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Package net.sf.saxon.s9api.streams

This package (introduced in Saxon 9.9) provides methods to manipulate XDM values using Java 8 streams.

See: Description

Package net.sf.saxon.s9api.streams Description

This package (introduced in Saxon 9.9) provides methods to manipulate XDM values using Java 8 streams.

A value in the XDM data model is represented by an instance of XdmValue. This is in general a sequence; the members of the sequence are instances of XdmItem. XdmItem is an abstract class; its concrete subclasses include XdmNode for nodes, XdmAtomicValue for atomic values, XdmFunctionItem for function items, XdmMap for maps, and XdmArray for arrays.

Given an XdmNode N, it is possible to select other nodes using an expression such as N.select(child("author")).asNode(). The way this works is as follows:

The power of the approach rests in the range of Step implementations available, and the way these can be combined; and in the terminal operations to deliver the result of a stream in a useful way. Although many standard implementations are available, these can be augmented with user-written methods; since a Step is just a Java 8 Function, and an XdmStream is just a Java 8 Stream, all the standard Java 8 facilities for creating and combining functions and streams are available.

Steps

The steps that are available "off the shelf" from the Steps class include the following:

Predicates

Predicates can be used either in the where() method to construct a new Step, or they may be used in the standard Java 8 filter() method to filter the items in a stream. Any predicate may be used in either context. The utility class Predicates provides a range of predicates that are particularly suited to XDM navigation.

These predicates include:

Operations on XDM streams

An XdmStream (as delivered by XdmValue.select(step)) is an implementation of a Java 8 Stream, so all the standard methods on Stream are available: for example filter, map(), flatMap, reduce, collect. Where appropriate, these are specialized to return an XdmStream rather than a generic Stream.

XdmStream provides some additional terminal operations designed to make it convenient to convert the contents of the stream into usable form. These include:

The choice of terminal operation determines the return type (for example asOptionalNode() returns Optional<XdmNode>), and also causes a run-time check that the value actually conforms to these expectations. For example, if asNode() is used, then an unchecked exception occurs if the sequence has a length other than 1 (one), or if its single item is not a node.

Other ways of generating an XdmStream include:


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