stack man stack man - 1 month ago 4x
Java Question

Can´t create entity in MongoDB

I am brand new to MongoDB, so sorry if the question is basic.

I am trying to get a basic CRUD working with Java basic objects (POJOs), but this code fails. (What is the correct way of doing this? I think it might be close to this):

BasicDBObject document = new BasicDBObject();
document.put("name", user);

This is the message I am getting:

Exception in thread "main" java.lang.IllegalArgumentException: can't serialize class entities.users.NormalUser
at org.bson.BasicBSONEncoder._putObjectField(
at org.bson.BasicBSONEncoder.putObject(
at org.bson.BasicBSONEncoder.putObject(
at com.mongodb.DefaultDBEncoder.writeObject(
at com.mongodb.OutMessage.putObject(
at com.mongodb.DBApiLayer$MyCollection.insert(
at com.mongodb.DBApiLayer$MyCollection.insert(
at com.mongodb.DBCollection.insert(
at com.mongodb.DBCollection.insert(
at com.mongodb.DBCollection.insert(
at repositories.UsersRepository.createUser(
at repositories.UsersRepository.main(
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(
at sun.reflect.DelegatingMethodAccessorImpl.invoke(
at java.lang.reflect.Method.invoke(
at com.intellij.rt.execution.application.AppMain.main(


Here is the detailed analysis on this issue:-

Looks like "lombok" library adds the boilerplate code (i.e. getter and setter methods for the attributes) during compilation time. I have observed two behaviors while executing the program.

1) Eclipse behavior:-

When I run the program via IDE (e.g. eclipse), the "getter" and "setter" methods were not getting generated. I have got serialization error when I ran the main class. I have decompiled the classes User and NormalUser and checked the content. It doesn't have the "getter" and "setter" methods.

Online Java Decompiler

2) Maven behavior:-

I have used maven commands to build the project and checked the classes User and NormalUser. This time I can see the boilerplate codes being generated. I have executed my Main class and it worked fine.


MongoClient client = new MongoClient();
        MongoDatabase database = client.getDatabase("localhost");
        MongoCollection<Document> normalUserCollection = database.getCollection("normaluser");

        User normalUser = new NormalUser("jack", "mike", "US", "dni", "123", Gender.MALE);

        Document document = new Document();
        document.put("user", document.parse(new ObjectMapper().writeValueAsString(normalUser)));

Mongo Java Driver used:-



The document has been inserted successfully in MongoDB collection.

    "_id" : ObjectId("57d2e4134c1c7b287cde1d30"),
    "user" : {
        "surname" : "mike",
        "address" : "US",
        "dni" : "dni",
        "bankAccount" : "123",
        "admin" : false,
        "name" : "jack",
        "gender" : "MALE"