Writing extension functions in Java
Extension functions may be implemented in Java.
Java extension functions can also be used when you are running on the
.NET platform, provided the class implementing the function is a standard class in the GNU Classpath
library (which covers nearly all the classes defined in the JDK). In other cases,
you should compile the Java code into a .NET assembly using the IKVMC compiler, in which case it behaves in the same way as
an extension function written in any other .NET language and compiled into CIL:
see Writing extension functions under .NET
An extension function is invoked using a name such as
The prefix must be the prefix associated with a namespace declaration that is in scope.
The namespace URI is used to identify a Java class, and the local name is used to identify
a method, field, or constructor within the class.
The command line option -TJ is useful for debugging the loading of Java
extensions. It gives detailed information about the methods that are examined for
a possible match.
There are various ways a mapping from URIs to Java classes can be established.
The simplest is to use a URI that identifies the Java class explicitly.
The namespace URI should be "java:" followed by the fully-qualified class name
The class must be on the classpath.
For compatibility with other products and previous Saxon releases, Saxon also supports
certain other formats of URI. The URI may be a string containing a "/",
in which the fully-qualified class name appears after the final "/".
xmlns:date="http://www.jclark.com/xt/java/java.util.Date"). The part of
the URI before the final "/" is immaterial.
xmlns:date="java.util.Date" is also supported.
The Saxon namespace URI
http://saxon.sf.net/ is recognised as a special case. In most cases it causes the
function to be loaded from the class
net.sf.saxon.functions.Extensions but in a few cases,
saxon:evaluate, the function is recognized by the compiler as if it were a built-in function.
The various EXSLT namespaces are also recognized specially.
In XSLT it is also possible to set up a mapping from a URI to a Java class using a
declaration in the stylesheet. This declaration can also name a Java archive, which means the class does not
have to be on the classpath. The
saxon:script mechanism is not widely used and may be
withdrawn in a future release.
The rest of this section considers how a Java method, field, or constructor is identified. This decision
(called binding) is always made at the time the XPath expression is compiled. (In previous Saxon releases
it was sometimes delayed until the actual argument values were known at run-time).
There are three cases to consider: static methods, constructors, and instance-level methods. In
addition, a public field in a class is treated as if it were a zero-argument method, so public static
fields can be accessed in the same way as public static methods, and public instance-level fields
in the same way as instance-level methods.