Java Bindings

This article is part of the Query Portal. It demonstrates how Java code can be invoked from XQuery.

The Java Binding query feature is an extensibility mechanism which enables developers to directly access Java variables and execute code from XQuery. Java classes are identified by namespaces; the namespace URI must be of the form java:fully.qualified.ClassName.

The following example uses Java’s Math class and returns the cosine of an angle. The cos() method can be directly called, as it is a static method:

declare namespace math = "java:java.lang.Math";
math:cos(xs:double(0))

The next example writes 256 bytes to the file output.txt. First, a new FileWriter instance is created: by calling the new() function, the class constructor is invoked. Instance methods are called by passing on the resulting Java object as first argument:

declare namespace fw = "java:java.io.FileWriter";
 let $file := fw:new('output.txt')
return (
  for $i in 0 to 255
  return fw:write($file, xs:int($i)),
  fw:close($file)
)

In general, it is recommended to use XQuery expressions and functions whenever possible, as Java code cannot be pre-compiled, and will often be evaluated slower than optimized XQuery code. Next, Java code can only be executed with admin permissions.