Vita Rara: A Life Uncommon

Programming

Creating a Struts 2 Action in Groovy


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(N.B.: For the latest on Struts 2 and Groovy see: Groovy Works)

Actions in Struts 2 are POJO's. Actions also serve the same purpose of the ActionForm from Struts 1, storing all of the data submitted by your user. Additionally Struts 2 action classes store the information you wish to display back to your user. (NB: Struts 2 also supports a ModelDriven style, where the Action does not need to store this data, but the ideas are largely the same.)

Over the course of developing a Struts 2 application you will write a lot of accessors, setThis(String in), getThat(). Personally I'm sick of writing those methods. Yes, I know Eclipse could write them for me, but I don't like Eclipse, and I haven't taken the time to learn another IDE. I like my Unix shell, maven, screen and vi (vim), thank you very much.

Gettin' Groovy With It


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Well, this week after hearing about Groovy and reading a bit about it I decided to take the plunge. I've grown tired of the get's and set's in Java code. It's all boiler plate repetitive, non-expressive junk. I've been listening to the Java Posse for quite some time, and all the talk about language level support of properties got to me. I checked out the Grooy Beans page and was sold.

As a proof of concept I started out writing some integration tests first. I used that as the test bed to get Groovy working with Maven. (I'll write more about that later.) Once I had that done I converted a Struts 2 Action that employed an Action class, a Model and a Query bean (to store the users input) into a single clear concise Groovy class. Three classes became one, rose in readability and it was quick. My Action, Model and Query class had a total of about 40 setters and getters. They're all gone now.

Web Page Data Models: Where do they go?


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You have a web page that has tabular data that doesn't represent simple rows from a database. It's a field from this table, one from that, one from four joins away. It's a little bit of data from all over your data model, but the client wants it on the screen. What do you do?

In the past I used to just a SQL result set and turn it into a Collection. Nice and neat. Iterate over the collection and put the stuff onto the screen. Simple enough, back then. Now I'd like to have better control over my models, and have them be full classes, with strong typing, setters and getters, etc.

The question is where should that class reside? Is it part of the data model? Is it a business object? It's really a presentation model. It only exists to make presentation of data easier. In essence it's like a report, or an element of a report. So, where should it live?

Creating a UI Component in Struts 2


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Problem

You have a form "element" that consists of several HTML actual elements. You'd like to create these using one Struts 2 UI tag, rather then write the HTML out everywhere it's needed.

Background

The Struts 2 UI tag library provide a component tag, which can be used to create your own "tags" without needing to dive into the JSP tag library API. Creating a tag using the Struts 2 component tag, also allows it to directly take advantage of the Struts 2 framework, such as OGNL support, and the existing Struts 2 UI tag themes.

Recipe

In this recipe we will creating an HTML control using the component tag that will display two input fields. This is a simple example, but it will show the process of creating a component, and tying it into the existing Struts 2 Xhtml theme.

Creating a Theme in Struts 2


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Struts 2 has a very powerful set of user interface tags (UI Tags). These tags are tightly integrated with the framework, taking full advantage of things like the OGNL Value Stack. The power this gives to a user it tremendous.

Struts 2 UI Tags

The Struts 2 UI Tags are backed with templates that do the actual rendering of HTML. You can change them without any need to touch the implementing classes. As of Struts 2.0.2 these templates are written in the FreeMarker template language. A quick look at the Freemarker Manual will provide you a quick overview of the language, and is helpful if you have questions about the language. Anyone familiar with JSP, PHP, or other template languages can quickly grasp it.

Using a Conversation Scope in Struts 2


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What is a conversation scope?

A conversation scope fits between a Session scope and a Request scope in J2EE terms. An object in a session is specific to a particular user of a web app. If you place an object in the users session it will be available on every page hit the user makes.

A conversation scope defines a long lived set of data that is specific to a process, such as configuring a product, or filling out a customers personal and credit information. It differs from a session scope in that one user should be able to have multiple of th same type of conversation at the same time. You might actually have to help more than one customer at a time, or configure multiple products, one on each tab in your web browser.

Mark's Struts 2 Cookbook


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Struts 2 is the new version of Struts, under development at the Apache Group. It is based on WebWork 2, and has many modern web framework features, like user interface tags, type conversion, and validation. Struts 2 is highly flexible and extensible.

In this cookbook you will find HOWTO guides, and recipes for common scenarios in Struts 2.

Updating a List of Domain Entities in Struts 2


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I've been working on Quadran a lot, and I'm creating pages for editing lists of entities. The CRUD example from the Struts 2 Showcase application does this in a very simple manner. It recreates all of the entities every time you update the list. That's fine for an example but unusable in real life.

In real life we have to present entities from our database and then put the values back into the same entities, and update our database. We can't just re-create them.

The Entity

So, we'll start with a simple domain object and assume that we're using something like JPA or Hibernate to persist it via a Data Access Object (DAO), and that it contains a property called "id".

Don't Swallow Exceptions


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Over the past two days I've been trouble shooting an application for a client. It's an old Java server application based on the Enhydra Framework and EJB 1.1. It's old.

I had most everything working but something in the system was throwing an exception that the code was swallowing and just display a page that said an exception had been thrown. No log message, no stack trace, nothing. Don't ever do this. If you don't have a system wide means of handling exceptions at least put in an e.printStackTrace(). It's the least you can do.

Eventually we had to go to the vendor, who no longer really supports the application, and have them add the e.printStackTrace() statement so we could debug the application. One line was all it took to fix the issue.

JBoss 4, EJB 3 Entities (JPA), and Spring


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Over the last week or so I have been working on getting JBoss, JPA and Spring working together. When I wrote my previous entry I thought I had everything working. Well, up to that point I had not tried to save a record to the database. When I tried to do that nothing happened. This lead to a long debugging process that felt more like a hopeless goose chase at times. With the help of Costin Leau on the Spring forum I finally got it working, but it was quite the trial. Not many people have attempted to get this combination working. One of the things that complicated my setup is that my data access objects are a descendant of the JpaDaoSupport class provided in the Spring framework.

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