Using an objectmapper instance to deserialize a json list to a VO works fine, This VO uses @JsonValue, but uses springboot’s objectmapper, which results in an error.

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type Rankings from Array value (token JsonToken.START_ARRAY)
at [Source: (String)”[{“time”: 1718198341000, “account”: “Coder-001”, “maxScore”: “0.4247”, “submitCount”: 1}]”; line: 1, column: 1]

Here is my code, using lombok.

@Value
@AllArgsConstructor(onConstructor = @__(@JsonCreator))
public class Rankings {

    @JsonValue
    List<Ranking> rankings;

    public List<Ranking> getRankings() {
        return MoreObjects.firstNonNull(rankings, ImmutableList.of());
    }
}


@Builder
@JsonIgnoreProperties(ignoreUnknown = true)
@AllArgsConstructor(onConstructor = @__(@JsonCreator))
@Value
public class Ranking implements Comparable<Ranking> {

    @JsonProperty("account")
    String account;
    @JsonProperty("maxScore")
    String maxScore;
    @JsonProperty("submitCount")
    Integer submitCount;
    @JsonProperty("time")
    Long time;

    @Override
    public int compareTo(Ranking o) {
        int i = new BigDecimal(maxScore).compareTo(new BigDecimal(o.maxScore));
        if (i != 0) {
            return i;
        }
        return submitCount.compareTo(o.submitCount);
    }
}

using a new ObjectMapper instance, everything works fine, and a error was throwed when using spring boot objectmapper bean.

// works fine
Rankings rankings = new ObjectMapper().readValue("[{"time": 1718198341000, "account": "Coder-001", "maxScore": "0.4247", "submitCount": 1}]", Rankings.class);


// com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `Rankings` from Array value (token `JsonToken.START_ARRAY`)

Rankings rankings = SpringContextHolder.getBean(ObjectMapper.class).readValue("[{"time": 1718198341000, "account": "Coder-001", "maxScore": "0.4247", "submitCount": 1}]", Rankings.class);

Now I’m confused, i wan’t to know the reason.

help