Converting Wrapped Java Objects
Saxon allows an extension function to return an arbitrary Java object. This will then be wrapped as an XPath item, so that it can be held in a variable and passed subsequently as an argument to another extension function. This second extension function will see the original Java object minus its wrapper, provided it is declared to expect the appropriate Java class.
A wrapped Java object always holds a non-null object value. The Java value null converts to the XPath empty sequence.
A wrapped Java object may be converted to another data type as follows.
It is converted to a string by calling its
It is atomized by calling its
It is converted to a number by converting it first to a string, and then applying the XPath
The effective boolean value of a wrapped Java object (like that of a node) is always true.
The type of a wrapped Java object may be declared in a variable declaration or function
signature using a type name whose namespace URI is
whose local name is the fully qualified name of the Java class, with any "$" signs replaced
by hyphens, and with leading "[" characters replaced by "_-". For example, the
sql:connection extension function returns a value of type
Note that a call on a constructor function (using
prefix:new()) always returns a wrapped
Java object, regardless of the class. But a call on a static method, instance-level method,
or field will return a wrapped Java object only if the result is a class that Saxon does not
specifically recognize as one that it can convert to a regular XPath value. Such classes
List and so on.
In Saxon 9.4 and earlier releases, a wrapped Java object was considered to be an atomic
value (in the XDM type hierarchy, the type representing
java.lang.Object was a
peer of primitive types such as
xs:boolean). In Saxon
9.5, this changed so that wrapped objects are a fourth subtype of
the same level in the type hierarchy as nodes, atomic values, and function items. Atomizing
a wrapped Java object now produces an instance of
xs:string containing the
result of the
toString() method applied to the underlying object.