Writing JAXB in Groovy

byDominik Przybysz
September 6, 2015
2 minute read

Suppose you want write a jaxb class in groovy. Why? Because you do not have to write these all getters, setters and other methods. You only have to write your fields down.@XmlRootElement@HashCodeAndEquals@ToStringclass Person { String firstName String …

Suppose you want write a jaxb class in groovy. Why? Because you do not have to write these all getters, setters and other methods. You only have to write your fields down.

@XmlRootElement 
@HashCodeAndEquals 
@ToString 
class Person {
    String firstName String lastName Integer age
}

Lets check if we could unmarshal xml to Person class:

def 'should unmarshall person xml to object'(){
    given:
        JAXBContext jc = JAXBContext.newInstance(Person)
        String xml = 'JohnSmith20' 
    expect:
        jc.createUnmarshaller().unmarshal(new StringReader(xml)) == new Person(firstName: 'John', lastName: 'Smith', age: 20)
}

When we try this, then we obtain an eception:

com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions
groovy.lang.MetaClass is an interface, and JAXB can't handle interfaces.
 this problem is related to the following location:
  at groovy.lang.MetaClass
  at public groovy.lang.MetaClass com.blogspot.przybyszd.jaxbingroovy.Person.getMetaClass()
  at com.blogspot.przybyszd.jaxbingroovy.Person

 at com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException$Builder.check(IllegalAnnotationsException.java:91)
 at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.getTypeInfoSet(JAXBContextImpl.java:445)
 at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.(JAXBContextImpl.java:277)
 at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl.(JAXBContextImpl.java:124)
 at com.sun.xml.internal.bind.v2.runtime.JAXBContextImpl$JAXBContextBuilder.build(JAXBContextImpl.java:1123)
 at com.sun.xml.internal.bind.v2.ContextFactory.createContext(ContextFactory.java:147)
 at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:247)
 at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:234)
 at javax.xml.bind.ContextFinder.find(ContextFinder.java:462)
 at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:641)
 at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:584)
 at com.blogspot.przybyszd.jaxbingroovy.PersonJaxbTest.should unmarshall person xml to object(PersonJaxbTest.groovy:10)

It is because groovy defines getMetaClass method for us. Marshaller and Unmarshaller use by default

XmlAccessType.PUBLIC_MEMBER what means that public getters and setters should be used during marshalling/unmarshalling. To solve this just add XmlAccessorType annotatnio with XmlAccessType.FIELD on jaxb class:

@XmlRootElement @EqualsAndHashCode @XmlAccessorType(XmlAccessType.FIELD) class Person {
    String firstName String lastName Integer age
}

Of course if you want to apply this rule for each jaxb class in package, then you could put XmlAccessorType in pacakge-info.java file.

@XmlAccessorType(XmlAccessType.FIELD) package com.blogspot.przybyszd.jaxbingroovy;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;

Great, it works. Now let’s check out marshaller:

def 'should marshall person'() {
    given:
        JAXBContext jc = JAXBContext.newInstance(Person)
        Person p = new Person(firstName: 'John', lastName: 'Smith', age: 20)
        StringWriter sw = new StringWriter()
    when:
        jc.createMarshaller().marshal(p, sw)
    then:
        String xml = sw.toString()
        GPathResult gPathResult = new XmlSlurper().parseText(xml)
        gPathResult.name() == 'person'
        gPathResult.firstName == 'John'
        gPathResult.lastName == 'Smith'
        gPathResult.age == '20'
}

And it also works. Source is available here.

Dominik Przybysz

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DDevelopment & Design

Inconsistent Dependency Injection to domains with Grails

byTomasz Kalkosiński
October 18, 2012

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?

✔
Empty constructor injects dependencies.
✔
Constructor that invokes empty constructor explicitly injects dependencies.
✘
Constructor that invokes parent's constructor explicitly does not inject dependencies.
✘
Constructor without any explicit call declared does not call empty constructor thus it does not inject dependencies.
✔
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!