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From "Fitzgibbons, Brad" <bfitzgibb...@techtarget.com>
Subject RE: RowIterator.next() fails when hasNext() returns true
Date Mon, 14 Jul 2008 13:26:18 GMT
Here's one more thing I thought of that might be helpful.  I can create a query where I expect
exactly one result that exhibits the hasNext/next behavior.  However, when I mask it as shown
below I still get just the one expected result.  This goes to what I meant by "normal" behavior
when masking the error.

Thanks for your help!
brad

-----Original Message-----
From: Fitzgibbons, Brad
Sent: Monday, July 14, 2008 9:04 AM
To: 'users@jackrabbit.apache.org'
Subject: RE: RowIterator.next() fails when hasNext() returns true

Yes, it's threadsafe.  Each visit to the URL invokes the resourceQueryAndPrint() method. 
This method is wrapped in a JTA transaction, and results in the following actions:
    (1) Execute a new SQL query on the JCR session (using spring-modules to provide session).
    (2) Create a new instance of PropertyIterator which wraps the RowIterator from the query.
    (3) Perform the loop as shown and print some of the metadata from each element in the
result set.
        (a) Each call to PropertyIterator.hasNext() delegates to RowIterator.hasNext().
        (a) Each call to PropertyIterator.next() will marshall data from the Row returned
by RowIterator.next() into a DTO.

Here's an example of the SQL query (with actual property names and node primary type changed):
    select A,B,C,D from custom_type where (A='A1' or A='A2' or A='A3') and (contains(B, 'XXX')
or contains(C, 'XXX')) order by D

Changing the properties in the select clause or the order by clause (but leaving the where
clause as-is) will sometimes produce iterators that do not have the hasNext/next behavior
I've described.


-----Original Message-----
From: Marcel Reutegger [mailto:marcel.reutegger@gmx.net]
Sent: Monday, July 14, 2008 8:40 AM
To: users@jackrabbit.apache.org
Subject: Re: RowIterator.next() fails when hasNext() returns true

Hi,

hmm, let's check something else... what about your class ProfileController, is it thread-safe?
is it possible that two threads concurrently call hasNext/next?
is PropertyIterator in ProfileController an instance variable?

regards
  marcel

Fitzgibbons, Brad wrote:
> Yes.  My loop breaks down to this:
>
> while (iterator.hasNext()) {
>    Object obj = iterator.next();
>    ...
> }
>
> However, if I do this instead I get (what appears to be) "normal" behavior (except that
getSize() is often much less than the actual result set size):
>
> while (iterator.hasNext()) {
>     try {
>         Object obj = iterator.next();
>     } catch (NoSuchElementException excp) { /* masked */ } }
>
> Thanks!
> brad
>
> -----Original Message-----
> From: Marcel Reutegger [mailto:marcel.reutegger@gmx.net]
> Sent: Monday, July 14, 2008 4:35 AM
> To: users@jackrabbit.apache.org
> Subject: Re: RowIterator.next() fails when hasNext() returns true
>
> Hi,
>
> this seems very strange because LazyScoreNodeIterator always pre-fetches the next node.
so whenever you call hasNext() and it returns true LazyScoreNodeIterator already has the next
node and does not have to fetch it on nextRow().
>
> Can you please double check that you always call hasNext() before you
> call
> nextRow() ?
>
> regards
>   marcel
>
> Fitzgibbons, Brad wrote:
>> I'm running into this problem occasionally resulting in the exception
>> below.  I'm using Jackrabbit 1.4 (with core at 1.4.2).  I'm using the
>> H2PersistenceManager and almost all configuration values are set to
>> their released default. Document order is turned off so the query is
>> using a LazyScoreNodeIterator.  I'm running in a transactional
>> environment, and my entire execution flow is contained by a single,
>> read-only, JTA transaction.  The single transaction includes
>> executing the query and all interactions with the returned
>> RowIterator.  If I ignore the NoSuchElementException's and continue
>> using the iterator then there are often good results subsequent to
>> the error.  I've noticed that when these errors occur there are often
>> far more results than are returned by RowIterator.getSize().  I
>> realize that getSize() is not meant to be an accurate count of all
>> results, but in most other cases getSize() is greater than the size
>> of the result set (this may not be helpful).  I'm using
>  a SQL query that involves the CONTAINS constraint (so lucene) and ordering by jcr:score.
 Does this warrant a bug submission?  Is there any additional information which might help?
>> org.springframework.web.util.NestedServletException: Request processing failed; nested
exception is java.util.NoSuchElementException
>>         at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:535)
>>         at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:453)
>>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
>>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
>>         at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
>>         at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:181)
>>         at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:266)
>>         at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:269)
>>         at com.caucho.server.port.TcpConnection.run(TcpConnection.java:603)
>>         at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:721)
>>         at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:643)
>>         at java.lang.Thread.run(Thread.java:619)
>> Caused by: java.util.NoSuchElementException
>>         at org.apache.jackrabbit.core.query.lucene.QueryResultImpl$LazyScoreNodeIterator.getScore(QueryResultImpl.java:351)
>>         at org.apache.jackrabbit.core.query.lucene.RowIteratorImpl.nextRow(RowIteratorImpl.java:153)
>>         at com.techtarget.content.data.jcr1.ElementDaoImpl.nextElement(ElementDaoImpl.java:722)
>>         at com.techtarget.content.data.jcr1.PropertyIterator.next(PropertyIterator.java:47)
>>         at com.techtarget.content.data.jcr1.PropertyIterator.next(PropertyIterator.java:21)
>>         at com.techtarget.content.web.controller.ProfileController.resourceQueryAndPrint(ProfileController.java:125)
>>         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>>         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
>>         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>>         at java.lang.reflect.Method.invoke(Method.java:597)
>>         at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.doInvokeMethod(HandlerMethodInvoker.java:305)
>>         at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:131)
>>         at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:308)
>>         at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:295)
>>         at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:874)
>>         at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:808)
>>         at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:523)
>>         at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:453)
>>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
>>         at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
>>         at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
>>         at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:181)
>>         at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:266)
>>         at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:269)
>>         at com.caucho.server.port.TcpConnection.run(TcpConnection.java:603)
>>         at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:721)
>>         at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:643)
>>         at java.lang.Thread.run(Thread.java:619)
>>
>> Brad Fitzgibbons
>> Senior Software Engineer
>> Tech Target
>> The Most Targeted IT Media
>> http://www.techtarget.com/
>>
>>
>>
>
>


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