Try this :
CallableStatement cStmt = con.prepareCall("{? = call verifierQteDemandee(?)}");
cStmt.registerOutParameter(1,java.sql.Types.BOOLEAN);
cStmt.setInt(2, 42);
cStmt.execute();
Boolean outputValue = cStmt.getBoolean(1);
Ça devrais fonctionner...!