Changes

==This article is part of the [[XQuery|XQuery Portal]]. It demonstrates different ways to invoke Java Binding==code from XQuery, and it presents extensions to access the current query context from Java.

The Java Binding feature is an extensibility mechanism which allows direct callingenables developersto 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 methods bound code may cause side effects that conflict with the functional nature of XQuery, or may introduce new security risks to your project. {{Mark|Updated with Version 9.6:}}* With the middle dot notation, three adjacent dots can be used to specify array types.* The path to the standard package {{Code|java.lang.}} can now be omitted.* Java objects are now wrapped into function items.* Results of constructor calls are always returned as function item.* A new option {{Option|WRAPJAVA}} was added to control how Java values are converted to XQuery functions .* The Mapping rules were refined and unified. The most important changes:** {{Code|array(*)}} type added.** {{Code|xs:integer}} values are converted to {{Code|long}} values.** {{Code|xs:unsignedShort}} values are converted to {{Code|char}} values.* All error messages were revised and manipulation of wrapped improved. =Identification= ==Classes== A Java objectsclass is identified by a namespace URI.The original URI is rewritten as follows: # The following examples introduce [[#URI Rewriting|URI Rewriting]] steps are applied to the behaviorURI. Please note that # Slashes in the namespace resulting URIare replaced with dots.must be # The last path segment of the form URI is capitalized and rewritten to [https://en.wikipedia.org/wiki/CamelCase CamelCase]. The normalization steps are skipped if the URI is prefixed with {{Code|java:}}. The path to the standard package {{Code|java.lang.}} can be omitted: * <code><nowiki>http://basex.org/modules/meta-data</nowiki></code> → <code>org.basex.modules.MetaData</code>* <code>java:fullyQualifiedClassNamejava.lang.String</code>→ <code>java.lang.String</code>* <code>StringBuilder</code> → <code>java.lang.StringBuilder<blockquote/code>  ==Functions and Variables== Java constructors, 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, which is rewritten to camel case, identifies a variable or function of that class.* The middle dot character <pcode>This example uses [https://www.fileformat.info/info/unicode/char/b7/index.htm ·]</code> (<code>&amp;#xB7;</code>, a valid character in XQuery names, but not in Java) can be used to append exact Java parameter types to the java function name. Class types must be referenced by their full path. Three adjacent dots can be used to address an array argument. {| class="wikitable"|- valign="top"! Addressed code! XQuery! Java|- valign="top"| Variable| <code>Q{Integer}MIN_VALUE()</code>| <code>Integer.MIN_VALUE</code>|- valign="top"| Function| <code>Q{Object}hash-code($object)</code>| <code>object.hashCode()</code>|- valign="top"| Function with argument| <code>Q{String}split·String·int($string, ';', xs:int(3))</code>| <code>string.split(";", 3)</code>|- valign="top"| Constructor with array argument| <code>Q{String}new·byte...(xs:hexBinary('414243'))</code>| <code>Mathnew String(new byte[] { 41, 42, 43 })</code> |} As XQuery and Java have different type systems, XQuery arguments must be 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 the Java function you want to address is not detected, you may need to cast your values to 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= In the following example, the Java {{Code|Math}} class and 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 static variable via {{Code|PI()}}: </psyntaxhighlight lang="xquery"> <pre>declare namespace math = "java:java.lang.Math";math:cos(xs:double(0)), math:PI()</presyntaxhighlight> With the [[XQuery 3.0#Expanded QNames|Expanded QName]] notation of XQuery 3.0, the namespace can directly be embedded in the function call: <syntaxhighlight lang="xquery">Q{java:java.lang.Math}cos(xs:double(0))<p/syntaxhighlight> The next 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 writes , 256 bytes are written to the file <code>{{Code|output.txt</code>}}. First, a new {{Code|FileWriter}} instance is created, and its {{Code|write()}} function is called in the next step: </psyntaxhighlight lang="xquery"> <pre>declare namespace fw = &quot;'java:java.io.FileWriter&quot;';

)</presyntaxhighlight> If the result of a Java call contains invalid XML characters, it will be rejected. The validity check can be disabled by setting {{Option|CHECKSTRINGS}} to false. In the example below, a file with a single {{Code|00}} byte is written, and this file will then be accessed by via Java functions: <syntaxhighlight lang="xquery">declare namespace br = 'java:java.io.BufferedReader';declare namespace fr = 'java:java.io.FileReader'; declare option db:checkstrings 'false'; (: write file :)file:write-binary('00.bin', xs:hexBinary('00')),(: read file :)let $br := br:new(fr:new('00.bin'))return ( br:readLine($br), br:close($br))</syntaxhighlight>  The option can also be specified via a pragma: <syntaxhighlight lang="xquery">(# db:checkstrings #) { br:new(fr:new('00.bin')) ! (br:readLine(.), br:close(.))}</blockquotesyntaxhighlight> =Module Imports=Try/Catch A Java classes can also be instantiated by ''importing'' them as a module: A new instance of the addressed class will be constructed, which can then be referenced in the query body. In the (side-effecting) example below, a HashSet instance is created, values are added, and the size of the set is returned. As {{Code|set:add()}} returns boolean values, {{Function|Profiling|prof:void}} is used to swallow the values: <syntaxhighlight lang="xquery">import module namespace set ="java:java.util.HashSet";prof:void( for $s in ("one", "two", "one") return set:add($s)),set:size()<p/syntaxhighlight> The execution of imported classes is more efficient than the execution of instances that have been created via {{Code|new()}}. In turn, no arguments can be supplied in the import statement, and the construction will only be successful if the class can be instantiated without arguments. =Integration= Java classes can be coupled more closely to BaseX. 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. The well[https://github.com/BaseXdb/basex/blob/master/basex-known trycore/src/main/java/org/basex/query/catch construct QueryResource.java QueryResource] interface can be used implemented to enforce finalizing operations, such as the closing of opened connections or resources in BaseX a module. Its {{Code|close()}} method will be called after the XQuery expression has been fully evaluated. ==Annotations== The internal properties of functions can be assigned via annotations: * Java functions can only be executed by users with [[User_Management|Admin permissions]]. You can annotate a function with {{Code|@Requires(<Permission>)}} to also make it accessible to interceptusers with fewer privileges.run* Java code is treated as ''non-time errorsdeterministic'', as its behavior cannot be predicted by the XQuery processor. This feature You may annotate a function as {{Code|@Deterministic}} if you know that it will have no side effects and will also always yield the same result.* 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 part annotated as {{Code|@FocusDependent}} In the following code, information from the static query context is returned by the first function, and a query exception is raised by the second function: <syntaxhighlight lang="xquery">import module namespace context = 'org.basex.examples.query.ContextModule'; element user { context:user()},try { element to-int { context:to-int('abc') }} catch basex:error { element error { $err:description }}</syntaxhighlight> The imported Java class is shown below: <syntaxhighlight lang="java">package org.basex.examples.query; import org.basex.query.*;import org.basex.query.value.item.*;import org.basex.util.*; /** * This example inherits the {@link QueryModule} class and * implements the QueryResource interface. */public class ContextModule extends QueryModule implements QueryResource { /** * Returns the name of the logged-in user. * @return user string */ @Requires(Permission.NONE) @Deterministic @ContextDependent public String user() { return queryContext.context.user.name; }  /** * Converts the specified string to an integer. * @param value string to be converted * @return resulting integer * @throws QueryException query exception */ @Requires(Permission.NONE) @Deterministic public int toInt(final String value) throws QueryException { try { return Integer.parseInt(value); } catch(NumberFormatException ex) { throw newQueryException("Integer conversion failed: " + value); } }  @Override public void close() { // defined in QueryResource interface, will be called after query evaluation }}<a href/syntaxhighlight> The result will look as follows: <syntaxhighlight lang="httpxml"><user>admin</admin><error>Integer conversion failed: abc</error></syntaxhighlight> Please visit the XQuery 3.0 specification if you want to get more insight into[https://www.w3.org/TR/xqueryxpath-functions-1131/#idproperties-tryof-catchfunctions function properties]. ==Updates== The {{Code|@Updating}} annotation can be applied to mark Java functions that perform write or update operations: <syntaxhighlight lang="java">XQuery 1 @Updating public void backup() { // ...1 Recommendation }</syntaxhighlight> An XQuery expression will be handled as an [[XQuery Update#Updating Expressions|updating expression]] if it calls an updating Java function. In contrast to XQuery update operations, the Java code will immediately be executed, but the result will be cached as if {{Function|Update|update:output}} was called. The annotation is particularly helpful if combined with alock annotation. ==Locking== By default, a Java function will be executed in parallel with other code. If a Java function performs sensitive operations, it is advisable to explicitly lock the code. ===Java Locks=== Java provides a handful of mechanism to control the execution of code. The concurrent execution of functions can be avoided with the {{Code|synchronized}} keyword. For more complex scenarios, the Lock, Semaphore and Atomic classes can be brought into play. ===XQuery Locks=== If you want to synchronize the execution of your code with BaseX locks, you can take advantage of the {{Code|@Lock}} annotation: <syntaxhighlight lang="java"> @Lock("HEAVYIO") public void read() { // ... }  @Updating @Lock("HEAVYIO") public void write() { // ... }<br/syntaxhighlight>  If an XQuery expression invokes {{Code|write()}}, any other query that calls {{Code|write()}} or {{Code|read()}} needs to wait for the query to be finished. The {{Code|read()}} function can be run in parallel; whereas queries will be queued if {{Code|write()}} is called. More details on concurrent querying can be found in the article on [[Transaction Management]]. ==Data Types== ===Conversion to Java=== Before Java code is executed, the arguments are converted to Java values, depending on the addressed function or constructor parameters. The accepted Java types and the original XQuery types are depicted in the second and first column of the table below. ===Conversion to XQuery=== By default, Java values with the most common types (as shown in the second and third column of the table) are converted to XQuery values. All other values are returned as ''Java items'', which are function items with a wrapped Java value. The results of constructor calls are always returned as Java items. The conversion of the wrapped Java value to XQuery is enforced by invoking the function item: Values in {{Code|Iterator}} and {{Code|Iterable}} instances (Lists, Sets and Collections) are converted to items, and maps are converted to XQuery maps: <syntaxhighlight lang="xquery">declare namespace Scanner = 'java:java.util.Scanner';let $scanner := Scanner:new("A B C") => Scanner:useDelimiter(" ")return $scanner()</psyntaxhighlight>  If no conversion is defined, a string is returned, resulting from the {{Code|toString()}} method of the object. This method is also called is the string representation of a Java item is requested: <blockquotesyntaxhighlight lang="xquery"> (: returns the string representations of a HashMap and an ArrayList instance :)'Map: ' || Q{java.util.HashMap}new(),string(Q{java:java.util.ArrayList}new())<p/syntaxhighlight> The conversion can be further controlled with the {{Option|WRAPJAVA}} option. The following values exist: {| class="wikitable"|- valign="top"! Value! Description|- valign="top"| {{Code|some}}| The default: Java values of the most common types are converted, others are wrapped into Java items.|- valign="top"| {{Code|none}}| All Java values are converted. If no conversion is defined, a string is returned, resulting from the {{Code|toString()}} method.|- valign="top"| {{Code|all}}| Java values are wrapped into Java items (excluding those inheriting the internal type {{Code|org.basex.query.value.Value}}).|- valign="top"| {{Code|instance}}| If the method of a class instance was called, the Java value is ignored and the instance is wrapped into a Java item. Otherwise, the Java value is returned.|- valign="top"| {{Code|void}}| Java values are ignored, and an empty sequence is returned instead.|} In the following example, the result of the first function – a char array – is wrapped and passed on to a {{Code|CharBuffer}} function. Without the option, the single-value array would be converted to an {{Code|xs:unsignedShort}} item and the second function call would fail: <bsyntaxhighlight lang="xquery">Example(: Without the pragma, the result of toChars would be converted to an xs:unsignedShort item, and the second function call would fail :</b) (# db:wrapjava all #) { Q{Character}toChars(xs:int(33)) =>Q{java.nio.CharBuffer}wrap()}</psyntaxhighlight>  The next example demonstrates a use case for the {{Code|instance}} option: <presyntaxhighlight lang="xquery">try (: Thanks to the pragma, the function calls can be chained :) declare namespace set = 'java:java.util.HashSet';let $set := (# db:wrapjava instance #) { set:new() => set:add('1 + ') => set:add('2') } catch *return $set()</syntaxhighlight> The {{Code|void}} option is helpful if side-effecting methods return values that do not contribute to the final result: <syntaxhighlight lang="xquery">(: Without the pragma, 100 booleans would be returned by the FLWOR expression :) declare namespace set = 'java:java.util.HashSet';let $set := set:new()return ( (# db:wrapjava void #) { for $i in 1 to 100 return set:add($codeset, $i) }, $descset()) </syntaxhighlight> The irrelevant results could also be swallowed with {{Function|Profiling|prof:void}}. {| class="wikitable"|- valign="top"! XQuery input! Expected or returned Java type! XQuery output|- valign="top"| <code>item()*</code> (no conversion)| <code>org.basex.query.value.Value</code>| <code>item()*</code> (no conversion)|- valign="top"| <code>empty-sequence()</code>| <code>null</code>| <code>empty-sequence()</code>|- valign="top"| <code>xs:string</code>, <code>xs:untypedAtomic</code>| <code>String</code>| <code>xs:string</code>|- valign="top"| <code>xs:unsignedShort</code>| <code>char</code>, <code>Character</code>| <code>xs:unsignedShort</code>|- valign="top"| <code>xs:boolean</code>| <code>boolean</code>, <code>Boolean</code>| <code>xs:boolean</code>|- valign="top"| <code>xs:byte</code>| <code>byte</code>, <code>Byte</code>| <code>xs:byte</code>|- valign="top"| <code>xs:short</code>| <code>short</code>, <code>Short</code>| <code>xs:short</code>|- valign="top"| <code>xs:int</code>| <code>int</code>, <code>Integer</code>| <code>xs:int</code>|- valign="top"| <code>xs:integer</code>, <code>xs:long</code> concat| <code>long</code>, <code>Long</code>| <code>xs:integer</code>|- valign="top"| <code>xs:unsignedLong</code>| <code>java.math.BigInteger</code>| <code>xs:unsignedLong</code> ('Error ['lossy)|- valign="top"| <code>xs:decimal</code>| <code>java.math.BigDecimal</code>| <code>xs:decimal</code>|- valign="top"| <code>xs:float</code>| <code>float</code>, <code>Float</code>| <code>xs:float</code>|- valign="top"| <code>xs:double</code>| <code>double</code>, $<code>Double</code>| <code>xs:double</code>|- valign="top"| <code>xs:QName</code>| <code>javax.xml.namespace.QName</code>| <code>xs:QName</code>|- valign="top"| <code>xs:anyURI</code>| <code>java.net.URI</code>, '<code>java.net.URL</code>| <code>xs:anyURI</code>|- valign="top"| <code>xs:date</code>| <code>javax.xml.datatype.XMLGregorianCalendar</code>| <code>xs:date</code>|- valign="top"| <code>xs:duration</code>| <code>javax.xml.datatype.Duration</code>| <code>xs:duration</code>|- valign="top"| <code>node()</code>| <code>org.w3c.dom.Node</code>| <code>node()</code>|- valign="top"| <code>array(xs:boolean)</code>| <code>boolean[]</code>| <code>xs:boolean*</code>|- valign="top"| <code>array(xs:string)</code>| <code>String[]</code>| <code>xs:string*</code>|- valign="top"| <code>array(xs:unsignedShort)</code>| <code>char[]</code>| <code>xs:unsignedShort*</code>|- valign="top"| <code>array(xs:short)</code>| <code>short[]</code>| <code>xs:short*</code>|- valign="top"| <code>array(xs:int)</code>| <code>int[]</code>| <code>xs: 'int*</code>|- valign="top"| <code>array(xs:integer)</code>, $desc<code>array(xs:long)</code>| <code>long[]</code>| <code>xs:integer*</code>|- valign="top"| <code>array(xs:float)</code>| <code>float[]</code>| <code>xs:float*</code> }|- valign="top"| <code>array(xs:double)</precode> | <code>double[]<p/code>| <bcode>Resultxs:double*</bcode> |- valign="top"| <code>Error Object[XPTY0004]</code> (others)| <code>item()*</code>| <code>array(*)</code> (others)|- valign="top"| <code>map(*)</code>| java.util.HashMap| <code>Wrapped Java object</code>|} ==URI Rewriting== Before a Java class or module is accessed, its namespace URI will be normalized: '+' operator # If the URI is a URL: number expected## 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 foundis appended. If the resulting path has no file suffix, it may point to either an XQuery module or a Java archive: * {{Code|<nowiki>http://basex.org/modules/code>hello/World</pnowiki> }} → {{Code|org/basex/modules/hello/World}}* {{Code|<nowiki>http://www.example.com</blockquotenowiki>}} → {{Code|com/example/www/index}}* {{Code|a/little/example}} → {{Code|a/little/example}}* {{Code|a:b:c}} → {{Code|a/b/c}} =Changelog= ; Version 9.6* Updated: {{Anchor|Data Types}}: {{Code|array(*)}} type added; {{Code|xs:integer}} are converted to {{Code|long}} values. ; Version 9.4* Added: Annotation for [[#Updates|updating functions]].* Updated: Single annotation for read and write locks. ; Version 8.4* Updated: Rewriting rules ;Version 8.2* Added: [[#URI Rewriting|URI Rewriting]]: support for URNs ; Version 8.0* Added: {{Code|QueryResource}} interface, called after a query has been fully evaluated. ; Version 7.8* Added: Java locking annotations* Updated: {{Code|context}} variable has been split into {{Code|queryContext}} and {{Code|staticContext}}. ; Version 7.2.1* Added: import of Java modules, context awareness* Added: [[#Packaging|Packaging]], [[#URI Rewriting|URI Rewriting]]