Jackson JSON Deserialization: array elements in each line

Question

I am using Jackson and would like to pretty-print JSON such that each element in arrays goes to each line, like:

{
  \"foo\" : \"bar\",
  \"blah\" : [
    1,
             


        

Answer 1

Mapper can be configured (jackson-2.6) with:

ObjectMapper mapper = ...
DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultIndenter.SYSTEM_LINEFEED_INSTANCE);
mapper.setDefaultPrettyPrinter(prettyPrinter);

//use mapper 

Answer 2

If you don't want to extend DefaultPrettyPrinter you can also just set the indentArraysWith property externally:

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.INDENT_OUTPUT);

DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultIndenter.SYSTEM_LINEFEED_INSTANCE);

String json = objectMapper.writer(prettyPrinter).writeValueAsString(object);

Answer 3

Thanks to the helpful hints, I was able to configure my ObjectMapper with desired indentation as follows:

private static class PrettyPrinter extends DefaultPrettyPrinter {
    public static final PrettyPrinter instance = new PrettyPrinter();

    public PrettyPrinter() {
        _arrayIndenter = Lf2SpacesIndenter.instance;
    }
}

private static class Factory extends JsonFactory {
    @Override
    protected JsonGenerator _createGenerator(Writer out, IOContext ctxt) throws IOException {
        return super._createGenerator(out, ctxt).setPrettyPrinter(PrettyPrinter.instance);
    }
}

{
    ObjectMapper mapper = new ObjectMapper(new Factory());
    mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
}

Answer 4

try out JSON Generator...

API Reference
good example

Answer 5

The answer thankfully provided by OP shows a way for obtain a single-array-element-per-line formatted JSON String from writeValueAsString. Based on it here a solution to write the same formatted JSON directly to a file with writeValue with less code:

private static class PrettyPrinter extends DefaultPrettyPrinter {
    public static final PrettyPrinter instance = new PrettyPrinter();

    public PrettyPrinter() {
        _arrayIndenter = Lf2SpacesIndenter.instance;
    }
}

{
    ObjectMapper mapper = new ObjectMapper();
    ObjectWriter writer = mapper.writer(PrettyPrinter.instance);
    writer.writeValue(destFile, objectToSerialize);
}

Answer 6

You could extend the DefaultPrettyPrinter and override the methods beforeArrayValues(…) and writeArrayValueSeparator(…) to archieve the desired behaviour. Afterwards you have to add your new Implementation to your JsonGenerator via setPrettyPrinter(…).