Jackson ObjectMapper cannot deserialize POJO, throws an exception: No suitable constructor found for type [...]: can not instantiate from JSON object

Question

I have tried to test the following code with no success:

class TestClass
{
  private class ND2Customer
  {
    public String name;
    public String description;
    public String email;
    public Boolean multiuser;

    public String dnszone;
    public String uri;
    public String type;

    public ND2Customer()
    {

    }
  }

  @Test
  public void TestJackson() throws JsonParseException, JsonMappingException, IOException
  {
    String json="{\"description\": \"test1u\", \"dnszone\": \"test1.public.sevenltest.example.com.\", \"uri\": \"http://199.127.129.69/customer/test1\", \"multiuser\": true, \"type\": \"2.0.3-3146\", \"email\": \"test1@com.com\", \"name\": \"test1\"}";
    ObjectMapper mapper = new ObjectMapper();

    ND2Customer casted=mapper.readValue(json, ND2Customer.class);

    String castedback=mapper.defaultPrettyPrintingWriter().writeValueAsString(casted);
    System.out.println(castedback);
  } 
}

This problem is different from this one: Deserializing JSON with Jackson - Why JsonMappingException "No suitable constructor"?

and this one: JsonMappingException: No suitable constructor found for type [simple type, class ]: can not instantiate from JSON object

as I have manually override the default constructor, and its not a subclass.

How do I fix this problem?

score 58 · Accepted Answer · answered Oct 16 '12 at 16:47

58

Make it static. Jackson can not deserialize to inner classes

answered Oct 16 '12 at 16:47

eugen

5,856
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29
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2

Thanks, it works. Your solution perfectly makes sense, as Jackson mapper cannot initialize an inner class and return it. – tribbloid Oct 16 '12 at 19:34
3

Minor addition: Jackson can actually deserialize one kind of non-static inner classes -- those referenced directly by the parent class. But this is not the case here, as Test class is not being serialized. In this case non-staticness was probably accidental. – StaxMan Oct 17 '12 at 17:21
2

I would bet most of the "No suitable constructor" issues with nested POJOs are because of forgetting to mark it static. Thanks eugen! – Kirk B. Mar 20 '13 at 23:29

score 1 · Answer 2 · answered Oct 16 '12 at 14:23

1

The problem is probably that Jackson can't properly reach your ND2Customer class to invoke its constructor because it is private, as your class otherwise looks just fine. Try making it public and seeing if that works.

answered Oct 16 '12 at 14:23

Donal Fellows

133,037
18
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Sorry, I forgot to mention that ND2Customer is a nested class defined right before the @Test public void TestJackson(). – tribbloid Oct 16 '12 at 14:37
And changing it to public doesn't make anything different :) – tribbloid Oct 16 '12 at 14:39
3

“It is an inner class” was highly relevant… – Donal Fellows Oct 17 '12 at 13:38

Jackson ObjectMapper cannot deserialize POJO, throws an exception: No suitable constructor found for type [...]: can not instantiate from JSON object

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