Spring Boot: Dynamically Ignore Fields While Serializing Java Objects to JSON

Let's say that we have a UserController class with two GET endpoints:

• /users/{id} endpoint, which returns a User object for a given id
• /users endpoint, which returns List<User>

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public class User {

    private Integer id;

    private String name;

    private Date dateOfBirth;

    private String city;

    // constructors, getters & setters are ignored

}

@RestController

public class UserController {

    @Autowired

    UserService userService;

    @RequestMapping(value = "/user/{id}", method= RequestMethod.GET)

    User getUser(@PathVariable("id") String id){

        return userService.getUser(id);

    }

    @RequestMapping(value = "/users", method= RequestMethod.GET)

    List<User> getAllUsers(){

        return userService.getAllUsers();

    }

}

Our client wants the id and name of all users in a JSON List when the /users endpoint is called. For the /users/{id} endpoint, they want the name, dateOfBirth, and city for the given user id.

If we use the User POJO class for both the endpoints, we will get the id, name, dateOfBirth, and city all the time. So we have to figure out a way to ignore fields at the time of serialization.

The Jackson library provides two annotations: @JsonIgnore and @JsonIgnoreProperties to ignore fields while serializing Java Objects to JSON. But both these annotations need the fields at compile time itself.

But in our case, the fields to be ignored have to be decided at the runtime, based on the endpoint called.

However, we can use MappingJacksonValue to ignore fields dynamically.

Here is a sample implementation:

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public class User {

    private Integer id;

    private String name;

    private Date dateOfBirth;

    private String city;

    // constructors, getters & setters are ignored

}

@RestController

public class UserController {

     @Autowired

    UserService userService;

    @RequestMapping(value = "/user/{id}", method= RequestMethod.GET)

    MappingJacksonValue getUser(@PathVariable("id") String id){

        SimpleBeanPropertyFilter simpleBeanPropertyFilter =

                SimpleBeanPropertyFilter.serializeAllExcept("id");

        FilterProvider filterProvider = new SimpleFilterProvider()

                .addFilter("userFilter", simpleBeanPropertyFilter);

        User user = userService.getUser(id);

        MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(user);

        mappingJacksonValue.setFilters(filterProvider);

        return mappingJacksonValue;

    }

    @RequestMapping(value = "/users", method= RequestMethod.GET)

    MappingJacksonValue getAllUsers(){

         SimpleBeanPropertyFilter simpleBeanPropertyFilter =

                SimpleBeanPropertyFilter.serializeAllExcept("dateOfBirth", "city");

        FilterProvider filterProvider = new SimpleFilterProvider()

                .addFilter("userFilter", simpleBeanPropertyFilter);

        List<User> userList = userService.getAllUsers();

        MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(userList);

        mappingJacksonValue.setFilters(filterProvider);

        return mappingJacksonValue;

    }

}

Explanation:

• Add the JsonFilter annotation on the POJO class

@JsonFilter("userFilter")

• Pass the name of the fields to be ignored to the serializeAllExcept method from the SimpleBeanPropertyFilter class

SimpleBeanPropertyFilter.serializeAllExcept("dateOfBirth", "city") - will ignore dateOfBirth & city fields

• Pass the JsonFilter name and SimpleBeanPropertyFilter object to the addFilter method

FilterProvider filterProvider = new SimpleFilterProvider().addFilter("userFilter", simpleBeanPropertyFilter);

• Pass the instance of the POJO and filter class to the MappingJacksonValue class

MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(userList);

mappingJacksonValue.setFilters(filterProvider);

• Make sure MappingJacksonValue is the return type of the method

Now Spring will take care of ignoring the fields mentioned in SimpleBeanPropertyFilter on serialization.

That's all folks!

- @IamVickyAV