Missing support for multiple yaml documents in a single file.

[hemanik]

yaml spec v1.2 contained information about files with multiple documents:
http://www.yaml.org/spec/1.2/spec.html

YAML uses three dashes (“---”) to separate directives from document content. This also serves to signal the start of a document if no directives are present. Three dots ( “...”) indicate the end of a document without starting a new one, for use in communication channels.

Example:

# Ranking of 1998 home runs
---
- Mark McGwire
- Sammy Sosa
- Ken Griffey

# Team ranking
---
- Chicago Cubs
- St Louis Cardinals

Example with ...:

---
time: 20:03:20
player: Sammy Sosa
action: strike (miss)
...
---
time: 20:03:47
player: Sammy Sosa
action: grand slam
...

The above-mentioned structures are not supported by object mapper at the moment.

[cowtowncoder]

Does not work in what sense?

Note that since they are separate logical documents, you can not read into a single value, but you can construct a MappingIterator for reading them as a sequence of values. Or, at low level, can use a YAMLParser so that each document is separated by null token to signal end of a logical document (and last indicated by 2 nulls).

So perhaps this could be usage issue.

[zcourts]

For those not familiar with MappingIterator or how to use it here's an example

YAMLFactory yaml;
ObjectMapper mapper;

YAMLParser yamlParser = yaml.createParser("file-with-multiple-docs.yaml")
List<ObjectNode> docs =
mapper
      .readValues[ObjectNode](yamlParser, new TypeReference[ObjectNode] {})
      .readAll();

[cowtowncoder]

@zcourts thank you for sharing this! Yes, that is the way (from Scala in this example?).

[teabot]

How does this work for serialisation?

[cowtowncoder]

@teabot You would use SequenceWriter, obtained via ObjectWriter, so you need to create ObjectWriter from mapper, then SequenceWriter with writeValues().

So something like

SequenceWriter sw = mapper.writer().writeValues(outputStream);

[piyushkumar13]

@cowtowncoder I am trying to serialize into multi docs, but not successful. Here is my code :

       File directory = new File("src/main/resources/output");
        String fileName = "output-multidocs.yaml";

        try(SequenceWriter sequenceWriter = mapper.writer().writeValues(new File(directory, fileName))){
            sequenceWriter.init(true);
            sequenceWriter.writeAll(detailsList); // detailsList is an arrayList of object. 
            sequenceWriter.writeAll(detailsList); // Expectation is this would create separate doc in the same yaml file. But it was appending to above list.

        }catch (Exception e){
            e.printStackTrace();
        }

[cowtowncoder]

@piyushkumar13 Could you please file a new issue with title of something like "Can not write multi-document YAML output" or something, with that example, ref to this issue?

Btw, that init() should NOT be needed or used. I assume it does not make difference.

[piyushkumar13]

@cowtowncoder Sure. will raise a separate issue. Thanks for replying.

[blacelle]

In order to manage documents with Array at the root (instead of Object as the common case), we went with ContainerNode instead of ObjectNode:

JsonParser yamlParser = objectMapper.getFactory().createParser(input);
List<ContainerNode> docs = objectMapper.readValues(yamlParser, ContainerNode.class).readAll(); 

[cowtowncoder]

Thank you @blacelle! I think nominal type JsonNode would also work and produce appropriate ArrayNode or ObjectNode.