dbms_lob.getlength

SQL

SELECT dbms_lob.getlength(CSUSERATTACHEDFILE01.FILECONTENT) AS blobLength
  FROM CSUSERATTACHEDFILE CSUSERATTACHEDFILE01
 WHERE (CSUSERATTACHEDFILE01.CSUSERATTACHEDFILENO=10291)

XML query API

<query alias="testLobLength" projectedClass="com.taleo.akirademo.entity.AttachedFile">
    <projections>
        <projection alias="blobLength">
            <lobLength>
                <field path="fileContent"/>
            </lobLength>
        </projection>
    </projections>
    <filterings>
        <filtering>
            <equal>
                <field path="no"/>
                <integer>10291</integer>
            </equal>
        </filtering>
     </filterings>
</query>