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spring boot mvc – Content type ‘application/json;charset=UTF-8’ not supported

In this spring boot project I get an error when POSTing (using Postman) a new Item resource

Resolving exception from handler 
     [public com.example.demo.resource.Item com.example.demo.controller.ItemController.addItem(com.example.demo.resource.Item)]: 
     org.springframework.web.HttpMediaTypeNotSupportedException: 
     Content type 'application/json;charset=UTF-8' not supported

In the request body I copied one of the existing Items that I got from a GET request (and changed the id and itemName)

    // Request body:
    {
        "id": 10, // also tried without id field as it's autogenerated
        "itemName": "milk",
        "cart": {
            "id": 1
        }
    }

I made sure that I have the correct getters and setters in the Item class (as this is a known issue)

@Entity
@Table(name="items")
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@JsonIdentityInfo(
          generator = ObjectIdGenerators.PropertyGenerator.class, 
          property = "id")
public class Item
{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "item_id")
    private long id;

    @Column(name="item_name")
    private String itemName;

    @ManyToOne
    @JoinColumn(name = "cart_id", nullable=false)
    @JsonManagedReference
    private Cart cart;

   //setters and getters
}

Here is also the Cart class to which Item has a many-to-one relationship

@Entity
@Table(name="carts")
@JsonIdentityInfo(
          generator = ObjectIdGenerators.PropertyGenerator.class, 
          property = "id")
public class Cart 
{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "cart_id")
    private long id;

    @OneToMany(mappedBy = "cart")
    @JsonBackReference
    private Set<Item> items;

    //setters and getters
}

This is the ItemController

@RestController
public class ItemController 
{
    private static final Logger LOG = LoggerFactory.getLogger(ItemController.class);

    @Autowired ItemDao dao;

    @GetMapping("items")
    public List<Item> getAll()
    {
        List<Item> res = new ArrayList<>();
        dao.findAll().forEach(res::add);
        return res;
    }

    @PostMapping("items")
    public Item addItem(@RequestBody Item item)
    {
        return dao.save(item);
    }

    @GetMapping("items/{item_id}")
    public Item getItemById(@PathVariable("item_id") long item_id)
    {
        Item item = dao.findById(item_id).get();
        LOG.info(" ---------------- Retrieved item: {}", item.toString());
        return item;
    }
}

EDIT

I just noticed that there seems to be another error preceding:

Failed to evaluate Jackson deserialization for type [[simple type, class com.example.demo.resource.Item]]: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot handle managed/back reference 'defaultReference': back reference type (java.util.Set) not compatible with managed type (com.example.demo.resource.Item)

Here is the full error:

2018-02-27 11:03:09.836  WARN 9640 --- [nio-9200-exec-1] .c.j.MappingJackson2HttpMessageConverter : Failed to evaluate Jackson deserialization for type [[simple type, class com.example.demo.resource.Item]]: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot handle managed/back reference 'defaultReference': back reference type (java.util.Set) not compatible with managed type (com.example.demo.resource.Item)
2018-02-27 11:03:09.837  WARN 9640 --- [nio-9200-exec-1] .c.j.MappingJackson2HttpMessageConverter : Failed to evaluate Jackson deserialization for type [[simple type, class com.example.demo.resource.Item]]: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot handle managed/back reference 'defaultReference': back reference type (java.util.Set) not compatible with managed type (com.example.demo.resource.Item)
2018-02-27 11:03:09.838 DEBUG 9640 --- [nio-9200-exec-1] .w.s.m.m.a.ServletInvocableHandlerMethod : Failed to resolve argument 0 of type 'com.example.demo.resource.Item'

org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported

Thanks for the help

Answer

You can not use Collection, Map, Array or enumeration as @JsonBackReference .

Refer the link : https://fasterxml.github.io/jackson-annotations/javadoc/2.2.0/com/fasterxml/jackson/annotation/JsonBackReference.html.

Try interchanging @JsonBackReference and @JsonManagedReference. It should work.

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