[FIXED] Convert POJO into JSON

Issue

I have a POJO.

@Data
@AllArgsConstructor
@Builder
public class Emp {
    private String name;
    private String position;
}

Suppose, we have created an object

Emp emp = new Emp("Manager", "Bob");

How can I convert it to a list and save it in a database in JSON format?

The data should be stored in the database in the format below:

{
  list:[
    {
       position: Manager
       name: Bob
    }
  ]
}

Are there any ready solutions for that?

I converted an object into a list and then I called the .toString() method on it:

Collections.singletonList(emp);

But when I store it in the database, the next save goes to the database:

[Emp(position=Manager, name=Bob)]

But I need to store the record in a different way

Solution

How can I convert it to a list and save it in a database in JSON format?

The data should be stored in the database in the format below:

{
  "list": [
    {
       "position": "Manager"
       "name": "Bob"
    }
  ]
}

Since the serialized JSON is required to have a property "list" you can't simply serialize the List as is.

Instead, you can define a POJO wrapping this list.

That's how it might look like (I've made it generic in order to make it suitable for serializing any type of list):

@Data
@AllArgsConstructor
public static class ListWrapper<T> {
    private List<T> list;
}

And that's how it can be serialized using Jackson's ObjectMapper and ObjectWriter:

List<Emp> emps = List.of(new Emp("Manager", "Bob"));
ListWrapper<Emp> listWrapper = new ListWrapper<>(emps);
        
ObjectMapper mapper = new ObjectMapper();
ObjectWriter writer = mapper.writerWithDefaultPrettyPrinter();
        
String json = writer.writeValueAsString(listWrapper);
System.out.println(json);

Output:

{
  "list" : [ {
    "name" : "Manager",
    "position" : "Bob"
  } ]
}

Answered By - Alexander Ivanchenko
Answer Checked By - David Goodson (JavaFixing Volunteer)