Performing basic XPath operations

WAS v8.5 > Develop applications > XML applications > Use the XML API to perform operations > Performing basic operations
Performing basic XPath operations

We can use the XPathExecutable instances created using XFactory.prepareXPath methods to evaluate XPath expressions. 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.

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 we 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())));
Related

Use static and dynamic contexts
Use external functions
Use external functions with XPath
Use a source resolver at prepare time
Use a message handler
Use a message handler and managing exceptions
Choose between the compiler and the interpreter
Use external variables
Use external variables with XPath
Use a source resolver at execution time
Registering a collection resolver
Work with collations

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