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See:
Description
| Interface Summary | |
|---|---|
| Declaration | This interface represents the union of global variable declarations and function declarations in XQuery modules |
| UpdateAgent | An UpdateAgent is a callback class that is called to handle a document after it has been updated. |
| XQueryFunctionBinder | XQueryFunctionBinder is an extension of the FunctionLibrary interface used for function libraries that contain user-written XQuery functions. |
| Class Summary | |
|---|---|
| DynamicQueryContext | This object represents a dynamic context for query execution. |
| GlobalVariableDefinition | Class to hold compile-time information about an XQuery global variable or parameter. |
| ImportedFunctionLibrary | This implementation of FunctionLibrary contains all the functions imported into a Query Module. |
| QueryLibrary | A QueryLibrary represents an independently compiled set of query modules that does not include a main module. |
| QueryModule | This class represents a query module, and includes information about the static context of the query module. |
| QueryParser | This class defines extensions to the XPath parser to handle the additional syntax supported in XQuery |
| QueryReader | This class contains static methods used to read a query as a byte stream, infer the encoding if necessary, and return the text of the query as a string; also methods to import functions and variables from one module into another, and check their consistency. |
| QueryResult | This utility class takes the result sequence produced by a query, and wraps it as an XML document. |
| SequenceWrapper | This class can be used in a push pipeline: it accepts any sequence as input, and generates a document in which the items of the sequence are wrapped by elements containing information about the types of the items in the input sequence. |
| StaticQueryContext | StaticQueryContext contains information used to build a StaticContext for use when processing XQuery expressions. |
| UnboundFunctionLibrary | An UnboundFunctionLibrary is not a real function library; rather, it is used to keep track of function calls that cannot yet be bound to a known declared function, but will have to be bound when all user-declared functions are available. |
| UndeclaredVariable | An UndeclaredVariable object is created when a reference is encountered to a variable that has not yet been declared. |
| XQueryExpression | XQueryExpression represents a compiled query. |
| XQueryFunction | A user-defined function in an XQuery module |
| XQueryFunctionLibrary | An XQueryFunctionLibrary is a function library containing all the user-defined functions available for use within a particular XQuery module: that is, the functions declared in that module, and the functions imported from other modules. |
This package provides a relatively low-level API for executing XQuery queries
directly from a Java application. This is no longer the recommended API for writing Java
applications using XQuery: there are two higher-level APIs, s9api (net.sf.saxon.s9api,
and XQJ (javax.xml.xquery. This package also includes internal supporting code
that implements XQuery within Saxon.
For details of the API, see the JavaDoc documentation of individual classes, starting
with the StaticQueryContext.
The first thing you need to do is to create a Configuration object.
This holds values of all the system settings, corresponding to flags available on the command line.
You don't need to set any properties in the Configuration object if you are happy
with the default settings. For schema-aware processing, you will need to create a
EnterpriseConfiguration instead.
Then you need to create a StaticQueryContext object, which you can
do using the newStaticQueryContext() method on the Configuration. As the name
implies, this holds information about the static (compile-time) context for a query. Most aspects
of the static context can be defined in the Query Prolog, but this object allows you to initialize
the static context from the application instead if you need to. Some of the facilities provided are
very much for advanced users only, for example the ability to declare variables and functions, and
the ability to specify a NamePool to be used. One aspect of the static context that you may need
to use is the ability to declare collations. Using the method declareCollation you can
create a mapping between a collation URI (which can then be used anywhere in the Query) and a Java
StringCollator object used to implement that collation.
Having created, and possibly configured, the Configuration and
StaticQueryContext objects, you can now compile a Query using the compileQuery
method on the StaticQueryContext. The text of the
Query can be supplied either as a String or as a Java Reader. There
are thus two different compileQuery methods. Each of them returns the compiled
query in the form of a XQueryExpression. The XQueryExpression, as you would expect,
can be executed repeatedly, as often as you want, in the same or in different threads.
Before you run your query, you may want to build one or more trees representing
XML documents that can be used as input to your query. You don't need to do this: if the query
loads its source documents using the doc() function then this will be done
automatically, but doing it yourself gives you more control. A document node at the root of
a tree is represented in Saxon by the DocumentInfo interface.
The Configuration provides a convenience method, buildDocument(),
that allows an instance of DocumentInfo to be constructed. The input parameter to
this is defined by the class javax.xml.transform.Source, which is part of the
standard Java JAXP API: the Source interface is an umbrella for different kinds of
XML document source, including a StreamSource which parses raw XML from a byte
or character stream, SAXSource which takes the input from a SAX parser (or an
object that is simulating a SAX parser), and DOMSource which provides the input
from a DOM. Saxon-PE also provides wrappers for third-party document models, for example a
DocumentWrapper which allows
the input to be taken from a JDOM document.
To execute your compiled query, you need to create a DynamicQueryContext object
that holds the run-time context information. The main things you can set in the run-time context are:
setParameter()
method. The mappings from Java classes to XQuery/XPath data types is the same as the mapping used for the
returned values from an external Java method call, and is described under
Result of an Extension Function.setContextNode(). For some reason
it isn't possible to set a context item other than a node.You are now ready to evaluate the query. There are several methods on the QueryExpression
object that you can use to achieve this. The evaluate() method returns the result sequence
as a Java java.util.List. The evaluateSingle() method is suitable when you know
that the result sequence will contain a single item: this returns this item as an Object, or returns null
if the result is an empty sequence. There is also an iterator method that returns an iterator
over the results. This is a Saxon object of class net.sf.saxon.SequenceIterator: it is similar
to the standard Java iterator, but not quite identical; for example, it can throw exceptions.
The evaluate() and evaluateSingle() methods return the result as a Java object
of the most appropriate type: for example a String is returned as a java.lang.String, a
boolean as a java.lang.Boolean. A node is returned using the Saxon representation of a node,
net.sf.saxon.om.NodeInfo. With the standard and tinytree models, this object also implements
the DOM Node interface (but any attempt to update the node throws an error).
The iterator() method, by contrast, does not do any conversion of the result. It is returned
using its native Saxon representation, for example a String is returned as an instance of
sf.net.saxon.value.StringValue. You can then use all the methods available on this class
to process the returned value.
If you want to process the results of the query in your application, that's all there is to it. But you may want to output the results as serialized XML. Saxon provides two ways of doing this: you can produce wrapped output, or raw output. Raw output works only if the result consists of a single document or element node, and it outputs the subtree rooted at that element node in the form of a serialized XML document. Wrapped output works for any result sequence, for example a sequence of integers or a sequence of attribute and comment nodes; this works by wrapping each item in the result sequence as an XML element, with details of its type and value.
To produce wrapped output, you first wrap the result sequence as an XML tree, and then serialize the tree. To produce unwrapped output, you skip the wrapping stage and just call the serializer directly.
Both steps can be done using the QueryResult class. This class doesn't need to be
instantiated, its methods are static. The method QueryResult.wrap takes as input the iterator
produced by evaluating the query using the iterator() method, and produces as output
a DocumentInfo object representing the results wrapped as an XML tree. The method
QueryResult.serialize takes any document or element node as input, and writes it to
a specified destination, using specified output properties. The destination is supplied as an object
of class javax.xml.transform.Result. Like the Source, this is part of the
JAXP API, and allows the destination to be specified as a StreamResult (representing a byte stream or
character stream), a SAXResult (which wraps a SAX ContentHandler), or a DOMResult
(which delivers the result as a DOM). The output properties are used only when writing to
a StreamResult: they correspond to the properties available in the xsl:output element
for XSLT. The property names are defined by constants in the JAXP javax.xml.transform.OutputKeys
class (or net.sf.saxon.event.SaxonOutputKeys for Saxon extensions): for details of the
values that are accepted, see the JavaDoc documentation or the JAXP specification.
Michael H. Kay
Saxonica Limited
30 July 2010
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