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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>·</code> ([http://www.fileformat.info/info/unicode/char/b7/index.htm &#xB7;], a valid character in XQuery names, but not in Java) can be used to append exact Java parameter types to the function name. Class types must be referenced by their full path.
The [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/QueryResource.java QueryResource] interface can be implemented to enforce finalizing operations, such as the closing of opened connections or resources in a module. Its {{Code|close()}} method will be called after a query has been fully evaluated.
→URI Rewriting
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_RewritingURI Rewriting|URI Rewriting]] steps are applied to the URI.
# Slashes in the resulting URI are replaced with dots.
# The last path segment of the URI is capitalized and rewritten to [https://en.wikipedia.org/wiki/CamelCase camel caseCamelCase].
The normalization steps are skipped if the URI is prefixed with {{Code|java:}}. See the following examples:
==Functions and Variables==
{| class="wikitable"
| 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 must be are converted to equivalent Java typesvalues, and the result must be of a Java function is converted back to an XQuery types. A table with all mappings is listed value (see [[#Data Types|at the endData Types]] of this article).
If a Java function is not found, it XQuery values may help need to explicitly be cast your XQuery valuesthe 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=
=Module Imports=
An alternative solution is to access Java code can also be integrated by ''importing'' classes as modules. A new instance of the addressed class is will be created, which can then be accessed referenced in the query body.
The following, (side-effecting ) example returns the number of distinct values added to a hash set (the . The boolean values returned by {{Code|set:add()}} will be swallowed):
<pre class="brush:xquery">
import module namespace set = "java:java.util.HashSet";
prof:void(
for $s in ("one", "two", "one")
</pre>
The advantages of this approach is that the execution of imported code classes is executed faster more efficient than the execution of instances that are 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 fails if the addressed class provides a has no default constructor, but at least one constructor with no arguments.
=Context-AwarenessIntegration=
Java classes can be coupled even more closely to the BaseX core library.If a class inherits the abstract [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/QueryModule.java QueryModule] class, the two variables [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/QueryContext.java queryContext] and [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/StaticContext.java staticContext] get available, which provide access to the global and static context of a query. Additionally The [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/QueryResource.java QueryResource] interface can be implemented to enforce finalizing operations, such as the default closing of opened connections or resources in a module. Its {{Code|close()}} method will be called after a query has been fully evaluated. ==Annotations== The internal properties of functions can be changed assigned via annotations:
* Java functions can only be executed by users with [[User_Management|Admin permissions]]. You may annotate a function with {{Code|@Requires(<Permission>)}} to also make it accessible to users with less privileges.
* Java code is treated as ''context-independent''. If a function accesses the query context, it should be annotated as {{Code|@ContextDependent}}
* Java code is treated as ''focus-independent''. If a function accesses the current context item, position or size, it should be annotated as {{Code|@FocusDependent}}
The following XQuery code invokes two Java methods. The first Java function retrieves information from the static query context, and the second one throws a query exception:
[http://www.w3.org/TR/xpath-functions-30/#properties-of-functions function properties].
==Locking==
By default, a Java function will be executed in parallel with other code. However, if a Java function performs sensitive write operations, it is advisable to explicitly lock the code. This can be realized via locking annotations:
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:
| <code>null</code>
|}
==URI Rewriting==
Before a Java class or module is accessed, its namespace URI will be normalized:
# If the URI is a URL:
## colons will be replaced with slashes,
## in the URI authority, the order of all substrings separated by dots is reversed, and
## dots in the authority and the path are replaced by slashes. If no path exists, a single slash is appended.
# Otherwise, if the URI is a URN, colons will be replaced with slashes.
# Characters other than letters, dots and slashes will be replaced with dashes.
# If the resulting string ends with a slash, the {{Code|index}} string is appended.
If the resulting path has no file suffix, it may point to either an XQuery module or a Java archive.
The following examples show some rewritings:
* {{Code|<nowiki>http://basex.org/modules/hello/World</nowiki>}} → {{Code|org/basex/modules/hello/World}}
* {{Code|<nowiki>http://www.example.com</nowiki>}} → {{Code|com/example/www/index}}
* {{Code|a/little/example}} → {{Code|a/little/example}}
* {{Code|a:b:c}} → {{Code|a/b/c}}
=Changelog=
; Version 8.4
* UpdatesUpdated: Rewriting rules ;Version 8.2 * Added: [[#URI Rewriting|URI Rewriting]]: support for URNs
; Version 8.0
* Added: import of Java modules, context awareness
* Added: [[Category:XQuery#Packaging|Packaging]], [[Category:API#URI Rewriting|URI Rewriting]]
