10 Developing and Deploying Custom XPath Functions

10.1 Implementing a Function in Java as a Java XPath Class

Since the custom function can be invoked either as an XPath or XSL function, the implementation class must take care of both. For this reason, the hosting class must have at least:

• A public static method with the same name as the function name.

  This method is used by the XSL function invocation. Currently, optional parameters on custom functions are not supported when registering with JDeveloper. For this reason, it is recommended to avoid functions with optional parameters.

• A public static inner class which implements:

  oracle.fabric.common.xml.xpath.IXPathFunction

  This interface has the method:

  Object call (IXPathContext context, List args) throws XPathFunctionException that gets called by service engines when the XPath function is invoked. When the function is called, the runtime engine passes the XPathContext and list of arguments passed to the function. IXPathContext enables you to get access to the BPEL variable values within the execution context. The implementation of this method should naturally delegate to the public static method representing the function.

  Here is a custom function implementation to get the current date. The implementation takes care of supporting both XSL and XPath. The function also has an optional parameter to show how overloaded methods are implemented:

  Example 10-1 Custom Function Implementation to Get the Current Date

  package oracle.apps.aia.core;•
  import java.text.SimpleDateFormat; 
  import java.util.Date; import 
  java.util.List;
  import oracle.fabric.common.xml.xpath.IXPathContext;
  import oracle.fabric.common.xml.xpath.IXPathFunction;
  import oracle.fabric.common.xml.xpath.XPathFunctionException;
  public class DateUtils
  {
  public static class GetCurrentDateFunction implements IXPathFunction
  {
  public Object call(IXPathContext context, List args) 
  throws XPathFunctionException
  {
  if (args.size() == 1)
  {
  String mask = (String) args.get(0); 
  if(mask==null || mask.equals(""))
  mask = "yyyy-MM-dd"; 
  return getCurrentDate(mask);
  }
  throw new XPathFunctionException("must pass one argument.");
  }
  }
  public static String getCurrentDate(String formatMask)
  {
  SimpleDateFormat df = new SimpleDateFormat(formatMask) 
  String s = df. format (new Date()); 
  return s;
  }
  . . .
  }
  

10.2 Deploying the XPath/XSL Function in JDeveloper

Custom functions should be registered in JDeveloper to be able to show them with BPEL expression builder and in the XSL Mapper. To do that, provide a User Defined Extension Functions config file [ext-soa-xpath-functions-config.xml] and register it with JDeveloper through FilePreferencesXSL Map.

This config file looks like:

<?xml version="1.0" encoding="UTF-8"?>
<soa-xpath-functions xmlns=http://xmlns.oracle.com/soa/config/xpath xmlns:utl="http://www.oracle.com/XSL/Transform/java/oracle.apps.aia.core.DateUtils"
<function name="utl:getCurrentDate">
 <className>oracle.xpath.CustomFunction</className>
 <return type="string"/>
 <params>
  <param name="formatMask" type="string"/> 
 <params>
</function> 
<function ...>
 . . .
</function> 
</functions>

The implementation classes must be zipped/jared and dropped at:. $SOA_HOME/soa/modules/oracle.soa.ext_11.x.x/classes folder. This way, these classes will be placed in the classpath of WebLogic server.

10.3 Deploying the XPath/XSL Function in the Application Server

The Java XPath function should be registered with the application server. This is done by adding an entry in the ext-soa-xpath-functions-config.xml file, which is found at: $SOA_HOME/soa/modules/oracle.soa.ext_11.x.x/classes\META-INF. This file contains the list and descriptions of all XPath functions defined in the system.

Each function entry in this file has this information:

• <function>: Has the name attribute that defines XPath function name.

• <classname>: Defines the XPath implementation class name. In this case, it is the inner class name.

• <return>: Used to define return type.

• <params>:

  • All the parameters required by the function.

  • <param name="formatMask" type="string"/>

  • For each of the parameter passed specify the name and the data type of the input.

<function name="utl:getCurrentDate">
 <className>oracle.xpath.CustomFunction</className>
 <return type="string"/>
 <params>
  <param name="formatMask" type="string"/> 
 <params>
</function> 

The implementation classes must be dropped at: $SOA_HOME/soa/modules/oracle.soa.ext_11.x.x/classes folder. This way, these classes will be placed in the classpath of the SOA container and available to the classloader.