How can I declare “unknown handlers” in Struts 2?

Question

I have been working a lot on how to solve error 404 and NoSuchMethodException in Java Enterprise with Spring and Struts2 Yesterday I read that unknownhandlers can help me to solve those issues.

I have put this into my struts.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>
  <bean name="unknownhandler" type="com.opensymphony.xwork2.UnknownHandler" class="UnknownActionHandler"/>

  <unknown-handler-stack>
    <unknown-handler-ref name="unknownhandler"/>
    <!--<unknown-handler-ref name="error" />-->
  </unknown-handler-stack>

  <constant name="struts.ui.theme" value="simple"/>
  <constant name="struts.objectFactory.spring.autoWire" value="name"/>
  <constant name="struts.locale" value="es_MX" />
  <constant name="struts.i18n.encoding" value="UTF-8" />    
  <constant name="struts.custom.i18n.resources" value="org.aporta.model.resources.etiquetas, org.aporta.bss.resources.CodesBss"/> 
  <constant name="struts.devMode" value="true" />
  <constant name="struts.configuration.xml.reload" value="true"/>
  <constant name="struts.enable.DynamicMethodInvocation" value="true" />

  ...more code

</struts>

When I run the project I get this error:

org.xml.sax.SAXParseException; systemId: file:/home/paulfelix/Documents/workingit/portal/src/java/portal.xml; lineNumber: 33; columnNumber: 26; Element type "unknown-handler-stack" must be declared.
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:198)
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:134)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:437)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:368)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:325)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleStartElement(XMLDTDValidator.java:1906)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.startElement(XMLDTDValidator.java:742)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:378)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2770)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:117)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1213)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(SAXParserImpl.java:649)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl.parse(SAXParserImpl.java:333)
at com.opensymphony.xwork2.util.DomHelper.parse(DomHelper.java:117)

...more code below.

Where can I declare the unknown handler stack?

Can anyone give me an clear example how to implement unknownhandlers?

Answer 1

The DTD is usually your friend; knowing how to read it can save a lot of time:

<!ELEMENT struts ((package|include|bean|constant)*, unknown-handler-stack?)>

Ie, at the end of the config file.

Note that they're only available from ~2.1 onwards.