Darwin's Theories - seam tag

Site Modernization

Thu, 26 Mar 2009 14:49:00 GMT

Every web site needs to keep improving, and your obd't servant is no different. I started almost exactly a year ago by replacing the old blog software with Pebble. Then I got busy with real work, and had to put aside site maintenance. Around the beginning of this year I was able to modernize both the home page of darwinsys.com (making it new and graphical) and the layout of the rest of the main site. This week, I re-did the Java Web Frameworks site, which has gone from coyote-ugly to fairly modern looking, after being re-implemented using the Seam framework. So, I am now running Seam ("war deployment" option) on Tomcat in production.

At the same time, I had to upgrade the Tomcat web server from 5.5 to 6.0, which went fairly smoothly, although there may be a few little bits that need a boost.

Using Java enums properly in Seam

Tue, 27 Jan 2009 22:22:00 GMT

The Seam documentation covers this now, but it's a bit short of complete examples. Most of this probably applies to other JSF/JPA deployments too (but please don't ask me how). To make the list of a given enum's values available to the view, just add one new annotated method to a "Factories" class.

@Name("factories")
public class Factories {

@Factory("countries")
public Country[] getCountries() {
   return Country.values();
    }

Because you want to display a user-friendly name in the web form, but store a short and consistent name in the database, the enum must have a "label" or "name" field and a getter method (many enums already do). For example, we'll display Canada in the drop-down but enter the ISO-3166 country code CA in the database.

/** See ISO-3166 */
public enum Country {
   CA("Canada"),
   US("United States"),
   AF("Afghanistan"),
   ...
   ;
   private String longName;
   private Country(String longName) {
       this.longName = longName;
   }
   public String getLongName() {
       return longName;
   }
   @Override
   public String toString () {
       return getLongName();
   }

You typically want to save the string name rather than the ordinal value into the database (especially with Countries where the list order will change in future as countries split or join!) the @Entity class must be annotated thusly:

   @Column(name="Country")
   @Enumerated(EnumType.STRING)   // default and only other choice is ORDINAL
   public Country getCountry() {
       return this.country;
   }

Then, to select it (display a drop-down), you'd use, for example:

      <h:selectOneMenu value="#{register.personalAddress.country}">
             <s:selectItems var="country" value="#{countries}"
                        label="#{country.longName}" noSelectionLabel="-- Select --"/>
              <s:convertEnum/>
       </h:selectOneMenu>

If you've used another framework than Seam, there's a bit of Seam's beauty: the Seam convertEnum tag fixes the 'orrible mess of having your data classes be required to know about UIComponent (can nobody on the JSF standards committee spell "tier violation"?).

To display the current value in a view-only page, you just need, for example,

<h:outputText id="country"
      value="#{person.personalAddress.country.longName}"/ >

The data must be basically spotless for the enum converter to work, so - if you didn't have enumerating check constraints on the database from day one - you may e.g., have to "sanitize" the data a little to ensure there are no non-null but blank values in the database, or convert any lower-case values to upper case to match the enum constants. If not you'll get strange message like the famous "can't find resultList" - always check the JBoss console log for a stack trace!

These can be cleaned with SQL like this, using whatever tool you use to feed raw SQL into whatever database you're using:

   update address set country = 'CA' where country = ''
Or you could set these values to NULL.

   update address set country = upper(country)

To check the values, you can use SQL similar to this:

    select distinct(country) from address

Then it all works nicely, as it should, without any need for EntityConverter or for mixing UIComponents into your data layer. Seam rocks!

Seam Leaves Home (on good terms)

Tue, 25 Mar 2008 00:58:00 GMT

In addition to cranking out a new stable release (2.0.1.GA) and a new early access release (2.1.0.A1), The JBoss Seam framework has been renamed to "The Seam Framework" and has a new website, http://www.seamframework.org/. This represents a "growing up" of sorts, similar to e.g., Jakarta Tomcat becoming Apache Tomcat, and differentiates Seam from the many smaller projects that are also part of JBoss - see the new diagram at http://labs.jboss.org/projects/, and note that Seam is right there at the top of the web tier. While still funded by RedHat/JBoss, with this new domain Seam is obviously being positioned to compete head-on with similarly-named project The Spring Framework.

As part of "moving out", Seam has been given a new logo, see http://www.seamframework.org/Community/GetASeamIcon. This is used in their new web site, which is of course running on Seam and available as part of the downloads (http://www.seamframework.org/Download). Speaking of downloads, if you're using a version older than 2.0.1.GA, now would be a good time to download and upgrade.

Also, there is a new book about Seam, Seam In Action (http://www.amazon.com/gp/product/1933988401), which you can now buy in Early Access (http://www.manning.com/dallen/) - you get EA PDF's now and the final version when it's released, and optionally a paper copy then too.

Finally, JBoss Tools - the all-encompassing Eclipse tools for developing Seam and Hibernate projects - has been upgraded to 2.0.1.GA. You might want to download this as well.