Jackson：MismatchedInputException: Cannot construct instance of

2020年2月7日

データの仕様を変更したために、正しくデシリアライズできない事例が発生した。

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `foo.bar.MismatchedTest$Sample` (although at least one Creator exists): no int/Int-argument constructor/factory method to deserialize from Number value (123)
 at [Source: (String)"123"; line: 1, column: 1]
    at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
    at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1343)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1032)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator.createFromInt(ValueInstantiator.java:262)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromInt(StdValueInstantiator.java:356)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromNumber(BeanDeserializerBase.java:1324)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:173)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:161)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4014)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3005)

このエラーは以下のようなコードで確認できる。

import org.junit.*;

import com.fasterxml.jackson.annotation.*;
import com.fasterxml.jackson.annotation.JsonAutoDetect.*;
import com.fasterxml.jackson.annotation.JsonInclude.*;
import com.fasterxml.jackson.databind.*;

public class MismatchedTest {

  static ObjectMapper mapper = new ObjectMapper()
      .setVisibility(PropertyAccessor.ALL, Visibility.NONE)
      .setVisibility(PropertyAccessor.FIELD, Visibility.ANY)
      .setSerializationInclusion(Include.NON_NULL)
      .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
      .disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
      ;

  @Test
  public void test() throws Exception {
    String json = mapper.writeValueAsString(123);
    System.out.println(json);
    mapper.readValue(json, Sample.class);
  }

  public static class Sample {
    int id;
  }
}