Question

I’ve defined a simple Xtext grammar which looks like this (simplified):

grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals
generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"
import "http://www.eclipse.org/emf/2002/Ecore" as ecore

System:
   'Define System'
   (
     'Define Components' '{' components+=Component+ '}'
   )
   'End'
;

Component:
    'Component' name=ID 'Value' value=Double ';'
;

Double returns ecore::EDouble:
    '-'? INT? '.' INT
;

The problem I like to solve is – how can I convert a simple Java Object to a valid xtext file?

To simplify my problem, lets say we create a list of components in Java:

List<Component> components = new ArrayList<Component>();
components.add(new Component("FirstComponent", 1.0));
components.add(new Component("SecondComponent", 2.0));
components.add(new Component("ThirdComponent", 3.0));

The output-file I like to create should look like this:

Define System
   Define Components { 
       Component FirstComponent Value 1.0;
       Component SecondComponent Value 2.0;
       Component ThirdComponent Value 3.0;
   }
End

It is important that this file is checked by the xtext grammar, so that it’s valid.
I Hope you have any ideas for me. Here are some of mine, but so far I don’t know how to implement them:

Idea #1:
I know how to read and write a file. In my head one solution could look like this:
I have the list in my Java code, now I like to write a file which looks like the output-file above. Afterwards I like to read this file and check for errors by the grammar. How can I do this?

Idea #2:
If I imagine I would create a xml file out of Java code using JDOM, I wish I could do the same in xtext. Just define a parent “Define System” which ends with “End” (see my output-file) and then add a child “Define Components {” which ends with “}” and then add the children to this, e.g. “Component FirstComponent Value 1.0;”. I hope this isn’t confusing 🙂

Idea #3:
I could use a template like the following and add children between the braces “{” … “}”:

Define System
   Define Components { ... }
End

Btw: I already tried Linking Xtext with StringTemplate code generator, but it is kind of another problem. Hope you have any ideas.

Answer 1

You can use Xtext’s serialization for this. Unlike Java’s default Serialization API, Xtext’s implementation creates the DSL.

The code would look like so:

Injector injector = Guice.createInjector(new  my.dsl.MyDslRuntimeModule());  
Serializer serializer = injector.getInstance(Serializer.class);  
String s = serializer.serialize(eobj);  

where eobj is an instance of System.

If you have written a formatter for your DSL, the output will also look nice.

Related blog post: Implement toString with Xtext’s Serializer