Loading an ArrayList<SomeType> with yaml.load()

[Jay Jay Billings]

I have a YAML file that has blocks similar to the sequence below:

- name: myName

  description: my Description

- name: otherName

  description : other Description

- name: thirdName

  description : third Description

I have created a Java Bean class that represents something like this, let's call it the Name class which has name and description as attributes. What is the best way to load this sequence into an ArrayList<Name> instead of an ArrayList<Map>? Calling yaml.load(input) loads the former and yaml.loadAs(input, Name.class) fails because it is a sequence.

Thanks,

Jay Jay Billings

[Jordan Angold]

If you use tags to tell SnakeYAML what type those maps are, then they will be loaded as that type. For example:

- !!some.package.Name

  name: myName

  description: my description

- !!some.package.Name

  name: otherName

  description: other description

...

That's the easiest way. You could probably achieve the same result in other ways, but it's not nearly as easy.

You may find it best to define tags for package names, especially if they are very long:

%TAG !pkg! tag:yaml.org,2002:some.package.

- !pkg!Name

  name: my name

  description: my description

...

Good luck,

/Jordan

[Jay Jay Billings]

Thanks, Jordan. Unfortunately the file I am parsing is generated by a third party and does not have tags. It is a 1MB file, so putting them in by hand is out too.

Jay

-----
Jay Jay Billings
Computational Scientist
Oak Ridge National Laboratory
Twitter Handle: @jayjaybillings

--
You received this message because you are subscribed to the Google Groups "SnakeYAML" group.
To unsubscribe from this group and stop receiving emails from it, send an email to snakeyaml-cor...@googlegroups.com.
To post to this group, send email to snakeya...@googlegroups.com.
Visit this group at http://groups.google.com/group/snakeyaml-core?hl=en.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

[Jordan Angold]

That's unfortunate.

In that case, you have two main options:

1) Write a loop to build instances of Name from the Maps that SnakeYAML gives you.

2) Extend org.yaml.snakeyaml.constructor.Constructor to follow the particular rules of your document.

I feel like option (1) is much easier to execute. It's unfortunate, but SnakeYAML can't do the whole job automatically.

/Jordan

[Andrey Somov]

Just for clarification.
The YAML dicument can be very flexible:

- name: myName

  description: my Description

- 3

- name: thirdName

  description : third Description

- 5: myName

  description: my Description

- name: otherName

- name: thirdName

  description : third Description

As you can see the parser must be prepared to receive any structure. The second option recommended by Jordan basically allows to choose at runtime (dynamically) the tag for data structure.

But the usecase is valid: it would be nice to extend the API to add an option to parse a sequence of JavaBeans

Cheers,
Andrey

[Jay Jay Billings]

Thanks Jordan. I implemented #1 on Sunday, but was just hoping for there to be an automated way similar to the way JAXB handles XML. Thanks again for your help!

-----
Jay Jay Billings
Computational Scientist
Oak Ridge National Laboratory
Twitter Handle: @jayjaybillings

[Jay Jay Billings]

Andrey,

Yes, I think it would be nice. I think it might be as simple as adding an operation like yaml.loadSequenceAs(InputStream,Class) where the second argument is used to state the type of each element in the sequence generically. This would return ArrayList<T> instead of ArrayList<Map>.

Jay

--
You received this message because you are subscribed to the Google Groups "SnakeYAML" group.
To unsubscribe from this group and stop receiving emails from it, send an email to snakeyaml-cor...@googlegroups.com.
To post to this group, send email to snakeya...@googlegroups.com.
Visit this group at http://groups.google.com/group/snakeyaml-core?hl=en.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

--

Jay Jay Billings

[Andrey Somov]

Developing general API is more complex. How to treat the corner cases ?

What shall happen if one document is different ? Exception ? Ignore ? Call special (user provided) code ?

Andrey

[Jay Jay Billings]

I would go with exception...

-----
Jay Jay Billings
Computational Scientist

Oak Ridge National Laboratory
Twitter Handle: @jayjaybillings