java.lang.reflect.InvocationTargetException in jetty-web.xml when setting WebAppContext.configurationClasses

I'm trying to add org.eclipse.jetty.annotations.AnnotationConfiguration to the configurationClasses property of org.eclipse.jetty.webapp.WebAppContext but (when invoking Jetty with sbt containe:start), getting:

[warn] Config error at <Set name="configurationClasses">
[warn]         <Array type="java.lang.String"><Item>org.eclipse.jetty.webapp.WebInfConfiguration</Item><Item>org.eclipse.jetty.webapp.WebXmlConfiguration</Item><Item>org.eclipse.jetty.webapp.MetaInfConfiguration</Item><Item>org.eclipse.jetty.webapp.FragmentConfiguration</Item><Item>org.eclipse.jetty.plus.webapp.EnvConfiguration</Item><Item>org.eclipse.jetty.plus.webapp.PlusConfiguration</Item><Item>org.eclipse.jetty.annotations.AnnotationConfiguration</Item><Item>org.eclipse.jetty.webapp.JettyWebXmlConfiguration</Item></Array>
[warn]     </Set>java.lang.reflect.InvocationTargetException in file:/Users/erik.allik/code/scala/webtest/src/main/webapp/WEB-INF/jetty-web.xml
[warn] Failed startup of context o.e.j.w.WebAppContext@33acb4a1{/,[file:/Users/erik.allik/code/scala/webtest/src/main/webapp/],STARTING}

I've tried changing the <Set ...> to a <Call name="setConfigurationClasses"> (with both the String[] as well as List<String> variants) to no avail—still getting the same reflection exception every time.

My jetty-web.xml is as follows:

<?xml version="1.0"  encoding="ISO-8859-1"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">
<Configure class="org.eclipse.jetty.webapp.WebAppContext">
    <Set name="configurationClasses">
        <Array type="java.lang.String">
            <Item>org.eclipse.jetty.webapp.WebInfConfiguration</Item>
            <Item>org.eclipse.jetty.webapp.WebXmlConfiguration</Item>
            <Item>org.eclipse.jetty.webapp.MetaInfConfiguration</Item>
            <Item>org.eclipse.jetty.webapp.FragmentConfiguration</Item>
            <Item>org.eclipse.jetty.plus.webapp.EnvConfiguration</Item>
            <Item>org.eclipse.jetty.plus.webapp.PlusConfiguration</Item>
            <Item>org.eclipse.jetty.annotations.AnnotationConfiguration</Item>
            <Item>org.eclipse.jetty.webapp.JettyWebXmlConfiguration</Item>
        </Array>
    </Set>
</Configure>

ANSWER: deciding by https://github.com/JamesEarlDouglas/xsbt-web-plugin/blob/master/src/jetty-9/scala/Jetty9Runner.scala, xsbt-web-plugin sets the configurations property of WebAppContext to a hardcoded value, so no matter what's in the XML configs, it probably simply gets ignored (or causes an error, apparently).

Solution

The Configuration classes exist to configure the WebAppContext itself.

Adding the Configurations in the jetty-web.xml or the Jetty IoC XML Context Deployable is too late in the lifecycle.

If you look at etc/jetty-annotations.xml you'll see ...

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure_9_0.dtd">

<Configure id="Server" class="org.eclipse.jetty.server.Server">
  <!-- =========================================================== -->
  <!-- Add annotation Configuring classes to all webapps for this Server -->
  <!-- =========================================================== -->
  <Call class="org.eclipse.jetty.webapp.Configuration$ClassList" name="setServerDefault">
    <Arg><Ref refid="Server" /></Arg>
    <Call name="addBefore">
      <Arg name="beforeClass">org.eclipse.jetty.webapp.JettyWebXmlConfiguration</Arg>
      <Arg>
        <Array type="String">
          <Item>org.eclipse.jetty.annotations.AnnotationConfiguration</Item>
        </Array>
      </Arg>
    </Call>
  </Call>
</Configure>

and etc/jetty-plus.xml you'll see ...

<?xml version="1.0"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure_9_0.dtd">

<!-- =============================================================== -->
<!-- Configure extended support for webapps                          -->
<!-- =============================================================== -->
<Configure id="Server" class="org.eclipse.jetty.server.Server">

  <!-- =========================================================== -->
  <!-- Add plus Configuring classes to all webapps for this Server -->
  <!-- =========================================================== -->
  <Call class="org.eclipse.jetty.webapp.Configuration$ClassList" name="setServerDefault">
    <Arg><Ref refid="Server" /></Arg>
    <Call name="addAfter">
      <Arg name="afterClass">org.eclipse.jetty.webapp.FragmentConfiguration</Arg>
      <Arg>
        <Array type="String">
          <Item>org.eclipse.jetty.plus.webapp.EnvConfiguration</Item>
          <Item>org.eclipse.jetty.plus.webapp.PlusConfiguration</Item>
        </Array>
      </Arg>
    </Call>
  </Call>
</Configure>

If you notice, you'll see that these are configured at the server level, and are based on existing defaults (to satisfy ordering requirements of the Configurations).