Posted on

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 {
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    private Integer id;

          

          

           

            

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    private String name;

          

          

           

            

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    private Date dateOfBirth;

          

          

           

            

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    private String city;

          

          

           

            

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    // constructors, getters & setters are ignored

          

          

           

            

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}

          

          

           

            

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@RestController

          

          

           

            

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public class UserController {

          

          

           

            

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    @Autowired

          

          

           

            

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    UserService userService;

          

          

           

            

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

          

          

           

            

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

          

          

           

            

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        return userService.getUser(id);

          

          

           

            

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    }

          

          

           

            

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

          

          

           

            

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    List<User> getAllUsers(){

          

          

           

            

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        return userService.getAllUsers();

          

          

           

            

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    }

          

          

           

            

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}

          

         

        

       

      

     

     

      

     

     

      

       

      

     

    

   

  

 





	


	





		

		
Posted on 
Serializable Java Lambdas
	


			

			
							
		

	
	

		
Recently I was presented with the following error when serializing a lambda with Kryo:



 

  

   

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com.esotericsoftware.kryo.KryoException: 

          

          

           

            

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  java.lang.IllegalArgumentException: 

          

          

           

            

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    Unable to serialize Java Lambda expression, unless explicitly declared e.g., 

          

          

           

            

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    Runnable r = (Runnable & Serializable) () -> System.out.println("Hello world!");

          

         

        

       

      

     

     

      

     

     

      

       

      

     

    

   

  

 




If you do not recognize the (Runnable & Serializable) syntax, don’t worry, it is merely stating that the lambda must implement two types. This is called Type Intersection. Personally, I have never needed to use this myself, so have never really thought about it. Serializable is a bit of a unique interface in this regards, as there is nothing you actually need to implement.