You can use the XPathExecutable instances that are created
using XFactory.prepareXPath methods to evaluate XPath expressions.
About this task
XPath expressions can be passed to the XFactory.prepareXPath
method using a JAXP StreamSource object or using a plain Java string object. The resulting XPathExecutable
instance is thread safe and can be reused to evaluate an XPath expression
on multiple XML input documents.
Procedure
- Use the XStaticContext object with the prepareXPath method
to pass in settings that affect how the XPath expression is prepared.
If no XStaticContext object is provided, the default setting
is used.
XStaticContext settings relevant to XPath: - declareFunction
- Declare a Java extension
function
- declareNamespace
- Declare a namespace prefix and associate it with a namespace URI
to be used as part of an XPath expression
- declareVariable
- Declare a variable externally to be used as part of an XPath expression
- setBaseURI
- Set the base URI used in the resolution of relative URIs (such
as by the fn:resolve-uri function)
The default is the base URI of
the expression, query, or stylesheet if the base URI is available.
If the base URI is not available, the current working directory is
used.
- setDefaultCollation
- Set the default collation URI for string comparison operations
The
default is the Unicode code point collation URI.
- setDefaultElementTypeNamespace
- Specify the URI of the default element or type namespace
Use
an empty string to make it unspecified.
The default is an empty
string.
- setDefaultFunctionNamespace
- Specify the URI of the default function namespace
Use an empty
string to make it unspecified.
The default is "http://www.w3.org/2005/xpath-functions".
- setIntegerMathMode
- Set the integer math mode to one of the following:
- INTEGER_MATH_MODE_LIMITED_PRECISION
- Limit to 18-digit precision for xs:integer (default)
- INTEGER_MATH_MODE_ARBITRARY_PRECISION
- Allow users to have arbitrary precision for xs:integer
- INTEGER_MATH_MODE_OVERFLOW_DETECTION
- Generate an error if an overflow is detected
- setMessageHandler()
- Set the message handler for prepare-time errors
The default
behavior is to print errors, warnings, and informational messages
to System.err and to generate an XProcessException in the case of
an unrecoverable error when compilation cannot continue. If the message
handler that is registered does not generate its own
exception in the case of an unrecoverable error, an XProcessException
occurs.
- setUseCompiler
- Indicate whether to generate a compiled executable or an interpreted
executable
A compiled executable takes longer to generate but runs
faster than an interpreted executable. The default is interpreted.
- setXPathCompatibilityMode
- Sets the compatibility mode to be used when evaluating XPath expressions
The
options are as follows:
- XPATH2_0_PURE_COMPATIBILITY (default)
- Use the default behavior defined by XPath 2.0 in evaluating expressions.
- XPATH1_0_BC_COMPATIBILITY
- Use the backwards-compatibility behavior defined by XPath 2.0
that yields results that are most consistent with those that would
be produced by an XPath 1.0 processor.
- XPATH_LATEST_VERSION
- Use the default behavior defined by the most recent version of
XPath supported by the processor.
- Provide an XDynamicContext object that can be used to pass
settings to the XPathExecutable.execute method.
These
settings affect the behavior during the execution when the processor
is evaluating an XPath expression.
If no XDynamicContext object
is provided, the default setting is used.
XDynamicContext
settings relevant to XPath:- bind
- Bind a value to an external variable
- bindCollation
- Binds an instance of the java.text.Collator class to a particular
collation URI for use in string comparisons that use that collation
URI
- bindFunction
- Bind an external function so that it can be used as part of an
XPath expression
- bindSequence
- Bind a sequence value to an external variable
- setCollectionResolver
- Set the collection resolver used to resolve documents loaded with
the XPath fn:collection function
The default behavior is for references
to the fn:collection function to return an empty sequence.
- setImplicitTimeZone
- Set the implicit time zone
The default is to use the system
time zone as retrieved through the Java method
java.util.TimeZone.getDefault().
- setMessageHandler()
- Set the message handler for excution-time errors
The default
behavior is to print errors, warnings and informational messages to
System.err and to generate an XProcessException in the case of an
unrecoverable error. If the message handler that is registered does
not generate its own exception in the case of an unrecoverable error,
an XProcessException occurs.
- setSourceResolver
- Set the source resolver used to resolve documents loaded with
the XPath fn:doc function
The default behavior is to resolve documents
based on the base URI from the static context. If the base URI is
not available, the current working directory is used.
- Use schemas with XPath expression evaluation.
For
schema-aware XPath evaluation and validating the input XML file, schema
files can be registered using the XFactory.registerSchema() method
or you can declare the xsi:schemaLocation directive in their input
XML files. In either case, validation needs to be enabled using the
XFactory.setValidating() method.
Example
The following is a basic example of preparing and executing
an interpreted XPath expression.
// Create a string for the XPath expression
String expression = "/doc/something";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create an XPath executable for the expression
XPathExecutable xPathExecutable = factory.prepareXPath(expression);
// Create the input XML source
String xml = "<doc><something>something is selected</something></doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xPathExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));
The
following is a basic example of preparing and executing a compiled
XPath expression.
// Create a string for the XPath expression
String expression = "/doc/something";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create a new static context from the factory
XStaticContext xStaticContext = factory.newStaticContext();
// Set the mode to compile for the processor
xStaticContext.setUseCompiler(true);
// Create an XPath executable for the expression
XPathExecutable xPathExecutable = factory.prepareXPath(expression, xStaticContext);
// Create the input XML source
String xml = "<doc><something>something is selected</something></doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xPathExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));
The
following is a basic example of preparing and executing interpreted
XPath expressions with schema validation.
// Create a string for the XPath expression
String expression = "/doc/byte cast as my:derived1-byte-enumeration-Type";
// Create the factory
XFactory factory = XFactory.newInstance();
// Create the schema source
String schema = "<xsd:schema xmlns:xsd='http://www.w3.org/2001/XMLSchema'" +
" targetNamespace='http://www.schematype.ibm.com/UDSimple'" +
" xmlns:my='http://www.schematype.ibm.com/UDSimple'" +
" xmlns:smokey='http://www.schematype.ibm.com/UDSimple'>"
+ " <xsd:simpleType name='derived1-byte-enumeration-Type'>"
+ " <xsd:restriction base='xsd:byte'>"
+ " <xsd:enumeration value='1' />"
+ " <xsd:enumeration value='-1' />"
+ " <xsd:enumeration value='0' />"
+ " <xsd:enumeration value='127' />"
+ " <xsd:enumeration value='-128' />"
+ " <xsd:enumeration value='32' />"
+ " <xsd:enumeration value='-32' />"
+ " <xsd:enumeration value='8' />"
+ " <xsd:enumeration value='-8' />"
+ " <xsd:enumeration value='2' />"
+ " <xsd:enumeration value='-2' />"
+ " </xsd:restriction>"
+ " </xsd:simpleType>"
+ "</xsd:schema>";
// Load schema
factory.registerSchema(new StreamSource(new ByteArrayInputStream(schema.getBytes())));
// Turn on validation
factory.setValidating(true);
// Create a new static context from the factory
XStaticContext xStaticContext = factory.newStaticContext();
// Add new namespace
xStaticContext.declareNamespace("my", "http://www.schematype.ibm.com/UDSimple");
// Create an XPath executable for the expression
XPathExecutable xPathExecutable = factory.prepareXPath(expression, xStaticContext);
// Create the input XML source
String xml = "<doc>" +
" <byte>1</byte>" +
"</doc>";
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xPathExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));