Agfdhyk

I am trying to read a json message from kafka and got an exception, which says Jackson cannot deserialize the json to POJO.

The json is like {"code":"500","count":22,"from":1528343820000,"to":1528343880000}, which is an output of kafka stream.

The POJO declares all attributes of the json, and is exactly the same POJO to produce the json message. So I have no idea why it would happen.

I am using spring cloud stream 2.0.0.RELEASE.

Any help would be appreciated. Thanks.

POJO:

public class CodeCount {

    private String code;

    private long count;

    private Date from;

    private Date to;



    @Override

    public String toString() {

        return "CodeCount [code=" + code + ", count=" + count + ", from=" + from + ", to=" + to + "]";

    }



    public CodeCount(String code, long count, Date from, Date to) {

        super();

        this.code = code;

        this.count = count;

        this.from = from;

        this.to = to;

    }



    public String getCode() {

        return code;

    }



    public void setCode(String code) {

        this.code = code;

    }



    public long getCount() {

        return count;

    }



    public void setCount(long count) {

        this.count = count;

    }



    public Date getFrom() {

        return from;

    }



    public void setFrom(Date from) {

        this.from = from;

    }



    public Date getTo() {

        return to;

    }



    public void setTo(Date to) {

        this.to = to;

    }

}

Stacktrace:

2018-06-07 15:18:51.572 ERROR 1 --- [container-0-C-1] o.s.integration.handler.LoggingHandler   : org.springframework.messaging.converter.MessageConversionException: Could not read JSON: Cannot construct instance of `com.example.CodeCount` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

 at [Source: (byte)"{"code":"500","count":22,"from":1528343820000,"to":1528343880000}"; line: 1, column: 2]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.example.CodeCount` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1275) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:325) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3109) ~[jackson-databind-2.9.3.jar!/:2.9.3]

at org.springframework.messaging.converter.MappingJackson2MessageConverter.convertFromInternal(MappingJackson2MessageConverter.java:221) ~[spring-messaging-5.0.6.RELEASE.jar!/:5.0.6.RELEASE]

... 37 common frames omitted

Jackson needs access to the default constructor to deserialize, add the default constructor to the pojo, ie:

public CodeCount() {

}

You can annotate the existing constructor, and args, and Jackson will use this:

@JsonCreator

public CodeCount(@JsonProperty("code") String code, 

                 @JsonProperty("count") long count, 

                 @JsonProperty("from") Date from, 

                 @JsonProperty("to") Date to) {

    super();

    this.code = code;

    this.count = count;

    this.from = from;

    this.to = to;

}

Passing in the dates may complicate it a bit, but it is definitely still possible.