Deserialize MongoDB date fields to Java POJO Using Jackson

Question

Using Spring Boot 1.4.4.RELEASE, have saved a RequestBody to MongoDB as below:

{
    "startTime" : NumberLong("1483542955570"),
    "startDate" : ISODate("2017-01-04T15:15:55.570Z"),
    "endTime" : NumberLong("1483542955570"),
    "endDate" : ISODate("2017-01-04T15:15:55.570Z")
}

While mapping this back to a Java POJO, I am trying the below code.

public <T> T getPOJOFromMongoDocument(Document resourceDocument, Class<T> clazz) {
        String serialize = JSON.serialize(resourceDocument);
        return objectMapper.readValue(serialize,
                                      clazz);
}

serialize has the date fields returned as following

"startDate" : { "$date" : "2017-01-04T15:15:55.570Z"}

Due to $date, Jackson ObjectMapper returns the below exception during parsing:

java.lang.RuntimeException: Error parsing mongoDoc to Pojo : errorMessage : {Can not deserialize instance of java.util.Date out of START_OBJECT token at [Source: {
"startTime": 1483542955570,
"startDate": {
    "$date": "2017-01-04T15:15:55.570Z"
},
"endTime": 1483542955570,
"endDate": {
    "$date": "2017-01-04T15:15:55.570Z"
}}; line: 1, column: 381] (through reference chain: com.gofynd.engine.mongo.models.RuleWithDataVO["validity"]->com.gofynd.engine.mongo.models.ValidityVO["startDate"])}

Is there way to solve this without using an ODM?

Answer 1

When deserializing to Date Jackson expects a String like "2017-01-04T15:15:55.570Z". Instead, it sees the start of another object (the { char) inside the JSON hence the exception.

Consider specifying your Pojo class and another MongoDate class similar to this:

class MongoDate {
    @JsonProperty("$date")
    Date date;
}

class Pojo {
    long startTime;
    long endTime;
    MongoDate startDate;
    MongoDate endDate;
}

Alternatively if you can't / don't want to add a MongoDate class you can introduce a custom deserializer for Date fields. In that case Pojo:

class Pojo {
    long startTime;
    long endTime;
    @JsonDeserialize(using = MongoDateConverter.class)
    Date startDate;
    @JsonDeserialize(using = MongoDateConverter.class)
    Date endDate;
}

And the deserializer would look like this:

class MongoDateConverter extends JsonDeserializer<Date> {
    private static final SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");

    @Override
    public Date deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
        JsonNode node = jp.readValueAsTree();
        try {
            return formatter.parse(node.get("$date").asText());
        } catch (ParseException e) {
            return null;
        }
    }
}