JSON.parse() equivalent in mongo driver 3.x for Java

Question

JSON.parse() from mongo (Java driver) returns either a BasicDBList or a BasicDBObject.

However, when migrating to mongo driver 3.x, what's the new parse method that returns either Document or List<Document>?

In the new driver, Document.parse() only parses an object, not an array (throws an exception when given an array).

What is the equivalent of JSON.parse() for Arrays with 3.x Java drivers ?

Broussard

I am facing the same issue, did you get any clean solution to this? – Regime

Answer 1

A simple trick to parse any JSON and to get either Document or List<Document>:

Document.parse("{\"json\":" + json + "}").get("json")

Eyrir

Answer 2

To parse JSON string data using the mongodb java driver 3.x:

Parse JSON document:

Use the Document.parse() static method to parse a single JSON document.

Document doc = Document.parse("{\"objA\":{\"foo\":1}}");

Parse JSON array:

Use an instance of BsonArrayCodec to decode a JsonReader.

For example:

final String JSON_DATA
    = "[{\"objA\":{\"foo\":1}},"
    + "{\"objB\":{\"bar\":2}}]";

final CodecRegistry codecRegistry = CodecRegistries.fromProviders(asList(new ValueCodecProvider(),
    new BsonValueCodecProvider(),
    new DocumentCodecProvider()));

JsonReader reader = new JsonReader(JSON_DATA);
BsonArrayCodec arrayReader = new BsonArrayCodec(codecRegistry);

BsonArray docArray = arrayReader.decode(reader, DecoderContext.builder().build());

for (BsonValue doc : docArray.getValues()) {
    System.out.println(doc);
}

ref: http://api.mongodb.org/java/3.2/org/bson/json/JsonReader.html, http://api.mongodb.org/java/3.2/org/bson/codecs/BsonArrayCodec.html

Corwun

Why not to just use BsonArray.parse then? – Laminous

Answer 3

Added cast to @Oleg Nitz answer, for completeness.

Object object = Document.parse("{\"json\":" + jsonData.getJson() + "}").get("json");

if (object instanceof ArrayList) {
    documents = (ArrayList<Document>) object;
} else (object instanceof Document) {
    document = (Document) object;
}

Housebreaking

Answer 4

How about this:

Document doc = new Document("array", JSON.parse("[ 100, 500, 300, 200, 400 ]", new JSONCallback()));
System.out.println(doc.toJson()); //prints { "array" : [100, 500, 300, 200, 400] }

Elwood

If you do a doc.get("array"), it'll return a BasicDBList, instead of a List :( – Broussard

True, but it is subclass of ArrayList. So you could do this: new Document("array", new ArrayList((List)JSON.parse("[ 100, 500, 300, 200, 400 ]", new JSONCallback()))); or use toMap(): BasicDBList bDBl1 = (BasicDBList) JSON.parse("[ 100, 500, 300, 200, 400 ]", new JSONCallback()); new Document("array", bDBl1.toMap()); – Elwood

It is possible we are missing something as this is not very clean – Elwood

That wouldn't work either because, if my array consisted of documents, it would be parsed as BasicDBObject, and not a Document. – Broussard

I agree, we're missing something crucial here. – Broussard

Answer 5

You're right that there's no easy equivalent.

If you use line-delimited JSON documents instead of a JSON array, it becomes fairly straightforward:

List<Document> getDocumentsFromLineDelimitedJson(final String lineDelimitedJson) {
    BufferedReader stringReader = new BufferedReader(
          new StringReader(lineDelimitedJson));
    List<Document> documents = new ArrayList<>();
    String json;
    try {
        while ((json = stringReader.readLine()) != null) {
            documents.add(Document.parse(json));
        }
    } catch (IOException e) {
        // ignore, can't happen with a StringReader
    }
    return documents;
}

For example, this call

System.out.println(getDocumentsFromLineDelimitedJson("{a : 1}\n{a : 2}\n{a : 3}"));

will print:

[Document{{a=1}}, Document{{a=2}}, Document{{a=3}}]

Tombouctou

This is rarely the case though, isn't it? – Broussard

It depends. This is the format output by mongoexport by default, for example. And there are several standardization efforts: JSON lines and ndjson – Tombouctou

I was referring to line separated JSON. Mostly, you've got objects in an array, which is the value to another key in another object altogether. – Broussard

Answer 6

The easiest equivalent for me is to use any json library to convert the json to POJO. Below is an example using jackson:

String input = "[{\"objA\":{\"foo\":1}},{\"objB\":{\"bar\":2}}]";
ObjectMapper mapper = new ObjectMapper();
List<Document> output = (List<Document>) mapper.readValue(input, List.class)
            .stream().map(listItem -> new Document((LinkedHashMap)listItem))
            .collect(Collectors.toList());

Hoisch

This doesn't handle nested objects, a map inside of your top level map. – Mousey