Spring Boot Java map Entity to DTO: array literal (strings) INSTEAD of array of objects - spring

Question

sample get request: http://localhost:3000/contact/1
What I got:
{
"id": 1,
"firstname": "First Name",
"lastname": "Last Name",
"emailaddresses": [
{
"emailaddress": "email#gmail.com"
},
{
"emailaddress": "email#g.c"
}
]
}
What I want:
{
"id": 1,
"firstname": "First Name",
"lastname": "Last Name",
"emailaddresses": ["email#gmail.com","email#g.c"]
}
The code below:
PersonDto
public class PersonDto {
private Long id;
private String firstname;
private String lastname;
private List<EmailAddressDto> emailaddresses;
//getters setters
}
EmailAddressDto
public class EmailAddressDto {
private String emailaddress;
//getters and setters
}
the Service class
public PersonDto getPerson(Long personId) { //this is the method inside the class
Optional<PersonEntity> p = peopleRepository.findById(personId);
var dto = modelMapper.map(p.get(), PersonDto.class);
return dto;
}
I also have a PersonEntity class mapped one-to-many to an EmailAddressesEntity class.
I'm really new to spring/java - I couldn't figure out how to get the JSON structure I want.

Answer 1

You can just annotate emailaddress field of EmailAddressDto with #JsonValue and leave everything as is.
public class EmailAddressDto {
#JsonValue
private String emailaddress;
//getters and setters
}
Using the above the output of a sample:
PersonDto personDto = new PersonDto();
personDto.setId(1L);
personDto.setFirstname("John");
personDto.setLastname("Doe");
personDto.setEmailaddresses(Arrays.asList(new EmailAddressDto("john#doe.com"), new EmailAddressDto("foo#bar.com")));
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(personDto);
System.out.println(json);
is:
{"id":1,"firstname":"John","lastname":"Doe","emailaddresses":["john#doe.com","foo#bar.com"]}

Answer 2

I'd suggest that you use a List of Strings instead of a List of EmailAddressDto's.
Following reasons:
Since you only have one attribute in your Dto, you can easily just directly use a List of Strings instead.
You get the second JSON-Layout as a response to your GET-Request.
When using variant number 1 (with the List of EmailAddressDto), you will achieve a JSON-Response with multiple objects for your different E-Mail addresses.
Otherwise when you use variant number 2 (with the List of String), you will achieve a JSON-Response which looks like what you want to have.
So don't forget to change your entities aswell.
public class PersonDto {
private Long id;
private String firstname;
private String lastname;
private List<String> emailAddresses;
//getters setters
}

Answer 3

If you can change your PersonDto that would be the easiest and cleanest way to do it.
public class PersonDto {
private Long id;
private String firstname;
private String lastname;
private List<String> emailaddresses;
//getters setters
}
While mapping your entities you would need to map EmailAddressesEntity to a String representing it (emailaddress).
If this is not possible you will need a custom converter for EmailAddressDto as follows:
public class ListEmailAddressDtoConverter extends StdConverter<List<EmailAddressDto>, List<String>> {
#Override
public List<String> convert(List<EmailAddressDto> emailAddresses) {
return emailAddresses.stream().map(EmailAddressDto::getEmailaddress).collect(Collectors.toList());
}
}
Then you need to tell Jackson to use it:
public class PersonDto {
private Long id;
private String firstname;
private String lastname;
#JsonSerialize(converter = ListEmailAddressDtoConverter.class)
private List<EmailAddressDto> emailaddresses;
//getters setters
}