javax.xml.xquery
public interface XQExpression extends XQDynamicContext
XQConnection
and the execution can be done using the executeQuery()
or
executeCommand()
method, passing in the XQuery expression.
All external variables defined in the prolog of the expression to be executed must
be set in the dynamic context of this expression using the bind methods.
Also, variables bound in this expression but not defined as external in
the prolog of the expression to be executed, are simply ignored.
For example, if variables $var1
and $var2
are bound,
but the query only defines $var1
as external, no error
will be reported for the binding of $var2
. It will simply
be ignored.
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 XQExpression
from which it was prepared and is
closed implicitly if that XQExpression
is either closed or re-executed.
The XQExpression
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 XQExpression
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 XQExpression
is closed any XQResultSequence
object obtained from it is also implicitly closed.
Example -
XQConnection conn = XQDatasource.getConnection(); XQExpression expr = conn.createExpression(); expr.bindInt(new QName("x"), 21, null); XQSequence result = expr.executeQuery( "declare variable $x as xs:integer external; for $i in $x return $i"); while (result.next()) { // process results ... } // Execute some other expression on the same object XQSequence result = expr.executeQuery("for $i in doc('foo.xml') return $i"); ... result.close(); // close the result expr.close(); conn.close();
Method Summary | |
---|---|
void | cancel()
Attempts to cancel the execution if both the XQuery engine and XQJ
driver support aborting the execution of an XQExpression . |
void | close()
Closes the expression object and release associated resources.
|
void | executeCommand(String cmd)
Executes an implementation-defined command.
|
void | executeCommand(Reader cmd)
Executes an implementation-defined command.
|
XQResultSequence | executeQuery(String query)
Executes a query expression. |
XQResultSequence | executeQuery(Reader query)
Executes a query expression. |
XQResultSequence | executeQuery(InputStream query)
Executes a query expression. |
XQStaticContext | getStaticContext()
Gets an XQStaticContext representing the values for all
expression properties. |
boolean | isClosed()
Checks if the expression is in a closed state.
|
XQExpression
. This method can
be used by one thread to cancel an XQExpression
, 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 expression is in a closed state
close
or isClosed
will raise exceptions.
This also closes any result sequences obtained from this expression.
Calling close
on an XQExpression
object
that is already closed has no effect.
Throws: XQException if there are errors when closing the expression
Parameters: cmd the input command as a string
Throws: XQException if (1) there are errors when executing the command, or (2) the expression is in a closed state
Parameters: cmd the input command as a string reader
Throws: XQException if (1) there are errors when executing the command, (2) the expression is in a closed state, or (3) the execution is cancelled
Parameters: query the input query expression string.
Cannot be null
Returns: an XQResultSequence
object containing
the result of the query execution
Throws: XQException if (1) there are errors when executing the query,
(2) the expression is in a closed state,
(3) the execution is cancelled,
(4) the query parameter is null
Parameters: query the input query expression as a reader object.
Cannot be null
Returns: an XQResultSequence
object containing
the result of the query execution
Throws: XQException if (1) there are errors when executing the query,
(2) the expression is in a closed state,
(3) the execution is cancelled, or
(4) the query parameter is null
Parameters: query the input query expression as a input stream object.
Cannot be null
Returns: an XQResultSequence
containing the
result of the query execution
Throws: XQException if (1) there are errors when executing the query,
(2) the expression is in a closed state,
(3) the execution is cancelled, or
(4) the xquery parameter is null
XQStaticContext
representing the values for all
expression properties. Note that these properties cannot be changed; in
order to change, a new XQExpression
needs to be created.
Returns: an XQStaticContext
representing
the values for all expression properties
Throws: XQException if the expression is in a closed state
Returns: true
if the expression is in
a closed state, false
otherwise