MongoDB "NumberLong/$numberLong" issue while converting back to Java Object

Question

I am having a json which is somethink like {"Header" : {"name" : "TestData", "contactNumber" : 8019071740}}

If i insert this to mongoDB it will be something like

{"_id" : ObjectId("58b7e55097989619e4ddb0bb"),"Header" : {"name" : "TestData","contactNumber" : NumberLong(8019071743)}

When i read this data back and try to convert to java object using Gson it throws exception com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a long but was BEGIN_OBJECT at line 1 column 109 path $.Header.contactNumber

I have found this, But i was wondering if i have very complex json structure then i might need to manipulate many json nodes in this approach.

Do anyone has any better alternatives on this.

Edit:1 I am reading querying and converting json as below

Document MongoDocument = mycollection.find(searchCondition);
String resultJson =  MongoDocument.toJson();
Gson gson = new Gson();
Model model= gson.fromJson(resultJson, ItemList.class);

Solution 1

Take a look at: converting Document objects in MongoDB 3 to POJOS

I had the same problem. The workaround with com.mongodb.util.JSON.serialize(document) does the trick.

Solution 2

We can use below code:

Document doc = documentCursor.next();
JsonWriterSettings relaxed = JsonWriterSettings.builder().outputMode(JsonMode.RELAXED).build();
CustomeObject obj = gson.fromJson(doc.toJson(relaxed), CustomeObject.class);

Solution 3

Mongo db uses Bson format with its own types which follows json standards but it can't be parsed by json library without writing the custom wrapper/codec.

You can use third party framework/plugins to make the library take care of converting between document and pojo.

If that is not an option for you, you will have to do mapping yourself.

Document mongoDocument = mycollection.find(searchCondition);
Model model= new Model();
model.setProperty(mongoDocument.get("property");

Solution 4

Document.toJson() gives bson but not json.

I.e. for Long field myLong equals to xxx of Document it produces json like:

 "myLong" : { "$numberLong" : "xxx"}

Parsing of such with Gson will not give myLong=xxx evidently.

To convert Document to Pojo using Gson you may do next:

Gson gson = new Gson();
MyPojo pojo = gson.fromJson(gson.toJson(document), MyPojo.class);

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