Package net.sf.saxon.query

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 TreeInfo interface.

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:

  • Values of parameters (external global variables). You can set these using the 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 in the main Saxon documentation under "Converting Java values to XDM values".
  • The context item can be set using the method setContextItem().
  • You can also set a URIResolver and/or ErrorListener. These default to the ones that were used during Query compilation.

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.om.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.lib.SaxonOutputKeys for Saxon extensions): for details of the values that are accepted, see the JavaDoc documentation or the JAXP specification.