Tapestry 5 web framework

Scot Mcphee — Wed, 26 Aug 2009 12:09:18 +0000

Lately I’ve been writing a Tapestry 5 based web application. I’ve used it before for a smaller application but this is the first time I’ve used it on a larger project. In a number of ways it is a very powerful framework to write web applications.

The basics of Tapestry is that it is a component-based web framework. Just about everything, including web pages, are components. Components may contain other components. The way it works is very simple and quite elegant, once you get used to it and weaned off the big-XML-file style of configuring a web application.

When you start, you have two main Java packages that are created for you (if you use the maven archetype, otherwise you will create these packages yourself). If your package root is say “net.crazymcphee.webapp”, then your two packages are “net.crazymcphee.webapp.pages” and “net.crazymcphee.webapp.components”. To configure a Tapestry 5 project with maven use this command and answer the prompts:

mvn archetype:generate \

    -DarchetypeCatalog=http://tapestry.formos.com/maven-snapshot-repository

Don’t use the one in the tutorial as it will not work! This is an excellent illustration of the first and most serious problem that Tapestry 5 has: the documentation not only has massive lacunas, it is also sometimes wrong and not updated.

Now, any class that you create in the “pages” package will automatically become a page in your application. But these classes need not be very complex at all. For example:

package net.crazymcphee.webapp.pages;
 
import java.util.Collections;
import java.util.List;
 
import org.apache.tapestry5.annotations.Persist;
import org.apache.tapestry5.annotations.Property;
import org.apache.tapestry5.ioc.annotations.Inject;
 
import net.crazymcphee.webapp.model.Person;
import net.crazymcphee.webapp.services.PersonService;
 
public class Persons {
 
    @Inject
    private PersonService personService;
    @Property
    @Persist
    private List persons;
    @Property
    @Persist
    private String searchTerm;
 
    Object onSubmitFromSearch() {
        persons = personService.findPersons(searchTerm);
        return this;
    }
 
    Object onSubmitFromClear() {
        persons = Collections.EMPTY_LIST;
        return this;
    }
 
}

You can see that this class doesn’t extend any infrastructure classes and has quite a simple structure. This is a fully functional page with two actions – one populates a list, the other clears it.

Now, to explain just a little here; PersonService is injected by Tapestry, but you need to configure in your AppModule which implementation you want to use. You can also use it with Spring as your IOC container but the one that comes with Tapestry is perfectly good enough for most applications.

The List, persons, and the searchTerm parameters are marked as @Property (so we don’t need to add getters and setters) and also @Persist so that the variables are preserved from request to request.

The methods “onSubmitFromSearch” and “onSubmitFromClear” are using a convention – “onSubmit” will also work, but assuming (as is true in this case) that we may have multiple forms on the one page, each method will only be fired from the “search” form in one instance, and the “clear” form in the other. These names are not special, it’s just (as you’ll see below) the forms will have these two names. They could be “Bill” and “Ben” in which case the methods would be “onSubmitFromBill” and “onSubmitFromBen”.

You will also note that these methods return the same page instance, which tells Tapestry to re-render the same page, but if you wanted to forward onto another page, you would add a instance variable, mark it with an @InjectPage annotation, and return that instance variable (after initialising it in your “onSubmit” method) instead of just returning “this”.

This page Persons, is available at {application-context-path}/persons. But there is one other part of the puzzle – the actual view. As mentioned, Tapestry uses convention over configuration and in this case, the convention is that the Page markup must be named the same: Persons.tml. Here is the matching tml file for the class above;

<html t:type=“layout” title=“Peoples I Might Know”

t:sidebarTitle=“Current Time”

xmlns:t=“http://tapestry.apache.org/schema/tapestry_5_1_0.xsd”

xmlns:p=“tapestry:parameter”>

, , etc. tags, comes from Layout.tml –>

<t:form t:id=“search”>

<t:textfield t:id=“searchTerm” validate=“required” size=“20″/>

<t:submit t:id=“searchPeople” value=“search”/>

t:form>

<t:grid source=“persons”/>

<t:form t:id=“clear”>

<t:submit t:id=“clearPeople” value=“clear”/>

t:form>

html>

Yes, it’s that bloody simple. The first form fires the “onSubmitFromSearch” method (with a little bit of validation, done in javascript) and the second method clears the list. In-between, there is this <t:grid source=“persons”/> business, which, if the ‘persons’ variable in the page class is populated, will show a list of its contents!

To test our app, we can use the command-line ‘mvn clean jetty:run’. When Jetty has run up, then we can point our browser at the web app: http://localhost:8080/sample-webapp/Persons, and with any luck we will see the following:

Now, by default, Tapestry creates the web app to use the template design as shown above. Of course, you can make it look completely some other way – or even use a totally different template if you want. The page template is just a component that’s included.

So if you enter in a search term and click the search button, you’d expect to see a result like this:

As you can see, the list is automatically populated with the details returned from the service method (in this particular instance, this are just a canned response, but normally of course they’d be the result of a database or a web service call of some type).

When you click the clear button, the list is cleared as you’d expect:

Now, here’s a really powerful feature I find in Tapestry. Let’s say our automated acceptance tests assert that when the ‘Clear’ button is pressed, the Search box as well as the persons list is cleared. What Tapestry allows us to to do, is keep Jetty running, edit the files in the IDE, and re-run the tests against the running app without restarting! We edit our method:

    Object onSubmitFromClear() {
        persons = Collections.EMPTY_LIST;
        searchTerm="";
        return this;
    }

In this case I’ve also added a bit of space around the clear button in the template as well:

And now our failing test will pass.

Editing files like this in the running web app only works for Pages and I think Components. If I had to change the service or model classes I’d have to restart, but “mvn jetty:run” isn’t very a heavyweight process.

As I said above, Tapestry’s not perfect: it’s major flaw is the poor documentation. Convention-over-configuration is easy to grok – if you know the convention. If you don’t and the documentation doesn’t tell you, and you can’t find a sample of what you need, it can be very frustrating. There is an excellent user list though.

Its other major flaw may be the stability of the API. Tapestry 5 is different (and incompatible) from Tapestry 4 is different from Tapestry 3. But so far I’ve used it on a couple of projects and I’m really enjoying it. I really hate the oodles of XML boilerplate and massive amounts of configuration found in Spring and I find myself somewhat reluctant to use it unless I really have to. Tapestry solves for me a range of different problems and mostly it presents a very elegant way to create a componentised web application. You might like to give it a try.

Attached is the sample code used above. It took me about 10 minutes to write (far shorter than it took me to write this blog entry!) - sample-webapp.tar bundle

JSR286 and vendor sales teams

Scot Mcphee — Sun, 25 Jan 2009 01:06:27 +0000

Eric Spiegelberg recently speculated that the new Java portal specification JSR286 was at the edge of irrelevance. And others agree. I think it’s worse than irrelevant – it’s a solution in search of a problem.

I’ve worked on a successful (JSR168) portal implementation, just last year. I truly don’t see what the concept of ‘portal’ brings to a web application beyond what could be simply programmed into a customised web application. We used Spring MVC Portal running under Websphere Portal and calling back-end services deployed on a BEA Weblogic server using Spring remoting (note: not WSRP which would have probably massively increased complexity). The reason this mix of platforms (Websphere and Weblogic) was used was political, not technical. I believe the whole use of portals in general tends to follow organisation’s political and not technical needs.

Despite all that, overall the custom portlets and the project as a whole was quite successful and the customer satisfied with the result. However I felt the most difficult aspects of the project were the parts of the deployment that were left to the portal container to provide. These are the things that are touted as the ‘advantage’ using a portal container over a simple custom-built web application. Content management features caused the team members delivering these enormous headaches (and late nights) and the same can be said of the authentication and authorisation mechanisms employed. I felt we could have easily delivered these components using known JEE development APIs with all the customisation required by the customer in at least an equal amount of time.

As a contrast, we used Tapestry 5 to develop (actually, completely rewrite from an earlier phase one version in dire need of improvement) an administration component as a straight web application deployed into the Weblogic server. This took a pair of us less than two weeks to write using a functional-test-driven approach and delivered a very nice web app.

The issue of portal containers and standards being a political rather than a technical concern is particularly pertinent to me at the moment because it looks likely in the near future I’ll be working on another portal implementation for another client. I can’t be more specific regarding this but this particular client had already bought the portal server from a vendor and then approached consultants in order to get an actual implementation completed. Of course, no requirements gathering or analysis was done to determine if the portal solution was indeed the right one – the vendor’s sales team effectively provided the assurances of product suitability. Because the money is already spent and reputations already staked on the portal platform there’s no possible way a better solution can be suggested by any technical expert at this stage.

In my view, that’s the “relevance” of portal servers in the Java world. Vendor sales teams love to sell them.

Update

Jakub Holý makes an excellent observation about validity of the concept of a portal server:

It’s a pity that portals and portlets aren’t easier to use and haven’t made it into the mainstream, the abilities of content aggregation, personalization, uniform security etc. are promising and as we can see in the rise of personal mashups like iGoogle, the fundamental ideas behind portals are still valid and extremely attractive. I hope that some mashup technology will soon provide a viable, light-weight alternative to portals.

That’s an important point: iGoogle is the most widely used example of a “portal” architecture. The modern trend towards the “mashup” (especially in social software) also shows the idea to aggregate different web applications under a common view, with security and other features is a valid one: it’s just the bloated, slow specification process, and predatory vendor sales departments that are stopping real innovation in this space in the Java area. Hopefully some light weight technology will soon emerge from among something like Spring, Tapestry, and GWT to produce a “portal” server that delivers actual value, and ease of development, deployment and usage, in a corporate context.

let x=x » tapestry5

Tapestry 5 web framework

JSR286 and vendor sales teams

Update