Bureaucrats, editor, reviewer, Administrators
13,550
edits
Changes
Jump to navigation
Jump to search
{{Mark|Updated with Version 8.4}}:
Both Java functions and variables and Java function are can be referenced and evaluated by usual the existing XQuery function callssyntax:
The following, In the (side-effecting ) example returns below, the number size of distinct values added to a Java hash set (the is returned. The boolean values that are returned by {{Code|set:add()}} will be are swallowed):
=ContextJava 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-Awareness=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.
Java classes can be coupled more closely to the BaseX core library.If a class inherits the abstract The [https://github.com/BaseXdb/basex/blob/master/basex-core/src/main/java/org/basex/query/QueryModuleQueryResource.java QueryModuleQueryResource] classinterface can be implemented to enforce finalizing operations, such as 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 closing of opened connections or resources in a querymodule. Additionally, Its {{Code|close()}} method will be called after the default XQuery expression has been fully evaluated. ==Annotations== The internal properties of functions can be changed assigned via annotations:
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 In the closing of opened connections or resources in a module. Its {{Code|close()}} method will be called after a query has been fully evaluated. The following XQuery code invokes two Java methods. The first Java function retrieves , information from the static query contextis returned by the first function, and the second one throws a query exceptionis raised by the second function:
The following table lists the mappings of XQuery and Java typesare mapped as follows:
→Functions and Variables
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==
A Java class is identified by a namespace URI. The original URI is rewritten as follows:
# 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:
* <code><nowiki>http://basex.org/modules/meta-data</nowiki></code> → <code>org.basex.modules.MetaData</code>
==Functions and Variables==
* 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 (<code>[http://www.fileformat.info/info/unicode/char/b7/index.htm ·]</code> (&#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.
{| class="wikitable"
|- valign="top"
| Variable
| <code>Q{java.lang.Integer}MIN_VALUE#0()</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#0($object)</code>| <code>[https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#hashCode() Object#object.hashCode()]</code>
|- valign="top"
| Function with types
| <code>Q{java.lang.String}split·java.lang.String·int#2($string, ';', xs:int(3))</code>| <code>[https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#split-java.lang.String-int- String#string.split(";", 3)]</code>
|}
</pre>
If the result of a Java call contains invalid XML characters, it will be rejected. The validity check can be disabled by setting the [[Options#CHECKSTRINGS|CHECKSTRINGS]] option to false. The following query writes In the example below, a file with a single {{Code|00-}} byteis written, which and this file will then be successfully read accessed by via Java functions:
<pre class="brush:xquery">
=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.
<pre class="brush:xquery">
import module namespace set = "java:java.util.HashSet";
prof:void(
for $s in ("one", "two", "one")
</pre>
The advantages execution of this approach is that 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. =Integration=
* 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 ''focus-independent''. If a function accesses the current context item, position or size, it should be annotated as {{Code|@FocusDependent}}
<pre class="brush:xquery">
context:user()
},
try { element to-int { try { context:to-int('abc') }} catch basex:error { catch * element error { 'Error in line', $err:line-number description }
}
</pre>
/**
* Returns the name of the logged in user.
* @return userstring
*/
@Requires(Permission.NONE)
/**
* Converts the specified string to an integer.
* @param value string representationto be converted * @return resulting integer
* @throws QueryException query exception
*/
return Integer.parseInt(value);
} catch(NumberFormatException ex) {
throw new QueryException(ex.getMessage()"Integer conversion failed: " + value);
}
}
@Override
public void close() {
// see description abovedefined in QueryResource interface, will be called after query evaluation
}
}
<pre class="brush:xml">
<user>admin</admin>
<to-interror>Error in line 6Integer conversion failed: abc</to-interror>
</pre>
[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==
{| class="wikitable"
| <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:
* {{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: [[#Packaging|Packaging]], [[#URI Rewriting|URI Rewriting]]
