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Retrieving Query Results

DataDirect XQuery® is carefully designed to allow very large query results to be retrieved efficiently, and to allow incremental instantiation of query results, so that memory can also be used efficiently. If your query's results can be large, stream the results to an OutputStream or use SAX or StAX, so that retrieving the results does not introduce issues with memory or performance. Retrieving large query results as DOM can use large amounts of memory and significantly increase the time needed for processing queries.

If you want to write your query results to an output stream or a file, the easiest way is to use the writeSequence() method of the result set to write directly to the stream, as shown in the following code.

Example 11. Writing a Result Sequence to a Stream

    XQSequence sequence =  expression.executeQuery(query);
    OutputStream os = new FileOutputStream("C:/temp/results.xml");
    sequence.writeSequence(os);         
            

Many XML programs process XML using SAX, and DataDirect XQuery® can write query results directly to a SAX event handler, as shown in the following code.

Example 12. Writing to a SAX Event Handler

    CustomSAXEventHandler eventHandler = new CustomSAXEventHandler();
    sequence.writeSequenceToSAX(eventHandler);            
            

For many kinds of programming, pull processing using StAX is both convenient and efficient. You can get a StAX stream from a result sequence using the getSequenceAsStream() method:

Example 13. Retrieving Results as a StAX Stream

    XMLStreamReader reader = sequence.getSequenceAsStream();