Performing basic XPath operations

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())));