I recently developed a Grails plugin which provides support for easily accessing Clojure code in a Grails app. The details of how the plugin works are covered at http://grails.org/plugin/clojure. That page includes a link to a brief video demonstration which is available at http://s3.amazonaws.com/jeffscreencasts/grails_clojure_demo.mov. Check it out.
Shortly after publishing the plugin I posted something about it on Twitter. Not too long after that a couple of other SpringSource folks tweeted about Clojure (here and here). I got a couple of questions (in jest I am sure) about SpringSource and Clojure. "Is SpringSource Moving To Clojure?". Of course not. SpringSource is not moving to Clojure. SpringSource is all about helping folks build serious applications for the JVM and most of that is done in Java. This is not news. I work on Groovy and Grails. Much of what I do is in Groovy. This too is not news. Making it easy for folks to use languages like Scala and Clojure while taking advantage of all the great stuff that Grails has to offer, that is appealing to me and that is why I developed the Clojure plugin.
Clojure is a really interesting language. There are others. The fact that 3 folks from SpringSource have expressed some kind of interest in Clojure shouldn't be all that surprising. There are probably even more folks at SpringSource who have some kind of interest in Clojure but for entertainment, lets focus on the 3 mentioned...
I am honestly not sure how many technologists work for SpringSource but for the sake of having a number to work with, lets say there are 50. Lets also say that Clojure is interesting enough that 15% of JVM developers are interested in learning more about it. I can't back that number up with any research, lets just go with it. If 15% of JVM developers are interested in the language and you take a random group of 50 JVM developers (the 50 in question are certainly not 50 random developers, these are the edge cutters which probably makes them more likely to be interested in keeping an eye on what is new, but work with the idea that they are random)... Do the math. No, really... Do the math. Do the math to figure out the likelihood that 3 of the 50 would be interested in Clojure. I challenge you to do the math in Clojure and post your solution in a comment here. Do it in Scala, Do it in Groovy. Pick a JVM language and do the math.
The simplest solution is probably not very interesting. Prefer a solution that shows off something interesting in your language of choice.
Hmmm... are you more likely to need to refer to the Clojure book, or the high school math book? ;)
Now, you have one more reason to tinker with a new language.
Enjoy.
Grails, SpringSource And Clojure Thursday, July 30, 2009
Grails 1.1 beta3 Is Out! Thursday, January 29, 2009
We are closing in on the much anticipated release of Grails 1.1. Today beta 3 was released. See the release notes.
A new feature that has not been documented yet involves new validation capabilities. Up to this point, domain classes and command objects within a Grails app have supported really powerful validation capabilities. See section 7 in The User Guide for info on how that works. What is new is now you can apply those same validation capabilities to any class within a Grails app, not just domain classes and command objects. Making a class validateable involves defining a static property called "constraints" and assigning a closure, just like you would in a domain class or a command object.
Second, you have to tell Grails about your validateable class. You have 2 options for doing that. One option is to mark you class with the org.codehaus.groovy.grails.validation.Validateable annotation. Another option is to define your validateable classes in grails-app/conf/Config.groovy by assigning a value to the grails.validateable.classes property. That would look something like this...
grails.validateable.classes = [ com.mycompany.dto.SomeClass, com.mycompany.SomeOtherClass]
An annotated class might look something like this...
// src/groovy/com/companyname/SomeClass.groovy
package com.companyname
import org.codehaus.groovy.grails.validation.Validateable
@Validateable
class SomeClass {
Integer age
String name
static constraints = {
age range: 16..66
name blank: false, size: 5..35
}
}
Note that if you are using the annotation based approach, Grails will search all classes in the app to find all of the @Validateables. While that isn't really a performance problem, you can tune that a bit by specifying some specific packages that Grails should search. To do that, assign a value to grails.validateable.packages in grails-app/conf/Config.groovy like this...
grails.validateable.packages = ['com.companyname.dto', 'com.companyname.someotherpackage']
If the grails.validateable.packages property has a value then Grails will only look in those packages (and packages below those packages) for classes marked with @Validateable.
While this is still beta software, I think the feature will end up being delivered in the final release pretty much like it is described above. If you have any input on that or any other features in Grails. We would love to hear from you. Bring it to the mailing list or file a JIRA issue.
Enjoy!
Getting Groovy With "with" Thursday, November 13, 2008
UPDATE 12/15/2008: I committed a change yesterday that changes the behavior of the .with method to use DELEGATE_FIRST as the resolveStrategy instead of OWNER_FIRST. If you are not sure what that means, you should by the end of this post.
Strange enough title.
Let's start with a hypothetical conversation between a geeky developer and his much less geeky wife:
Jeff: Betsy, how are you?
Betsy: I am fine thanks. How are you?
Jeff: Betsy, I am fine thank you.
Betsy: Great.
Jeff: Betsy, you know my birthday is the day after tomorrow right?
Betsy: Yes, I haven't forgotten. You mention it about 9 times a day you know.
Jeff: Betsy, yes I know. Are we going to have an ice cream cake?
Betsy: Yes, I think that would be good.
Jeff: Betsy, are you going to buy me the new Opeth DVD?
Betsy: I will get it for you but that music sucks big time.
Jeff: Betsy, that is awesome. Thank you.
Betsy: Why do you keep saying "Betsy" at the beginning of every sentence?
Jeff: Betsy, I guess I am used to inflexible languages which aren't very expressive.
Um, what does any of that have to do with Groovy? Well, lets talk about the problem with this conversation (aside from the lady's lack of appreciation for Swedish heavy metal). What is wrong is Jeff begins each sentence with "Betsy". Why might he do that? One reason is so Betsy knows that he is talking to her. Clearly this isn't necessary. It isn't necessary because she already knows he is talking to her. A context has been established which makes the addressing unnecessary. Jeff began the conversation by addressing Betsy, they probably made eye contact and were in close proximity. Once the conversation started, there isn't much question about who each sentence is being directed to.
Again, what does any of that have to do with Groovy? Lets press on...
Consider the following Java code which prints out a specific date.
// PrintIndependenceDay.java
import java.util.Calendar;
import java.util.Date;
public class PrintIndependenceDay {
public static void main(String[] args) {
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.set(Calendar.MONTH, Calendar.JULY);
calendar.set(Calendar.DATE, 4);
calendar.set(Calendar.YEAR, 1776);
Date time = calendar.getTime();
System.out.println(time);
}
}
Groovy developers can look at that and find quite a bit of noise that doesn't really have anything to do with what the code is trying to do but I want to focus on one specific thing. That one thing is all of the interaction with the calendar variable. Notice that we call clear() on the calendar, then call set() several times and later call getTime() on that same variable. All of those calls are prefixed with "calendar." so the compiler knows what we want to do. If we called "clear()" instead of "calendar.clear()", what would that mean? Are we calling the clear() method in this class? If that was our intent, it would not work because there is no clear() method. We have to prefix the call with an object reference so the compiler knows where to send the request. That seems to make sense. However, if we are going to do a bunch of things "with" the same object, wouldn't it be kind of nice if we could somehow do all of those things without all the repetition. Specifically, it might be nice if we could get rid of all of those "calendar." prefixes.
On to Groovy...
The following Groovy code does the same thing that the Java code above does.
// PrintIndependenceDay.groovy
def calendar = Calendar.instance
calendar.with {
clear()
set MONTH, JULY
set DATE, 4
set YEAR, 1776
println time
}
Wow. That is a good bit cleaner than what we started with. Part of the reason for that is we were able to get rid of all of those "calendar." prefixes. What allowed us to do that is calling the "with" method on the calendar object and passing a closure as an argument. What we have done there is establish a context that says "do all of this stuff with this calendar object". When the closure executes, the calendar is given an opportunity to respond to method calls like clear() and set() and the implicit call to getTime() when referring to the "time" property which is being passed to println. Likewise, the references to MONTH, JULY, DATE and YEAR properties are also being handled by the calendar object.
That is pretty slick. Lets dig just a little deeper to get a little better understanding of what is really going on.
Groovy closures have a delegate associated with them. The delegate is given an opportunity to respond to method calls which happen inside of the closure. Here is a simple example:
// define a closure
def myClosure = {
// call a method that does not exist
append 'Jeff'
append ' was here.'
}
// assign a delegate to the closure
def sb = new StringBuffer()
myClosure.delegate = sb
// execute the closure
myClosure()
assert 'Jeff was here.' == sb.toString()
When the closure is executed, those calls to append() in the closure end up being sent to the delegate, the StringBuffer in this case.
Something similar is happening in the Groovy calendar code above. A closure is being passed to the with() method. That closure is calling methods like set() and getTime() which don't really exist in that context. The reason those calls don't fail is the with() method is assigning a delegate to the closure before it is executed. The delegate being assigned is the object that the with() method was invoked on. In the calendar example, the delegate is the calendar object. Something like this is happening...
def closure = {
clear()
set MONTH, JULY
set DATE, 4
set YEAR, 1776
println time
}
def calendar = Calendar.instance
closure.delegate = calendar
closure()
This code does the same thing as the first Groovy example. Obviously the first one is cleaner.
I sort of lied a bit, or at least left out a detail that may be significant. The closure that is being passed to the with() method is really being cloned and it is the clone that is assigned the delegate and executed. This is a safer approach than monkeying with the original closure. If the reasons for that aren't clear, the explanation is another story.
Another bit of info that is missing here is the strategy that a closure uses to decide when to send method calls to the delegate. Each Groovy closure has a resolveStrategy associated with it. This property determines how/if the delegate comes in to play. The 4 possible values for the resolveStrategy are OWNER_FIRST, DELEGATE_FIRST, OWNER_ONLY and DELEGATE_ONLY (all constants defined in groovy.lang.Closure). The default is OWNER_FIRST. Consider the owner to be the "this" wherever the closure is defined. Here is a simple example...
class ResolutionTest {
def append(arg) {
println "you called the append method and passed ${arg}"
}
def doIt() {
def closure = {
append 'Jeff was here.'
}
def buffer = new StringBuffer()
closure.delegate = buffer
// the append method in this ResolutionTest
// will be called because resolveStrategy is
// OWNER_FIRST (the default)
closure()
// give the delegate first crack at method
// calls made inside the closure
closure.resolveStrategy = Closure.DELEGATE_FIRST
// the append method on buffer will
// be called because the delegate gets
// first crack at the call to append()
closure()
}
static void main(String[] a) {
new ResolutionTest().doIt()
}
}
So you see how the with() method helps establish a context where a bunch of things may happen "with" a specific object without having to refer to that object over and over. This can help clean up code like the Java code we started with. This approach can also be really useful when building a domain specific language in Groovy, a topic for another time.
Enjoy! :)
Grails Training In Chicago Monday, August 04, 2008
We are really excited to have a 3 day Groovy/Grails training event coming up in Chicago later this month. The training dates are August 26-28. The training will be held at the Hotel Indigo in Palatine.
This is 3 days of lecture and reinforcing lab work. Attendees should expect to write a lot of Groovy and Grails code with your training expert. There is no better way to quickly get your team up to speed on the technology, well beyond the basics.
As with all G2One training events, students will receive a free 12 month license to use IntelliJ IDEA. The IntelliJ guys have done a fantastic job of building first class Groovy and Grails support for the IDE.
For a full course outline and more information, please visit http://g2one.com/training/. Any questions may be directed to training@g2one.com.
G2One QuickCast Site Launched! Wednesday, July 30, 2008
G2One have launched the G2One QuickCast site. A G2One QuickCast is fast and furious little movie demonstrating something interesting about the Groovy language and/or the Grails framework.
The first movie available there demonstrates how powerful tools like Grails and Git can work together to support a really really agile development process. Watch this movie and try to do something like this with your web framework and your VCS. If you can't, your tools are not flexible enough. :)
Enjoy!
G2One Groovy Grails Training In North America Monday, July 14, 2008
G2One have announced our Groovy/Grails North American public training schedule for the rest of the year. The schedule is available at http://www.g2one.com/training/.
Our training events are a fantastic experience. G2One are the folks who lead and sustain the development of both Groovy and Grails. No one understands the technology better than the people who build it. G2One training events give developers an opportunity to spend several days with a technology expert covering everything from fundamentals to advanced language and framework features. The sessions include a perfect mix of lecture and reinforcing lab work. That hands on approach is a great way for developers to internalize the details. There is no better way to quickly get a team up and running with the technology.
Grails Plugin For Hudson Thursday, June 19, 2008
I am pleased to announce that we have worked up a Grails plugin for Hudson. Hudson is a really slick continuous integration server. Check out their site for more info on the engine itself.
It has always been possible to build Grails apps from Hudson but in the past this has involved writing shell scripts that are triggered by Hudson. This works but is not the slickest solution. What you really want is for the CI server to have knowledge of the fact that the project you are building is a Grails app and that knowledge will allow the tool to be more efficient about carrying out the build and also allow the CI server to provide Grails specific options for the build. This is where the new Grails plugin is heading.
Right now the plugin is very basic. In the system configuration screen you may configure as many Grails installations as you like. This is useful for situations where the same CI server may be building multiple projects with different version of Grails or maybe even building multiple copies of the same project with multiple versions of Grails. Below is a screenshot of the system configuration screen:
Notice that there is built in validation to make sure you have entered a valid path to your Grails installation.
When configuring a project in Hudson you have a lot of options for what should happen at build time. The Grails plugin adds a "Build With Grails" option and if that option is selected you can select from a list of common build targets to execute as well as type in any arbitrary targets you may want to execute. This is useful for executing Grails commands that are not in the list of checkboxes and for executing your own custom Grail scripts that may be part of your project. Below is a screenshot of the project configuration screen:
The first version of the plugin has not been released yet but will be soon. In the meantime, I would be happy to hear what kinds of capabilities you would like to see the plugin provide. Even in its current very basic state, the plugin is very useful as it makes configuring a Grails project in Hudson drop dead simple.
