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{{Mark|Updated with Version 8.4}}: A Java class is identified by a namespace URI. The original URI is rewritten as follows:
A Java variable is retrieved, functions and variables can be referenced and a Java function is invoked, evaluated by a usual the existing XQuery function call. syntax: * The namespace of its QName the function name identifies the Java class, and the .* The local partof the name, which is rewritten to camel case, identifies a variable or function of that class.* The middle dot character (<code>[http://www.fileformat.info/info/unicode/char/b7/index.htm ·/&#xB7;]</code>) is a valid character in XQuery names, but not in Java. It can be used to append exact Java parameter types to the function name. Class types must be referenced by their full path.
[[Category:XQuery]]
[[Category:API]]
no edit summary
The Java Binding feature is an extensibility mechanism which enables developers
to directly access Java variables and execute code from XQuery. Addressed Java code must either be contained in the Java classpath, or it must be located in the [[Repository]].
Please bear in mind that the execution of Java code may cause side effects that conflict with the functional nature of XQuery, or may introduce new security risks to your project.
=Identification=
==Classes==
# The [[Repository#URI_Rewriting|URI Rewriting]] steps are applied to the URI.
==Functions and Variables==
{| class="wikitable sortable" width="100%"
|- valign="top"
! Type
|- valign="top"
| Variable
| <code>Q{java.lang.Integer}MIN_VALUE()</code>| <code>[https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html#MAX_VALUE Integer.MIN_VALUE]</code>
|- valign="top"
| Function
| <code>Q{java.lang.Object}hash-code()</code>
| <code>[https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#hashCode()object.hashCode()]</code>|- valign="top"| Function with types| <code>Q{java.lang.String}split·java.lang.String·int(';', 3)</code>| <code>[https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#split-java.lang.String-int- string.split(";", 3)]</code>
|}
As XQuery and Java have different type systems, XQuery arguments are converted to equivalent Java values, and the result of a Java function is converted back to an XQuery value (see [[#Data Types|Data Types]]).
If a Java function is not found, XQuery values may need to be cast the target type. For example, if a Java function expects a primitive {{Code|int}} value, you will need to convert your XQuery integers to {{Code|xs:int}}.
=Namespace Declarations=
</pre>
The constructor of a class can be invoked by calling the virtual function {{Code|new()}}. Instance methods can then called by passing on the resulting Java object as first argument. In the following example, 256 bytes are written to the file {{Code|output.txt}}. First, a new {{Code|FileWriter}} instance is created, and its {{Code|write()}} function is called in the next step:
<pre class="brush:xquery">declare namespace fw = "java.io.FileWriter";
</pre>
The advantages of this approach is that imported code is executed faster than instances created at runtime via {{Code|new()}}. A drawback is that no arguments can be passed on to the class constructor. As a consequence, the import only works will fail if the class provides a has at least one constructor with arguments and no argumentsdefault constructor.
=Context-Awareness=
If an XQuery expression is run which calls the Java {{Code|write()}} function, every other query that calls {{Code|write()}} or {{Code|read()}} needs to wait for the query to be finished. If a query calls the {{Code|read()}} function, only those queries are queued that call {{Code|write()}}, because this function is only annotated with a {{Code|read}} lock. More details on parallel query execution can be found in the article on [[Transaction Management]].
=Data Types=
The following table lists the mappings of XQuery and Java types:
{| class="wikitable"
|- valign="top"
! XQuery Type
! Java Type
|- valign="top"
| <code>xs:string</code>
| <code>String</code>, <code>char</code>, <code>Character</code>
|- valign="top"
| <code>xs:boolean</code>
| <code>boolean</code>, <code>Boolean</code>
|- valign="top"
| <code>xs:byte</code>
| <code>byte</code>, <code>Byte</code>
|- valign="top"
| <code>xs:short</code>
| <code>short</code>, <code>Short</code>
|- valign="top"
| <code>xs:int</code>
| <code>int</code>, <code>Integer</code>
|- valign="top"
| <code>xs:long</code>
| <code>long</code>, <code>Long</code>
|- valign="top"
| <code>xs:float</code>
| <code>float</code>, <code>Float</code>
|- valign="top"
| <code>xs:double</code>
| <code>double</code>, <code>Double</code>
|- valign="top"
| <code>xs:decimal</code>
| <code>java.math.BigDecimal</code>
|- valign="top"
| <code>xs:integer</code>
| <code>java.math.BigInteger</code>
|- valign="top"
| <code>xs:QName</code>
| <code>javax.xml.namespace.QName</code>
|- valign="top"
| <code>xs:anyURI</code>
| <code>java.net.URI</code>, <code>java.net.URL</code>
|- valign="top"
| ''empty sequence''
| <code>null</code>
|}
=Changelog=
; Version 8.4
* UpdatesUpdated: Rewriting rules
; Version 8.0
* Added: import of Java modules, context awareness
