Greetings,
I was unsure where to post this (perhaps the developer list?), but
decided here was as good as any. I've uncovered a bug and am unsure what
to attribute it to, so thought this would be a good forum. I have worked
around the problem, but hoped I could contribute something useful here.
Please let me know if there is a better place to post this.
The problem:
When executing a call to PersistenceBroker.getCollectionByQuery(query),
where setStartAtIndex(1) has been called on query, a NullPointerException
is thrown with the following stacktrace:
Exception in thread "main" java.lang.NullPointerException
at com.mysql.jdbc.ResultSet.getRow(ResultSet.java:1632)
at org.apache.ojb.broker.accesslayer.RsIterator.size(Unknown
Source)
at
org.apache.ojb.broker.singlevm.PersistenceBrokerImpl.getCollectionByQuery(Unknown
Source)
at
org.apache.ojb.broker.singlevm.PersistenceBrokerImpl.getCollectionByQuery(Unknown
Source)
at
org.apache.ojb.broker.singlevm.PersistenceBrokerImpl.getCollectionByQuery(Unknown
Source)
at
org.apache.ojb.broker.singlevm.PersistenceBrokerImpl.getCollectionByQuery(Unknown
Source)
at
org.apache.ojb.broker.singlevm.DelegatingPersistenceBroker.getCollectionByQuery(Unknown
Source)
at
edu.arizona.ltc.authentication.UserDAO.findAllUsers(UserDAO.java:168)
at edu.arizona.ltc.authentication.UserDAO.main(UserDAO.java:199)
The problem is avoided by omitting the call to setStartAtIndex, or by
setting startAtIndex to zero. Certainly this is an off-by-one error, I
thought.
HOWEVER! If I ensure that there are multiple rows in the UserData table,
this exception is still thrown. I am writing because I believe there may
be either a) an error in the MySQL driver and a related gap in error
handling in RsIterator, or b) a flaw in the logic of RsIterator (perhaps
a need to check the fetchSize of the ResultSet?). [I am of course
willing to consider c) I am doing something stupid and wrong... but I am
certain that I will be corrected in this forum if that is the case ;) ]
Background (for anyone interested in the details):
I am developing a web application for the University of Arizona and have
been using Wrox Press' "Professional Struts Applications; Building Web
Sites with Struts, ObjectRelationalBridge, Lucene, and Velocity" (kudos to
the authors - a good guide IMHO for web application and/or Apache Jakarta
newbies). I intend to use their example application as a template for the
core of my application.
I am currently addressing the use of OJB to create a data access tier. I
originally intended to use postgresql beneath OJB but could never get the
OJB tutorials to successfully run. I switched to MySQL. To start I have
done a simple implementation of a user account system. User information
is in a table called UserData:
+----------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+--------------+------+-----+---------+-------+
| agent_id | int(11) | | PRI | 0 | |
| user_login | varchar(20) | YES | | NULL | |
| user_title | varchar(5) | YES | | NULL | |
| user_firstname | varchar(50) | YES | | NULL | |
| user_lastname | varchar(50) | YES | | NULL | |
| user_email | varchar(255) | YES | | NULL | |
| user_phone | varchar(50) | YES | | NULL | |
+----------------+--------------+------+-----+---------+-------+
UserData is mapped to an User class, with simple get/set methods for all
of the above types. Retrieving by primary key properly populates the User
object, giving me confidence that I have appropriately configured
repository_user.xml
UserDAO in the stacktrace above simply wraps the logic of aquiring a
PersistenceBroker reference, creating Criteria and Query objects and
executing transactions. The code for findAllUsers() method is as follows
(offending line has been commented out):
public Collection findAllUsers() throws DataAccessException
{
PersistenceBroker broker = null;
Collection results = null;
try
{
Criteria crit = new Criteria();
crit.addOrderByDescending ("user_login");
Query query = QueryFactory.newQuery (User.class, crit);
// query.setStartAtIndex (1);
broker = ServiceLocator.getInstance().findBroker();
results = (Collection) broker.getCollectionByQuery(query);
}
catch (ServiceLocatorException sle)
{
throw new DataAccessException
("Error in UserDAO.findAllUsers(): " + sle.getMessage(), sle);
}
finally
{
if (broker != null)
{
broker.close();
}
}
return results;
}
Thanks much,
Duffy
=====================================
Duffy Gillman
POLIS Systems Programmer
Learning Technology Center
PO Box 210073, CCIT Bldg., Rm. 337
1077 N. Highland Ave.
Tucson, AZ 85721-0073
520.626.0117 (voice)
520.626.8220 (fax)
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