com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException：无法识别的字段

Question

i got a deserialization problem:

This is my class:

public class Response {

    private Object ResObj;
    private int ResInt;

    public Object getResObj() {
        return ResObj;
    }

    public int getResInt() {
        return ResInt;
    } 
} 

the JSON i want to deserialize is:

{"ResObj":{"ClientNum":"12345","ServerNum":"78945","IdNum":"020252"},"ResInt":0}

I get this exception:

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "ResObj" , not marked as ignorable (0 known properties: ])
 at [Source: java.io.StringReader@1f758500; line: 1, column: 20] (through reference chain: ["ResObj"])

I don't want to add:

@JsonIgnoreProperties(ignoreUnknown = true)

because I want to get the ResObj...

if I add the annotation, it pass but it will set it as null .. which I don't want.

Answer 1

If you don't want to have a setter in your bean and only use fields and getters, you can use the visibility checker of ObjectMapper to allow field visibility.
Something like following:

ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
mapper.setVisibility(VisibilityChecker.Std.defaultInstance().withFieldVisibility(JsonAutoDetect.Visibility.ANY));

Answer 2

You need Setter methods to allow Jackson to set the properties, and you need to change the fields in the json to begin with a lower case letter:

public class Response {

    private Object ResObj;
    private int ResInt;

    public Object getResObj() {
        return ResObj;
    }

    public void setResObj(Object ResObj) {
        this.ResObj = ResObj;
    }

    // ...
}

and:

{"resObj":{"clientNum":"12345","serverNum":"78945","idNum":"020252"},"resInt":0}

The reason for the JSON change is that the Jackson bean serialisation will reflect over the class, and when it sees getXyz() and setXyz() methods will map these to a Json filed names "xyz" (and not "Xyz").

I think there are several ways to override this behaviour, one is to use the one of the Jackson annotations.

Answer 3

I think you should try this

public class Response {
    @JsonProperty
    private Object ResObj;
    @JsonProperty
    private int ResInt;

    public Object getResObj() {
        return ResObj;
    }

    public int getResInt() {
        return ResInt;
    } 
} 

It will resolve your issue with UnrecognizedPropertyExceptions

Answer 4

public class Response {
    public Object ResObj;
    public int ResInt;

    public Object getResObj() {
        return ResObj;
    }

    public int getResInt() {
        return ResInt;
    } 
} 

Use this to resolve the above issue.

Answer 5

I have sorted this problem using the Jackson library. Here is my code snippet.

**Main Class with JSON String in all lower case:**

 public class MainClass {

public static void main(String[] args) throws JsonParseException, 
    JsonMappingException, IOException {

    String jsonStr = "{\r\n" + "    \"resObj\": {\r\n" + "      \"clientNum\": 
               \"12345\",\r\n"
            + "     \"serverNum\": \"78945\",\r\n" + "      \"idNum\": 
          \"020252\"\r\n" + "   },\r\n"
            + " \"resInt\": 0\r\n" + "}";

    ObjectMapper mapper = new ObjectMapper();

    MyPojo details = mapper.readValue(jsonStr, MyPojo.class);

    System.out.println("value of clientNum: " + details.getResObj().getClientNum());
    System.out.println("value of getServerNum: " + 
               details.getResObj().getServerNum());
    System.out.println("value of getIdNum: " + details.getResObj().getIdNum());
    System.out.println("value of getResInt: " + details.getResInt());

} }

**MyPojo Class:**

 public class MyPojo {
private ResObj resObj;

private String resInt;

public ResObj getResObj() {
    return resObj;
}

  public String getResInt() {
       return resInt;   } }

**ResObj class:**


public class ResObj {
private String serverNum;

private String idNum;

private String clientNum;

public String getServerNum() {
    return serverNum;
}

public String getIdNum() {
    return idNum;
}

public String getClientNum() {
    return clientNum;
} }

**RESULT**

  value of clientNum: 12345
  value of getServerNum: 78945
  value of getIdNum: 020252
  value of getResInt: 0

NOTE: I have removed Setters in classes & there is no effect on the result.

Answer 6

I tried all the ways mentioned above but in my case, this is the only solution that worked as answered here Solution 2. Here I have enabled @EnableWebMvc in my spring boot application.

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
    @Autowired
    private ObjectMapper objectMapper;// created elsewhere
    @Override
    public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
        // this will add a 2nd MappingJackson2HttpMessageConverter 
        converters.add(new MappingJackson2HttpMessageConverter(this.objectMapper));
    }
}

Answer 7

You need to define another class for the information within ResObj {"ClientNum":"12345","ServerNum":"78945","IdNum":"020252"}. Otherwise jackson cannot determine how to deserialize.