javax.xml.xquery
Interface XQPreparedExpression

All Superinterfaces:

XQDynamicContext

All Known Implementing Classes:

SaxonXQPreparedExpression

public interface XQPreparedExpression
extends XQDynamicContext

This interface describes an expression that can be prepared for multiple subsequent executions. A prepared expression can be created from the connection.

The preparation of the expression does the static analysis of the expression using the static context information.

The dynamic context information, such as values for bind variables, can then be set using the setter methods. When setting values for bind variables, these variables should be present as external variables in the prolog of the prepared expression.

The static type information of the query can also be retrieved if the XQuery implementation provides it using the getStaticResultType method.

When the expression is executed using the executeQuery method, if the execution is successful, then an XQResultSequence object is returned. The XQResultSequence object is tied to the XQPreparedExpression from which it was prepared and is closed implicitly if that expression is either closed or if re-executed.

The XQPreparedExpression object is dependent on the XQConnection object from which it was created and is only valid for the duration of that object. Thus, if the XQConnection object is closed then this XQPreparedExpression object will be implicitly closed and it can no longer be used.

An XQJ driver is not required to provide finalizer methods for the connection and other objects. Hence it is strongly recommended that users call close method explicitly to free any resources. It is also recommended that they do so under a final block to ensure that the object is closed even when there are exceptions. Not closing this object implicitly or explicitly might result in serious memory leaks.

When the XQPreparedExpression is closed any XQResultSequence object obtained from it is also implicitly closed.

Example -

  XQConnection conn = XQDataSource.getconnection();
  XQPreparedExpression expr = conn.prepareExpression
          ("for $i in (1) return 'abc' "); 
 
  // get the sequence type out.. This would be something like xs:string *
  XQSequenceType type = expr.getStaticResultType();

  XQSequence result1 = expr.executeQuery();
 
  // process the result..
  result1.next();
  System.out.println(" First result1 "+ result1.getAtomicValue());

  XQResultSequence result2 = expr.executeQuery();

  // result1 is implicitly closed 
  // recommended to close the result sequences explicitly.

  // process the result..
  while (result2.next()) 
     System.out.println(" result is "+ result2.getAtomicValue());
 
  result2.close(); 
  expr.close(); // closing expression implicitly closes all result sequence or
                // items obtained from this expression.
  conn.close(); // closing connections will close expressions and results.
 

Method Summary

void	cancel() Attempts to cancel the execution if both the XQuery engine and XQJ driver support aborting the execution of an XQPreparedExpression.
void	close() Closes the expression object and release all resources associated with this prepared expression.
XQResultSequence	executeQuery() Executes the prepared query expression.
QName[]	getAllExternalVariables() Retrieves all the external variables defined in the prolog of the prepared expression.
QName[]	getAllUnboundExternalVariables() Retrieves the names of all unbound external variables.
XQStaticContext	getStaticContext() Gets an XQStaticContext representing the values for all expression properties.
XQSequenceType	getStaticResultType() Gets the static type information of the result sequence.
XQSequenceType	getStaticVariableType(QName name) Retrieves the static type of a given external variable.
boolean	isClosed() Checks if the prepared expression in a closed state.

Methods inherited from interface javax.xml.xquery.XQDynamicContext

bindAtomicValue, bindBoolean, bindByte, bindDocument, bindDocument, bindDocument, bindDocument, bindDocument, bindDouble, bindFloat, bindInt, bindItem, bindLong, bindNode, bindObject, bindSequence, bindShort, bindString, getImplicitTimeZone, setImplicitTimeZone

Method Detail

cancel

void cancel()
            throws XQException

Attempts to cancel the execution if both the XQuery engine and XQJ driver support aborting the execution of an XQPreparedExpression. This method can be used by one thread to cancel an XQPreparedExpression, that is being executed in another thread. If cancellation is not supported or the attempt to cancel the execution was not successful, the method returns without any error. If the cancellation is successful, an XQException is thrown, to indicate that it has been aborted, by executeQuery, executeCommand or any method accessing the XQResultSequence returned by executeQuery. If applicable, any open XQResultSequence and XQResultItem objects will also be implicitly closed in this case.

Throws:

XQException - if the prepared expression is in a closed state

isClosed

boolean isClosed()

Checks if the prepared expression in a closed state.

Returns:

true if the prepared expression is in a closed state, false otherwise.

close

void close()
           throws XQException

Closes the expression object and release all resources associated with this prepared expression. This also closes any result sequences obtained from this expression. Once the expression is closed, all methods on this object other than the close or isClosed will raise exceptions. Calling close on an XQExpression object that is already closed has no effect.

Throws:

XQException - if there are errors when closing the expression

executeQuery

XQResultSequence executeQuery()
                              throws XQException

Executes the prepared query expression. Calling this method implicitly closes any previous result sequence obtained from this expression.

Returns:

the xquery sequence object containing the result of the query execution

Throws:

XQException - if (1) there are errors when executing the prepared expression, (2) the prepared expression is in a closed state, or (3) the query execution is cancelled

getAllExternalVariables

QName[] getAllExternalVariables()
                                throws XQException

Retrieves all the external variables defined in the prolog of the prepared expression.

Returns:

an array of QName objects for all the external variables defined in the prolog of a prepared expression. Empty array if there are no external variables present.

Throws:

XQException - if the prepared expression is in a closed state

getAllUnboundExternalVariables

QName[] getAllUnboundExternalVariables()
                                       throws XQException

Retrieves the names of all unbound external variables.

Returns:

the QName for all the external variables defined in the prolog of a prepared expression that are yet to be bound with a value. If there are no such variables an empty array is returned

Throws:

XQException - if the prepared expression is in a closed state

getStaticResultType

XQSequenceType getStaticResultType()
                                   throws XQException

Gets the static type information of the result sequence. If an implementation does not do static typing of the query, then this method must return an XQSequenceType object corresponding to the XQuery sequence type item()*.

Returns:

XQSequenceType containing the static result information.

Throws:

XQException - if the prepared expression is in a closed state

getStaticVariableType

XQSequenceType getStaticVariableType(QName name)
                                     throws XQException

Retrieves the static type of a given external variable.

Parameters:

name - the name of the external variable

Returns:

the static type information of the variable as defined in the prolog of the prepared expression

Throws:

XQException - if (1) the variable does not exist in the static context of the expression, or (2) the sequence is in a closed state, or (3) the name parameter is null

getStaticContext

XQStaticContext getStaticContext()
                                 throws XQException

Gets an XQStaticContext representing the values for all expression properties. Note that these properties cannot be changed; in order to change, a new XQPreparedExpression needs to be created.

Returns:

an XQStaticContext representing the values for all expression properties

Throws:

XQException - if the expression is in a closed state