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This article is part of the [[XQuery|XQuery Portal]].It demonstrates two different ways to invoke Java code from XQuery, and an extension it presents extensions to make Java code aware of access the current query contextfrom Java.

to directly access Java variables and execute code from XQuery. Addressed Java classes are identified bynamespaces. The namespace URI code must simply contain either be contained in the fully qualified class name.The URI can optionally Java classpath, or it must be prefixed with located in the string {{Code|java:}} to enforce thatthe addressed code is written in Java[[Repository]].

If Please bear in mind that the addressed 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== A Java class is not found identified by a namespace URI. The original URI is rewritten as follows: # The [[Repository#URI_Rewriting|URI Rewriting]] steps are applied to the URI.# Slashes in the classpathresulting URI are replaced with dots.# The last path segment of the URI is capitalized and rewritten to [https://en.wikipedia.org/wiki/CamelCase camel case]. The normalization steps are skipped if the URI is prefixed with {{Code|java:}}. See the following examples: * <code><nowiki>http://basex.org/modules/meta-data</nowiki></code> → <code>org.basex.modules.MetaData</code>* <code>java:java.lang.String</code> → <code>java.lang.String</code> ==Functions and Variables== Java functions and variables can be referenced and evaluated by the existing XQuery function syntax: * The namespace of the function name identifies the Java class.* The local part of the name, it first needs 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 &amp;#xB7;], a valid character in XQuery names, but not in Java) can beused to append exact Java parameter types to the function name. Class types must be referenced by their full path. installed in {| class="wikitable"|- valign="top"! Type! XQuery! Java|- 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 [[Repository#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}}.

Java classes can be declared via namespaces. The namespace can then be used tocall static functions contained in that class. Variables are represented asfunction with 0 parameters. The In the following example uses , Java’s {{Code|Math}} class to return is referenced. When executed, the query returns the cosine of an angleby calling the static method {{Code|cos()}}, and the value of π by addressing the staticvariable via {{Code|PI()}}:

The new With the [[XQuery 3.0#Expanded QNames|Expanded QName]] notation of XQuery 3.0,the namespace can directly be applied as well to directly specify a namespace URI instead of embedded in the prefixfunction call:

The constructor of a class can be invoked by calling the virtualfunction {{Code|new()}}. Instance methods can then called bypassing 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. The {{Code|java:}} prefix is omitted inthe URI:

Function names with dashes will be rewritten to Java’s camel case notation: <pre class="brush:xquery">XQuery: get-contents($x as xs:string) If the result of a Java : getContents(String x)</pre> Strings with call contains invalid XML characters , it will be rejected by default. The validity check can be disabled by setting the [[Options#CHECKSTRINGS|CHECKSTRINGS]] option to false. The following query writes a file with a single 00-byte, which will then be successfully read via Java functions:

Note that Java code cannot be pre-compiled, and will often as such be evaluated slower than optimizedXQuery code.

Java code can also be integrated accessed 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.

An The following (side-effecting) example (returns the number of distinct values added to a hash set. The boolean values returned by {{Code|set:add()}} are ignored)will be swallowed:

import module namespace set = "java:java.util.HashSet";let $loop prof:=void( for $i s in 1 to 10000("one", "two", "one") return set:add($is)return ),set:size()

Advantages The advantages of this approach are:* is the execution of imported code can be executed faster classes is more efficient than the execution of instances that are created at runtime via {{Code|new()}}.* the work on class instances ensures that queries run in parallel will not cause any concurrency issues (provided that the class contains no static variables or functions). A drawback is that no arguments can be passed on to the class constructor.As a consequence, the import fails if the addressed class must provide a has no default constructor, but at least one constructor with no arguments.

{{Mark|Updated with Version 7.8}}: {{Code|context}} variable has been split into {{Code|queryContext}} and {{Code|staticContext}}. 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 default properties of functions can be changed via annotations:

* This example is inherited from inherits the {@link QueryModule} classand * implements the QueryResource interface.

public class ContextModule extends QueryModule implements QueryResource {