Entries for March 2006, Colin's blog

March 27, 2006

Threading in JBoss, hibernate + spring

The project I am currently working on has an OM which looks like:

page -> content -> contentFetcher

The page typically has 4 contents (links, toolbars, main and rhs) which are sequentially loaded. This seems like a good candidate for threading; there are no dependencies between them and they are each potentially expensive to created (coming from remote servers etc.).

As an experiment I wrapped added the call to retrieve them in it's own thread and deployed. Unfortunately it all went horribly wrong….and (I think) it is because we are using spring OSIV which creates a single session for the entire thread. The stack trace is:


java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:787)
        at java.util.HashMap$ValueIterator.next(HashMap.java:817)
        at org.hibernate.pretty.Printer.toString(Printer.java:90)
        at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListen
er.java:97)
        at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26)
        at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1009)
        at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:356)
        at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
        at org.springframework.orm.hibernate3.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:584)

which is a shame.

(As an aside, it is OK to create threads within JBoss, or rather to retrieve threads from a custom threadpool; thus allowing JBoss to shut down without your threads holding anything up.)

I am sure I can work around this, and I have only spent 5 minutes on this so far, but I don't think we will be able to use SessionPerView…..

P.S link

: 27 Mar 2006 15:13 | Tags: JBoss Spring Thread | Comments (0) | Close comments | Report a problem

Charsets ; I hate them :(

So the project I am working on uses a number of technologies including JSTL and freemarker.

Somebody had entered the following character: "è" which was displaying perfectly in JSP, but freemarker was replacing it with "?".

Of course I thought, it must be freemarkers fault :) I was meticulously careful about never converting a byte[] into a String using the string constructor unless the charset was specified, but I never realised you had to do it the other way as well :( When calling getBytes(), the encoding of the string is completely ignored and the platform default is used…. Why?

So the following will do bad things:


  new String(new String("some string with a funny character è", encoding).getBytes(), encoding);

lame.

The problem was also a little bit more interesting because on windows machines the default platform is unicode based, on solaris it isn't, so the problem only exhibited itself on solaris.

I have (I am ashamed to say) never really delved into the joy of charsets and text encoding, instead preferring to stick my head in the sand. Luckily Chris May sits next on the desk next to me :)

: 27 Mar 2006 13:47 | Comments (3) | Close comments | Report a problem

March 21, 2006

Expert Spring MVC + Spring Web Flow errata

Writing about web page http://apress.com/book/bookDisplay.html?bID=10048

Below are the changes in Chapter 11 + Chapter 12 as a result of upgrading to Spring Web Flow 1.0 EA:

[global changes]
_flowExecutionId has been renamed to _flowExecutionKey
org.springframework.webflow.manager has been renamed to org.springframework.webflow.executor
FlowExecutionManager has been renamed to FlowExecutor
FlowExecutionManagerImpl has been renamed to FlowExecutorImpl
FlowExecutionContinuationKey has been renamed to FlowExecutionKey
FlowExecutionManagerParameterExtractor has been renamed to FlowExecutorArgumentExtractor

Chapter 11

– Figure 11–3 (page 7) has four boxes which all contain text starting "webflow.manager.". The word "manager" needs to be replaced with the word "executor", i.e the first box should read webflow.executor.struts.FlowAction etc.

– The first line of the last paragraph on page 7 refers to "FlowExecutionManager". This has been renamed to "FlowExecutor".

– Page 8 refers to "org.springframework.webflow.execution.FlowExecutionRepository". This has been renamed to "org.springframework.webflow.execution.repository.FlowExecutionRepository".

– Page 17 refers to "AbstractFlowexecutionTests" but the e after "Flow" should be capitalised: "AbstractFlowExecutionTests".

– The first two methods in Listing 11–8 are duplicates. Please remove the first method. The second method needs to change from:

protected Resource getFlowLocation() {

File flowDir = new File(.......);

return new FileSyste…..
}

to:

protected Resource getFlowLocation() {

File flowDir = new File(.......);

FileSystemResource resource = new FileSystemResource(new File(flowDir, "purchase-flow.xml"));

return new ExternalizedFlowDefinition("purchaseFlow", resource);
}

so essentially the first line stays the same, and the second line is replaced with two new lines.

– Listing 11–13 on page 22 refers to "org.springframework.webflow.manager.
mvc.FlowController" The word "manager" needs to be replaced with the word "executor".

– The next paragragh on page 22 contains a reference to "org.springframework.webflow.mvc.FlowController". This should be "org.springframework.webflow.executor.mvc.FlowController".

– Page 26 refers to " org.springframework.webflow.config.FlowBuilder". This should be "org.springframework.webflow.builder.FlowBuilder".

Chapter 12

[global and specific changes]
– Page 8, first sentence contains " org.springframework.binding.AttributeMapper". Should be "org.springframework.binding.mapping.AttributeMapper".

– Page 9, first paragraph contains "ParameterizableFlowAttributeMapper", should be DefaultFlowAttributeMapper.

– Page 9, Listing 12–9 first method signature is "public Map createSubflowInput(Request…..". Should be "public AttributeMap createSubflowInput(Request….".
First line in first method is "Map map = new HashMap()" should be "AttributeMap map = new AttributeMap()".
Second method signature is "public void mapSubflowOuput(Map subflowOutput…." should be "public void mapSubflowOutput(UnmodifiableAttributeMap…".

– Page 12, In "Integration With Web Frameworks" the term FlowExecutionManager needs to be replaced with FlowExecutor. There are 5 occurences (although any others you spot should also be changed).

The last but one sentence "Both methods accept org…... and return org…." should read "Both methods accept org.springframework.webflow.ExternalContext in their parameters and return org.springframework.webflow.executor.ResponseInstruction , from which the org.springframework.webflow.ViewSelection can be obtained."

Listing 12–11 has completely changed:

public interface ExternalContext {

public String getContextPath();

public String getDispatcherPath();

public String getRequestPathInfo();

public ParameterMap getRequestParameterMap();

public AttributeMap getRequestMap();

public SharedAttributeMap getSessionMap();

public SharedAttributeMap getApplicationMap();

public interface SharedMap extends Map {

public Object getMutex();

}

public static class SharedAttributeMap extends AttributeMap {

public SharedAttributeMap(SharedMap sharedMap) {

super(sharedMap);

}

public SharedMap getSharedMap() {

return (SharedMap)getMapInternal();

}

public Object getMutex() {

return getSharedMap().getMutex();

}

}
}

– Page 13 Last entry in Table 12–2 contains the word "manager." should be "executor."

"The FlowExecutionManager" should be renamed "FlowExecutor".
Listing 12–12 heading should be changed to "org.springframework.webflow.executor.FlowExecutor".
Both methods return "ViewSelection". They should return "ResponseInstruction".
Within the Note, "FlowExecutionManager" should be renamed to "FlowExecutor".
The next two paragraphs require all instances of "FlowExecutionManager" to be changed to "FlowExecutor". I count 2 instances
The next two paragraphs require all instances of "_flowExecutionId" to be changed to "_flowExecutionKey". I count 2 instances
The "org.springframework.webflow.executor.support.FlowExecutionManagerParameterExtractor" needs to be "org.springframework.webflow.executor.FlowExecutorArgumentExtractor".

-Page 15, Listing 12–13 Please remove the last method "rehydrate".

Listing 12–14 FlowExecutionContext has changed. It essentially needs to be:

public interface FlowExecutionContext extends FlowExecutionStatistics {

public Flow getFlow();

public AttributeMap getScope();

FlowSession getActiveSession();
}

The next paragraph contains the phrase "the active flow definition, the current state, and" which needs to be replaced with "conversation scope and".

The next paragraph contains the phrase "The root flow" which needs to be replaced with "The flow". The last sentence contains "getActiveFlow()" which needs to be "getFlow()".

Page 17, Listing 12–15 has changed. It should now be:

public interface RequestContext {

public Flow getActiveFlow() throws IllegalStateException;

public State getCurrentState() throws IllegalStateException;

public AttributeMap getRequestScope();

public AttributeMap getFlowScope();

public AttributeMap getConversationScope();

public ParameterMap getRequestParameters();

public ExternalContext getExternalContext();

public FlowExecutionContext getFlowExecutionContext();

public Event getLastEvent();

public Transition getLastTransition();

public UnmodifiableAttributeMap getAttributes();

public void setAttributes(AttributeCollection attributes);

public UnmodifiableAttributeMap getModel();
}

Page 18 contains two references to "org.springframework.webflow.manager.ConditionalFlowExecutionListenerLoader". They should be "org.springframework.webflow.executor.ConditionalFlowExecutionListenerLoader ".

Listing 12–17 on Page 18 contains a reference to "org.springframework.webflow.manager.FlowExecutionManagerImpl". It should be "org.springframework.webflow.executor.FlowExecutorImpl".

Page 19, Listing 12–18 has completely changed:

public interface FlowExecutionRepository {

public FlowExecution createFlowExecution(String flowId);

public FlowExecutionKey generateKey(FlowExecution flowExecution) throws FlowExecutionRepositoryException;

public FlowExecutionKey generateKey(FlowExecution flowExecution, Serializable conversationId) throws FlowExecutionRepositoryException;

public ConversationLock getLock(Serializable conversationId);

public FlowExecution getFlowExecution(FlowExecutionKey key) throws FlowExecutionRepositoryException;

public void putFlowExecution(FlowExecutionKey key, FlowExecution flowExecution) throws FlowExecutionRepositoryException;

public FlowExecutionKey getCurrentFlowExecutionKey(Serializable conversationId) throws FlowExecutionRepositoryException;

public ViewSelection getCurrentViewSelection(Serializable conversationId) throws FlowExecutionRepositoryException;

public void setCurrentViewSelection(Serializable conversationId, ViewSelection viewSelection) throws FlowExecutionRepositoryException;

public void invalidateConversation(Serializable conversationId) throws FlowExecutionRepositoryException;
}

– Page 22 contains a number of references to FlowExecutionContinuationKey. This has been renamed to FlowExecutionKey.

– Page 22 contains a number of references to _flowExecutionId. This has been renamed to _flowExecutionKey.

– Page 22 at the bottom contains a reference to "org.springframework.webflow.execution.repository.SimpleFlowExecutionRepository ". It should be "org.springframework.webflow.execution.repository.support.SimpleFlowExecutionRepository".

Page 23. The note should read "This is the default implementation."

Page 23 contains a reference to "_flowExecutionId", it should be "_flowExecutionKey".

Page 24 contains two references to "_flowExecutionId", they should be "_flowExecutionKey".

Page 30, Table 12–10 contains a reference to "RedirectViewSelector". Should be "ExternalRedirectSelector".

Table 12–11 is wrong, should be:

ApplicationViewSelector If viewName is specified.
ApplicationViewSelector If redirect:viewName is specified.
ExternalRedirectSelector If externalRedirect:/url?par1=x is specified
FlowRedirectSelector If flowRedrect:/url is specified
YourViewSelector If bean=yourBean is specified.

– Page 31 contains three references to "FlowExecutionManagerParameterExtractor". They should all be "FlowExecutorArgumentExtractor".

– Page 31 contains three references to "FEMPE". They should all be "FEAE".

– Page 34 contains a reference to "InvalidConversionationContinuationException". Should be "CannotContinueConversationException".

: 21 Mar 2006 22:40 | Tags: Errata Expert MVC Spring Swf Webflow | Comments (10) | Close comments | Report a problem

March 16, 2006

Any decent, easy to use online backup clients out there?

I am looking for an online backup solution for my technically disadvantaged (I am being really unfair ;)) father in law.

Ideally it would transparently upload any modified documents automatically without any user intervention. Anything which requires him getting involved in the process isn’t really acceptable.

Any ideas? Less than 10/mnth would be good.

: 16 Mar 2006 15:04 | Comments (2) | Close comments | Report a problem

March 08, 2006

Oracle lameness and empty sets :(

So I wanted to run a query which would return a number of rows if their ids were in a set:


  select url from page where id in (....)

This works fine.

Unfortunately it breaks horribly if the set is empty. Why? There is no mathematical ambiguity about an empty set. Why would oracle simply not return 0 rows?

: 08 Mar 2006 12:13 | Comments (4) | Close comments | Report a problem