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

Performing basic XQuery operations

We can use the XQueryExecutable instances created using XFactory.prepareXQuery methods to evaluate XQuery expressions. XQuery expressions can be passed to the XFactory.prepareXQuery method using a JAXP StreamSource object or using a plain Java string object. The resulting XQueryExecutable instance is thread safe and can be reused to evaluate an XQuery expression on multiple XML input documents.

• Use the XStaticContext object with the prepareXQuery method to pass in settings that affect how the XQuery expression is prepared.

  If no XStaticContext object is provided, the default setting is used.

  
  XStaticContext settings relevant to XQuery:

  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 XQuery expression

  declareVariable

  Declare a variable externally to be used as part of an XQuery 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.

  setBoundarySpacePolicy

  Specify whether to preserve or strip white space

  The options are as follows:

  BOUNDARY_SPACE_STRIP (default)

  BOUNDARY_SPACE_PRESERVE

  setConstructionMode

  Specify whether to preserve the type of element and attribute nodes or strip them

  The options are as follows:

  CONSTRUCTION_MODE_PRESERVE (default)

  CONSTRUCTION_MODE_STRIP

  setCopyNamespacesModeInherit

  Specify whether to inherit or ignore the namespace when copying element nodes

  The options are as follows:

  COPY_NAMESPACES_MODE_INHERIT (default)

  COPY_NAMESPACES_MODE_NO_INHERIT

  setCopyNamespacesModePreserve

  Specify whether to preserve or strip the namespace when copying element nodes

  The options are as follows:

  COPY_NAMESPACES_MODE_PRESERVE (default)

  COPY_NAMESPACES_MODE_NO_PRESERVE

  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".

  setDefaultOrderForEmptySequences

  Set the behavior for default order on empty sequences to greatest or least

  The options are as follows:

  DEFAULT_ORDER_FOR_EMPTY_SEQUENCES_LEAST (default)

  DEFAULT_ORDER_FOR_EMPTY_SEQUENCES_GREATEST

  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.

  setModuleResolver

  Set the module resolver used for module imports

  The default module resolution behavior is to attempt to locate one module for each location hint specified in the module import. The default resolution behavior for each location hint is to resolve relative URIs against the base URI from the static context, if the base URI is available, or to interpret them as file paths relative to the current working directory, if the base URI is not available. Absolute URIs are used unchanged. If a module cannot be located for a location hint, the processor ignores it unless no modules can be loaded for the namespace, in which case the processor emits an error message.

  setOrderingMode

  Specify whether the results returned by certain path expressions, union, intersect, and except expressions as well as FLWOR expressions that have no order by clause are ordered or unordered

  The options are as follows:

  ORDERING_MODE_ORDERED (default)

  ORDERING_MODE_UNORDERED

  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.

• Provide an XDynamicContext object that can be used to pass settings to the XQueryExecutable.execute method.

  These settings affect the behavior during the execution when the processor is evaluating an XQuery expression.

  If no XDynamicContext object is provided, the default setting is used.

  
  XDynamicContext settings relevant to XQuery:

  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 XQuery 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 execution-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.

• Execute XQuery expressions with schema awareness.

  To validate the input XML files with XQuery, schema files can be registered using the XFactory.registerSchema() method or users can declare the xsi:schemaLocation directive in their input XML files. In either case validation needs to be enabled using the XFactory.setValidating() method. XQuery only supports validating the input XML file for now.

Example

The following is a basic example of preparing and executing an interpreted XQuery expression.

// Create a string for the XQuery expression
String expression = "/doc/name[@first='David']";

// Create the factory
XFactory factory = XFactory.newInstance();

// Create the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression);

// Create the input XML source String xml = "<doc<name first='John'>Wrong</name><name first='David'>Correct</name></doc>";

// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));

The following is a basic example of preparing and executing a compiled XQuery expression.

// Create a string for the XQuery expression
String expression = "/doc/name[@first='David']";

// 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 the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression, xStaticContext);

// Create the input XML source String xml = "<doc><name first='John'>Wrong</name><name first='David'>Correct</name></doc>";

// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));

The following is a basic example of preparing and executing interpreted XQuery expressions with schema awareness.

// Create a string for the XQuery expression
String expression = "/my:doc/name[@first='David']/@first";
    
// 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:element name='doc'>"
                    +   "<xsd:complexType> "
                    +   "<xsd:sequence>"
                    +   "<xsd:element name='name' minOccurs='0' maxOccurs='unbounded'>"
                    +  "<xsd:complexType>"
                    +   "<xsd:attribute name='first' type='xsd:string' use='optional'/>"
                    +  "</xsd:complexType>"
                    +   "</xsd:element>"
                    +  "</xsd:sequence>"
                    +  "</xsd:complexType>"
                    + "</xsd:element>"
                    + "</xsd:schema>";
            
// Load the 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 a new namespace xStaticContext.declareNamespace("my", "http://www.schematype.ibm.com/UDSimple");
            
// Create the XQueryExecutable
XQueryExecutable xQueryExecutable = factory.prepareXQuery(expression, xStaticContext);
    
// Create the input XML source String xml = "<my:doc xmlns:my='http://www.schematype.ibm.com/UDSimple'>" +
              "<name first='John'/><name first='David'/></my:doc>";
    
// Execute the expression and store the results in an XSequenceCursor
XSequenceCursor xSequenceCursor = xQueryExecutable.execute(new StreamSource(new ByteArrayInputStream(xml.getBytes())));

Related

Use static and dynamic contexts
Use external functions
Use external functions with XQuery
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 XQuery
Use a source resolver at execution time
Registering a collection resolver
Work with collations

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