Seam


A Guide to Spigot For Seam Developers

Note : Spigot has been renamed to DataValve.

(Edit : I renamed this post so it doesn’t seem like Spigot is just for Seam, Spigot can be used with different frameworks or without any at all. However, I wrote this post since Spigot is so familiar to the Seam EntityQuery that it should be easy for Seam users to get the idea)

Seam developers should become familiar with Spigot concepts fairly quickly since they are very similar to those found in the Seam EntityQuery which was one of the main inspirations for the framework. If you imagine taking the entity query class and splitting it in two, one part to keep hold of state and the other to actually fetch the data. The stateful part is the Paginator that keeps track of what the current ordering of the data is, what is the current page and how big the pages are. The stateless part takes the Ejbql and the pagination information and returns a subset of the data. Now imaging that the data provider has the JPA pieces taken out and replaced with an abstract fetchResults method. This method is implemented in subclasses for specific data providers for text files, sql queries, jpa queries, native jpa queries, xml files, comma delimited or just an in memory dataset.
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Spigot 0.9.CR1 released

Note : Spigot has been renamed to DataValve and is hosted over on FlutterCode.com.

It’s been a while since I’ve posted anything new as I’ve been busy with a new Open Source software project called Spigot. It’s a java library that sits between your application code and your data sources (Hibernate, JPA, JDBC or any arbitrary source of data) and helps with things like pagination and sorting using a common interface so you can switch out data providers and use alternatives.

For query language data providers, Spigot also facilitates excluding restrictions from WHERE clauses when parameters are resolved to null. Parameters are handled using parameter resolvers so there is more than one way to parameterize the query including EL expressions, reflection or a value map on the data provider.

Spigot also provides a few other add-ins like converting any dataset into an in-memory dataset that can itself be paginated and sorted and shared across an application (such as commonly used data in a web application). The IndexedDataProviderCache can give you random access into a dataset with caching and look ahead loading. This lets you hook a dataset with thousands of rows up to a Swing JTable with an instant response and a very small memory footprint since it doesn’t need to load all the objects at once as the provider will load the records as needed and cache the results. This is demonstrated in the Swing Demo in the download. There are also demos for Wicket and CDI with JSF.

You can ready about why I created Spigot in the documentation

Spigot is currently hosted on Project Kenai, where you can download the release, view documentation online or read about 10 ways Spigot helps developers.

Understanding Nested Conversations

I had a bit of epiphany on the subject of nested conversations the other day when I was thinking about them and thought I’d share. I think nested conversations have been a little misunderstood with people unsure of how to use them, myself included, but I think I have found the best way to think of them.
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Seam is Dead, Long live Seam

With Weld 1.0, the reference implementation of JSR 299 – Java Contexts and Dependency Injection now released, attention at JBoss has no doubt turned to Seam 3 which is going to be built on top of Weld. Red Hat and JBoss are committed to returning innovations back the JCP as is the case with Seam which not only resulted in JSR 299, but has also influenced a number of other JSRs especially JSF 2. With JSR 299 standardizing the Seam ‘style’ of development it also brings about a some fundamental game changes for Seam 3 (hence the title) as much of the strength of Seam becomes part of the JEE standards.
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Conversational Pitfalls

Seam conversations have certain rules that you need to be aware of when using them. This article came about because for the last couple of years, the same questions have been asked on the Seam forums regarding conversations. It is also a couple of issues that cropped up while I was working on the Seam vs. Spring Web Flow articles. Some of the problems are uncannily similar with similar solutions, so parts of this series may be of interest to non-Seam users. Additionally, it seems like a lot of this stuff will also apply to the conversational pieces of JSR 299 – Contexts and Dependency Injection which will be a part of JEE 6.
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Logging Conversation Demarcation In Seam

One way to see where your conversations start and end is to use the Seam event model to observe the conversation start and ends.

@Name("conversationListener")
@Scope(STATELESS)
public class ConversationListenerBean implements ConversationListener {

	@Logger
	private Log log;
	
	@In
	private Conversation conversation;

	@Observer(value="org.jboss.seam.beginConversation")
	public void observeConversationStart() {
		log.debug("Conversation #0 Started",conversation.getId());		
	}
	
	@Observer(value="org.jboss.seam.endConversation")
	public void observeConversationEnd() {
		log.debug("Conversation #0 Ended",conversation.getId());
		
	}
}

Just add this bean into your project and it will automatically log when you start and end conversations.

Notes On Choosing A Web Framework

I’m looking at starting a new project and once again find myself choosing between frameworks. Having spent some time evaluating different ones I wrote up some notes to share and get some feedback that might alter my thoughts or opinions. Here’s the criteria I’m using to choose a framework in no particular order.
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