convert composite java object to CSV

Question

I have an object, say Response.java that looks like the following:

class Response
{
   private User user;  // has firstName, lastName, age etc.
   private Address address; // has city, state, country etc.
   private OrderInfo orderInfo;  // has orderNumber, orderDate etc.

   // constuctors, getters/setters follow

}

I need to convert a List of these objects into csv, so my end goal is something like:

firstName, lastName, age, city, state, country, latitude, orderNumber, orderDate
john, doe, 25, dallas, tx, usa, somelat, 101, 08/17/2015
jane, doe, 21, atlant, ga, usa, somelat, 102, 08/15/2015

I tried to use two libraries - jackson (csv dataformat), org.json (JsonArray), but i couldn't get the desired result.

This is my jackson csv code:

Response response = getResponse();
final CsvMapper mapper = new CsvMapper();
final CsvSchema schema = mapper.schemaFor(Response.class);
final String csv = mapper.writer(schema).writeValueAsString(response);

With Jackson, i am getting

com.fasterxml.jackson.core.JsonGenerationException: CSV generator does not support Object values for properties

Is there a way to convert the composite object into csv in the way i need (just the fields without the json like grouping)?

Answer 1

So I ran similar code that you are using in a test project and it looks like you will need to use @JsonUnwrapped on all your objects (User, Address, and OrderInfo).

Jackson CSV doesn't support objects as properties which is why you got that exception. Here is the issue on Github: Jackson CSV Object properties issue

Here is sample code I used to verify this:

Test response = new Test();
response.setNum(1);
Stub s = new Stub();
s.setAge("12");
s.setName("Colin");
response.setS(s);
final CsvMapper mapper = new CsvMapper();
final CsvSchema schema = mapper.schemaFor(Test.class);
final String csv = mapper.writer(schema.withUseHeader(true)).writeValueAsString(response);
System.out.println(csv);

Output from the above code was the following:

num,age,name
1,12,Colin