How to parse a bson.Document

Question

I have a java code that retrieves a bson.Document from MongoDB. An example JSON/BSON document is:

{
    "field1": "text1",
    "field2": {
        "field2Sub1": "text2"
    }
}

In my java code I manipulate it like this to get values of field1 and field2Sub1

com.fasterxml.jackson.databind.ObjectMapper objectMapper;

org.bson.Document documentFromMongo = this.getDocumentFromMongo();
org.bson.Document field2Document = documentFromMongo.get("field2", Document.class);

String field1Value = objectMapper.convertValue(documentFromMongo.get("field1"), String.class);
String field2Sub1Value = objectMapper.convertValue(field2Document.get("field2Sub1"), String.class);

Is there any way or some library or method I can use to get the value of field2Sub1 like this way:

String field1Value = objectMapper.convertValue(documentFromMongo.get("field2.field2Sub1"), String.class);

Answer 1

I don't know of another library doing this, but you could use org.bson.Document provided functionality to achieve similar effect. It's quite simple

1. Split your input/path by dot
2. Use Document.getEmbedded()

Like so:

public class MongoMain {

    private static final String JSON = "{\n" +
            "    \"field1\": \"text1\",\n" +
            "    \"field2\": {\n" +
            "        \"field2Sub1\": \"text2\"\n" +
            "    }\n" +
            "}";

    public static void main(String[] args) {
        Document document = Document.parse(JSON);
        String path = "field2.field2Sub1";
        String value = extractValue(document, path);
        System.out.println("extracted value - " + value);
    }

    private static String extractValue(Document document, String dotNotationPath) {
        List<String> path = Arrays.asList(dotNotationPath.split("\\."));
        return document.getEmbedded(path, String.class);
    }
}

The extractValue method does the trick - first split by dot and build a list, because getEmbedded accepts a list, then getEmbedded handles the rest.