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@@ -288,6 +288,10 @@ |
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</a></li> |
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<li><a href="#javadoc-cannot-execute"> |
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JavaDoc failed: java.io.IOException: javadoc: cannot execute |
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</a></li> |
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<li><a href="#delegating-classloader"> |
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<style> or <junit> ignores my |
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<classpath> |
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</a></li> |
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</ul> |
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</blockquote> |
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@@ -1873,6 +1877,113 @@ mv /tmp/foo $ANT_HOME/bin/antRun |
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</blockquote> |
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</td></tr> |
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</table> |
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</a> |
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<a name="delegating-classloader"> |
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<table border="0" cellspacing="0" cellpadding="2" width="100%"> |
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<tr><td bgcolor="#828DA6"> |
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<font color="#ffffff" face="arial,helvetica,sanserif"> |
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<strong> |
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<style> or <junit> ignores my |
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<classpath> |
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</strong> |
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</font> |
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</td></tr> |
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<tr><td> |
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<blockquote> |
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<p>These tasks don't ignore your classpath setting, you |
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are facing a common problem with delegating classloaders.</p> |
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<p>First of all let's state that Ant adds all |
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<code>.jar</code> files from <code>ANT_HOME/lib</code> to |
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<code>CLASSPATH</code>, therefore "in |
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<code>CLASSPATH</code>" shall mean "either in your |
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<code>CLASSPATH</code> environment variable or |
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<code>ANT_HOME/lib</code>" for the rest of this |
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answer.</p> |
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<p>This question collects a common type of problem: A task |
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needs an external library and it has a nested classpath |
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element so that you can point it to this external library, but |
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that doesn't work unless you put the external library into the |
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<code>CLASSPATH</code>.</p> |
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<p>The root of the problem is that the class that needs the |
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external library is on the <code>CLASSPATH</code>.</p> |
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<p>When you specify a nested <code><classpath></code> in |
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Ant, Ant creates a new class loader that uses the path you |
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have specified. It then tries to load additional classes from |
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this classloader.</p> |
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<p>In most cases - for example the two cases above - Ant |
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doesn't load the external library directly, it is the loaded |
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class that does so.</p> |
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<p>In the case of <code><junit></code> it is the task |
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implementation itself and in the case of |
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<code><style></code> it is the implementation of the |
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<code>org.apache.tools.ant.taskdefs.XSLTLiaison</code> |
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class.</p> |
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<p>Ant's class loader implementation uses Java's |
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delegation model, see <a href="http://java.sun.com/products/jdk/1.2/docs/api/java/lang/ClassLoader.html">http://java.sun.com/products/jdk/1.2/docs/api/java/lang/ClassLoader.html</a> |
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the paragraph</p> |
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<blockquote>The <code>ClassLoader</code> class uses a |
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delegation model to search for classes and resources. Each |
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instance of <code>ClassLoader</code> has an associated parent |
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class loader. When called upon to find a class or resource, a |
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<code>ClassLoader</code> instance will delegate the search for |
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the class or resource to its parent class loader before |
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attempting to find the class or resource itself. The virtual |
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machine's built-in class loader, called the bootstrap |
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class loader, does not itself have a parent but may serve as |
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the parent of a <code>ClassLoader</code> |
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instance.</blockquote> |
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<p>This means, Ant's class loader will consult the |
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bootstrap class loader first, which tries to load classes from |
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<code>CLASSPATH</code>. The bootstrap class loader |
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doesn't know anything about Ant's class loader or |
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even the path you have specified.</p> |
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<p>If the bootstrap class loader can load the class Ant has |
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asked it to load, this class will try to load the external |
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library from <code>CLASSPATH</code> as well - it doesn't |
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know anything else - and will not find it unless the library |
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is in <code>CLASSPATH</code> as well.</p> |
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<p>To solve this, you have two major options:</p> |
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<ol> |
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<li>put all external libaries you need in |
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<code>CLASSPATH</code> as well this is not what you want, |
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otherwise you wouldn't have found this FAQ entry.</li> |
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<li>remove the class that loads the external library from |
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the <code>CLASSPATH</code>.</li> |
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</ol> |
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<p>The easiest way to do this is to remove |
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<code>optional.jar</code> from <code>ANT_HOME/lib</code>. If |
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you do so, you will have to <code><taskdef></code> all |
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optional tasks and use nested <code><classpath></code> |
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elements in the <code><taskdef></code> tasks that point |
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to the new location of <code>optional.jar</code>. Also, |
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don't forget to add the new location of |
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<code>optional.jar</code> to the |
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<code><classpath></code> of your |
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<code><style></code> or <code><junit></code> |
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task.</p> |
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<p>If you want to avoid to <code><taskdef></code> all |
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optional tasks you need, the only other option is to remove |
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the classes that should not be loaded via the bootstrap class |
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loader from <code>optional.jar</code> and put them into a |
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separate archive. Add this separate archive to the |
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<code><classpath></code> of your |
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<code><style></code> or <code><junit></code> task |
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- and make sure the separate archive is not in |
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<code>CLASSPATH</code>.</p> |
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<p>In the case of <code><junit></code> you'd have |
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to remove all classes that are in the |
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<code>org/apache/tools/ant/taskdefs/optional/junit</code> |
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directory, in the <code><style></code> case it is one of |
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the <code>*Liaison</code> classes in |
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<code>org/apache/tools/ant/taskdefs/optional</code>.</p> |
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<p>If you use the option to break up <code>optional.jar</code> |
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for <code><junit></code>, you still have to use a |
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<code><taskdef></code> with a nested |
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<code><classpath></code> to define the junit task.</p> |
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</blockquote> |
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</td></tr> |
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</table> |
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</a> |
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</blockquote> |
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</td></tr> |
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Stefan Bodewig