Expresso XML project provides basic facilities for importing and exporting DBObjects to XML format streams and/or files. In addition, a Transaction object has been developed that allows multiple imports and exports via servlets between servers, creating the basis for an XML-based replication. Expresso XML includes and incorporates a copy of the Apache Xerces XML parser and the Apache Xalan XSLT transformation tool.

The configuration files that specify all of the options for Expresso at system startup are in XML format, and these files can be used to specify additional custom properties for your own application. See the "custom-property" element description in the DTD for expresso-config.xml for details. (This DTD can be found in the WEB-INF/classes/com/jcorporate/expresso/core directory.

A controller object called XMLController can import data into any DBObject from an XML format, and export data from the DBObject into an XML format file. This controller is accessed from the "Operations" page in Expresso.

All Controller objects can produce their inputs, outputs and transitions in XML format. This can be used when debugging an application, to examine the elements produced by a particular controller. This XML can also be passed through a specified XSL stylesheet, to produce HTML, WML, PDF, or other XML, as required. This ability is provided by the XMLViewHandler servlet.

Any Controller can be invoked via it's URL with the "style=xml" option. "style=xml" in conjunction with "xsl=none" will produce the XML output directly to the browser. Any other "xsl=..." option will use the specified stylesheet for transformation. If no XSL is defined, the XSL to be used will be determined by the Controller/XSL mappings (defined from the "Setup" page) in the current context.

The use of XSL stylesheets with Controller outputs can be invoked according to a URL parameter, as described above. Furthermore, the configuration file can specify an xsl transformation. That is, instead of specifying a forward for a JSP, a forward can be specified for a .xsl file. For example, considered the action mapping below, from an entry in a fictitious configuration file "myProject-config.xml":

<action path="/MyController" type="com.jcorporate.myproject.controller.MyController" name="default" scope="request" validate="false"> <!-- This method is rendered by a JSP --> <forward name="someMethod" path="/myProject/jsp/register/status.jsp"/> <!-- you can use XSLT transforms here too. any path which ends with .xsl or .xslt will be handled appropriately. --> <forward name="someOtherMethod" path="/myProject/xsl/blah.xsl"/>; </action>

class MyController ... protected void runSomeOtherMethodState(ControllerRequest request, ControllerResponse response) throws ControllerException { ... // set mimetype of result, since xsl is usually translated to html, but // in this case we will be outputting xml request.setParameter("mime", "text/xml"); }

The direction of this project is to adopt a standard XML DTD for representation of Database Objects and making the XML parser 'pluggable' as well as providing XSLT transformation capability (ala Cocoon). Much more is also possible with the XSLT transformations - one goal here is to make a version of the DBMaint servlet with a completely customizable UI via XSL stylesheets.