DDevelopment & Design

BigDecimal and Locale in Grails

I was recently puzzled by strange behaviour of Grails application with web service interface. It resulted with rounding currency amount values when I sent request from my browser but it worked perfectly if another client application sent same…

I was recently puzzled by strange behaviour of Grails application with web service interface. It resulted with rounding currency amount values when I sent request from my browser but it worked perfectly if another client application sent same request. After investigation it turned out that the HTTP requests were not exactly identical. The browser request contained header entry with Polish locale pl-PL for which coma is a decimal separator.

Request
http://localhost:8080/helloworld/amount/displayAmount?amount=12.22

Header
Accept-Language: pl-PL,pl;q=0.8,en-US;q=0.6,en;q=0.4

In order to reproduce this behaviour I created a simple Grails 2.1 HelloWorld app.

AccountController.groovy

package helloworld

class AmountController {

    def displayAmount(PaymentData paymentData) {
        render "Hello, this is your amount: " + paymentData.amount.toString()
    }
}

PaymentData.groovy:

    package helloworld

import grails.validation.Validateable

@Validateable
class PaymentData {
    BigDecimal amount

    static constraints = {
        amount(nullable: false, min: BigDecimal.ZERO, scale: 2)
    }
}

 

Starting this app we can observe rounding of cents in amount to 00 when sending request with dot in amount (http://localhost:8080/helloworld/amount/displayAmount?amount=12.22)


Whereas for amount with coma it gives a result with valid cent part (http://localhost:8080/helloworld/amount/displayAmount?amount=12,22)


Same behaviour might be expected in case of other locales that use coma as decimal separator, e.g. de_DE. Very not an obvious feature.

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Inconsistent Dependency Injection to domains with Grails

I've encountered strange behavior with a domain class in my project: services that should be injected were null. I've became suspicious as why is that? Services are injected properly in other domain classes so why this one is different?

Constructors experiment

I've created an experiment. I've created empty LibraryService that should be injected and Book domain class like this:

class Book {
    def libraryService

    String author
    String title
    int pageCount

    Book() {
        println("Finished constructor Book()")
    }

    Book(String author) {
        this()
        this.@author = author
        println("Finished constructor Book(String author)")
    }

    Book(String author, String title) {
        super()
        this.@author = author
        this.@title = title
        println("Finished constructor Book(String author, String title)")
    }

    Book(String author, String title, int pageCount) {
        this.@author = author
        this.@title = title
        this.@pageCount = pageCount
        println("Finished constructor Book(String author, String title, int pageCount)")
    }

    void logInjectedService() {
        println("    Service libraryService is injected? -> $libraryService")
    }
}
class LibraryService {
    def serviceMethod() {
    }
}

Book has 4 explicit constructors. I want to check which constructor is injecting dependecies. This is my method that constructs Book objects and I called it in controller: 

class BookController {
    def index() {
        constructAndExamineBooks()
    }

    static constructAndExamineBooks() {
        println("Started constructAndExamineBooks")
        Book book1 = new Book().logInjectedService()
        Book book2 = new Book("foo").logInjectedService()
        Book book3 = new Book("foo", 'bar').logInjectedService()
        Book book4 = new Book("foo", 'bar', 100).logInjectedService()
        Book book5 = new Book(author: "foo", title: 'bar')
        println("Finished constructor Book(Map params)")
        book5.logInjectedService()
    }
}

Analysis

Output looks like this:

Started constructAndExamineBooks
Finished constructor Book()
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2
Finished constructor Book()
Finished constructor Book(String author)
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2
Finished constructor Book(String author, String title)
    Service libraryService is injected? -> null
Finished constructor Book(String author, String title, int pageCount)
    Service libraryService is injected? -> null
Finished constructor Book()
Finished constructor Book(Map params)
    Service libraryService is injected? -> eu.spoonman.refaktor.LibraryService@2affcce2

What do we see?

  1. ✔

    Empty constructor injects dependencies.

  2. ✔

    Constructor that invokes empty constructor explicitly injects dependencies.

  3. ✘

    Constructor that invokes parent's constructor explicitly does not inject dependencies.

  4. ✘

    Constructor without any explicit call declared does not call empty constructor thus it does not inject dependencies.

  5. ✔

    Constructor provied by Grails with a map as a parameter invokes empty constructor and injects dependencies.

Conclusion

Always explicitily invoke empty constructor in your Grail domain classes to ensure Dependency Injection! I didn't know until today either!