Thinking About Starting A Grails 3 Tutorial

I was at the Austin Groovy and Grails User Group this past week. The speaker was Ken Kousen. I am seeing a pattern with the No Fluff Just Stuff Speakers: they are all really smart guys who tell the same jokes year after year.

Ken Kousen said that he has run into some gotchas with Grails 3, and that the docs are not up to date. He said Grails 3 needs a book, and he doesn’t see one coming out any time soon. A lot of the Groovy and Grails authors either have just finished books and don’t want to go through the grinder again right away.

I have been thinking for a couple of years of making a Grails tutorial, sort of like a Hartl tutorial for Grails. Perhaps it is time to get it started. If I did this, it would only exist online.

I have also thought about making a quick Ratpack tutorial. It would be nice if there was a linear set of steps to make a CRUD app. It’s nice to know some theory, but sometimes I wish projects would make it easier to help newbies get through a “Hello, World”.

I have to think about it. I might be biting off more than I can chew.

You’re welcome.

Some Groovy Threading

There is an example of using threads with Groovy in Venkat’s book.

He uses the GDK extension to Thread and calls Thread.start. I wondered if the main thread would wait until the started thread completed, and what would happen if you started another thread.

I made some changes, and ran it.

Here is my class:

package info.shelfunit.venkat.ch07

class BetterThreadExample {
    
    def printThreadInfo( msg ) {
        println "$msg" 
    }
    
    def doStuff() {
        sleep( 5000 )
        printThreadInfo 'Main'
        println "Main is ${Thread.currentThread().name}"
        Thread.start {
            def name = Thread.currentThread().name
            printThreadInfo "AA Started: ${name}"
            sleep( 3000 ) 
            println "AA Interrupted 1" 
            sleep( 1000 )
            println "AA IN started"
            sleep( 3000 )
            println "AA still in started"
            println "AA Finished Started"
        }
        
        Thread.start( 'Second' ) {
            def name = Thread.currentThread().name
            printThreadInfo "BB Started Daemon: ${name}"
            sleep( 5000 ) 
            println "BB Interrupted 2" 
            sleep( 1000 )
            println "BB in second thread"
            sleep( 1000 )
            println "BB Finished Started Daemon"
        }
        println "At the end in main"
    }
      static void main( String[] args ) { 
          def bte = new BetterThreadExample()
          bte.doStuff()
      } // end method main

}

Here is the result:

Main
Main is main
At the end in main
AA Started: Thread-1
BB Started Daemon: Second
AA Interrupted 1
AA IN started
BB Interrupted 2
BB in second thread
BB Finished Started Daemon
AA still in started
AA Finished Started

 

So the main thread gets to its last statement pretty quickly. The two threads run simultaneously. I already knew this, but it’s good to review threads every now and then.

I was always intimidated by threading and concurrent  programming. Maybe it’s not too bad in Groovy.

You’re welcome.

2015-05-25 Tweets

Groovy Validator: Ready For Public Consumption

I think the Groovy Validators are ready for public consumption, at least as ready as they’ll ever be.

The basic idea is to allow you to use the same sort of constraints you get with Grails domain objects and use them in Groovy. The main difference is this uses annotations, and Grails uses static blocks.

I have tested them with POGOs, using final and mutable fields, and with immutable objects. Everything seems to work as intended.

Here is the README for the project:

This project has a few annotations that validate fields in POGOs, sort of like Grails constraints.

I will attempt to make some annotations for properties in Groovy.

Here is a POGO:

package info.shelfunit.properties.sample

class Book {

    int pages
    String title
    int year
}

It’s clean, and has no getters and setters. But what I do not like is there is no validation for your data. What if you want your String to be between 10 and 20 characters? What if you want your int field to be more than 100? And what’s to stop some dingo from trying to create a book object with less than 0 pages?

So I made some annotations that can do some validation for you.

package info.shelfunit.properties.sample

import validation.IntAnnotation
import validation.StringAnnotation

class Book {

    @IntAnnotation( minValue = 30, maxValue = 400, throwEx = false )
    def pages
    @StringAnnotation( minLength = 5, maxLength = 20, regEx = /^.*?[Gg]roovy.*$/  )
    String title
    int year
}

For POGOs, if a numeric field is declared as “def”, it will become null if the argument does not meet the validation constraints. If it is declared as a primitive, it will be set to 0 if the argument does not meet the validation constraints.

This project can also validate fields in immutable objects. In addition to using the annotations for the fields, you annotate the class with ImmutableValidator:

package info.shelfunit.properties.sample.immutable

import validation.ImmutableValidator
import validation.IntAnnotation
import validation.LongAnnotation
import validation.StringAnnotation

@ImmutableValidator
class ImmutableObject002 {
    @StringAnnotation( minLength = 5, maxLength = 10 )
    String firstString
    @IntAnnotation( minValue = 10, maxValue = 100 )
    int firstInt
    @LongAnnotation( maxValue = 100L, divisorSet = [ 5L, 7L ] )
    long firstLong
}

To process the annotations, put your properties in a Map, and add a boolean called “validation” and set it to true (since I couldn’t overload the Map constructor, I added a boolean):

def validatingImObject = new ImmutableObject002( 
    [ firstString: "Hi Again", firstInt: 11, firstLong: 22L ], true )

Adding the “throwEx” will throw an exception if the arguments do not meet the validation constraints. It is optional and is set to false by default. If an exception is thrown, it will print out the value and the constraints.

You might get a message like this:

"Hey" is a String with a length outside the range of 5 and 10 or does not match the regular expression ".*"

You can also use it with immutable objects annotated with the ImmutableValidator annotation. This would be a second boolean after the Map with your properties, since the first boolean controls validation:

def thirdImObject = new ImmutableObject002( 
[ firstString: "Hi Once Again", firstInt: 1234567, firstLong: 222L ], 
true, true )

In that case, you get a message with a line for each field. So you might get a message like this:

Groovy validation exception: 
"eeeeeeeeeee" is a String with a length outside the range of 5 to 10 characters or does not match the regular expression ".*" 
1234567 is an integer outside the range 10 to 100 or it is not divisible by anything in the set [1] 
222 is a long outside the range 0 to 100 or it is not divisible by anything in the set [5, 7]

If “throwException” is true for an immutable object and an exception is thrown, then the object will not be created.

This library can also handle final fields in mutable objects.

import groovy.transform.ToString
import validation.IntAnnotation
import validation.FinalFieldValidator

@ToString( includeNames = true )
@FinalFieldValidator
class Car {
    @IntAnnotation( minValue = 10, throwEx = false )
    int miles
    @IntAnnotation( minValue = 1990 )
    final int year
}

As with immutable validation, you need to use a map in the constructor to validate a final field.

def car = new Car( [ miles: 50, year: 2007 ], true, true )

Right now it only handles String, double, float, int and long. For String, it checks the string is checked against a minimum (“minLength”) and maximum (“maxLength”) length, and against a regular expression (“regEx”). For integers and longs, the field is checked against minimum (“minValue”) and maximum (“maxValue”) values, and a set of divisors (“divisorSet”). For double and float, the field is checked against minimum (“minValue”) and maximum (“maxValue”) values. There are defaults for all of these.

To use this project: Run

gradle distZip

and use build/libs/groovy-validator.jar in your project.
You’re welcome.

Setting Final Fields In Groovy Validators

There is another update in Groovy Validators. I think I figured out how to get them to work to validate/constrain final fields in mutable objects.

Here is an object:

import groovy.transform.ToString
import validation.IntAnnotation
import validation.FinalFieldValidator

@ToString( includeNames = true )
@FinalFieldValidator
class Car {

    @IntAnnotation( minValue = 10, throwEx = false )
    int miles
    @IntAnnotation( minValue = 1990 )
    final int year
}

You can validate the final field (and the other one as well) by instantiating the object with a map for the fields, and a boolean to trigger the FinalFieldValidator annotation:

def car = new Car( [ miles: 50, year: 2008 ], true )

I am still working on the Spock tests. I hope to have things wrapped up this weekend.

You’re welcome.

Hidden Annotation in Groovy Validators

There is another update to the Groovy Validators. (I know I keep saying I am done, but like The Godfather, I keep getting pulled back in.)

I made a new annotation @Hidden. Here is the summary from the groovydoc:

The purpose of this annotation is to help you keep your private fields private.

Suppose you have a field in an object you want to change. In that case, making it final will not work. But you also do not want code outside the object to change it. Making it private won’t work in Groovy either. You could write a setter that takes an argument and does nothing with it, over and over. Or you could use this annotation.

Here is an example on how to use it:

It is said you are only as old as you feel. Suppose going on a yoga retreat helps you feel a year younger, but visiting your in-laws makes you feel a year older. (One way to avoid this is to not marry a Scala programmer.)

class AgeHolder
    @Hidden
    int perceivedAge
    
    AgeHolder( argAge ) {
        this.perceivedAge = argAge
    }
    
    def visitYogaRetreat() {
        perceivedAge--
    }
    
    def visitInLaws() {
        perceivedAge++
    }
}

You’re welcome.

 

2015-04-20 Tweets

Taking a Break From Groovy Validators

I worked a bit on my Groovy Validator project.

I was trying to process the annotation in a class referenced by GroovyASTTransformationClass. I thought that there were a couple of ways it could be done, but none of them seemed to work. I was actually able to create the setter in the class, I inserted a static initializer that called my current annotation transformer that works at runtime, but neither seemed to work.

I plan on moving on to other things for the time being. I might ask for some help on the Groovy mailing list, but if I do, I will have to formulate a coherent request. I asked for help on the list a while back, and I think I included too much detail because I never got a response.

You’re welcome.