for <code>&lt;style&gt;</code>
it would be <code>ant-trax.jar</code>,
<code>ant-xalan1.jar</code> or <code>ant-xslp.jar</code> -
depending on the processor you use.</p>

<p>If you use the option to break up <code>optional.jar</code>
for <code>&lt;junit&gt;</code> or remove
<code>ant-junit.jar</code>, you still have to use a
<code>&lt;taskdef&gt;</code> with a nested
<code>&lt;classpath&gt;</code> to define the junit task.</p>
<p>If you do so, you will have to <code>&lt;taskdef&gt;</code>
all optional tasks that need the external libary and use
nested <code>&lt;classpath&gt;</code> elements in the
<code>&lt;taskdef&gt;</code> tasks that point to the new
location of <code>ant-*.jar</code>. Also, don&apos;t forget
to add the new location of <code>ant-*.jar</code> to the
<code>&lt;classpath&gt;</code> of your
<code>&lt;style&gt;</code> or <code>&lt;junit&gt;</code>
task.</p>

<p>For example</p>
<source><![CDATA[
<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>
]]></source>
</answer>
</faq>



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