[FIXED] Using Jackson to extract information from Property names

Issue

I currently receive the following JSON body

{
    "productId": "90000011",
    "offerId": "String",
    "format": "String",
    "sellerId": "String",
    "sellerName": "String",
    "shippingPrice[zone=BE,method=STD]": 0.0,
    "deliveryTimeEarliestDays[zone=BE,method=STD]": 1,
    "deliveryTimeLatestDays[zone=BE,method=STD]": 1,
    "shippingPrice[zone=NL,method=STD]": 0.0,
    "deliveryTimeEarliestDays[zone=NL,method=STD]": 1,
    "deliveryTimeLatestDays[zone=NL,method=STD]": 1
}

As you can see, I have similar properties that differ by zone and method enclosed in square brackets. I don't want to change the code every time a new zone and/or method is introduced. I'm looking for a more dynamic way you deserialize this via Jackson.

Is there a way to automatically deserialize all properties starting with shippingPrice, deliveryTimeEarliestDays and deliveryTimeLatestDays into the following format?

{
    "productId": "90000011",
    "offerId": "String",
    "format": "String",
    "sellerId": "String",
    "sellerName": "String",
    "deliveryModes":[
    {
        "method":"STD"
        "zone":"BE",
        "shippingPrice":0.0,
        "deliveryTimeEarliestDays":1,
        "deliveryTimeLatestDays":1
    },{
        "method":"STD"
        "zone":"NL",
        "shippingPrice":0.0,
        "deliveryTimeEarliestDays":1,
        "deliveryTimeLatestDays":1
    }]
}

My first idea was to use the @JsonAnySetter annotation and put everything in a Map but that still leaves me with manual parsing of the field name.

My Second Idea was to build a custom deserializer where I loop over all attributes and filter out all the ones that start with shippingPrice, deliveryTimeEarliestDays and deliveryTimeLatestDays and map them to the described format above.

Solution

In order to achieve the required result, you need to implement deserialization logic yourself, it can't be done only by sprinkling a couple of data binding annotations.

That's how it can be done.

Assume here's a POJO that corresponds to your input JSON (to avoid boilerplate code, I'll use Lombok annotations):

@Getter
@Setter
public static class MyPojo {
    private String productId;
    private String offerId;
    private String format;
    private String sellerId;
    private String sellerName;
    @JsonIgnore // we don't want to expose this field to Jackson as is
    private Map<DeliveryZoneMethod, DeliveryMode> deliveryModes = new HashMap<>();
    
    @JsonAnySetter
    public void setDeliveryModes(String property, String value) {
        DeliveryZoneMethod zoneMethod = DeliveryZoneMethod.parse(property);
        DeliveryMode mode = deliveryModes.computeIfAbsent(zoneMethod, DeliveryMode::new);
        
        String name = property.substring(0, property.indexOf('['));

        switch (name) {
            case "shippingPrice" -> mode.setShippingPrice(new BigDecimal(value));
            case "deliveryTimeEarliestDays" -> mode.setDeliveryTimeEarliestDays(Integer.parseInt(value));
            case "deliveryTimeLatestDays" -> mode.setDeliveryTimeLatestDays(Integer.parseInt(value));
        }
    }
    
    public Collection<DeliveryMode> getModes() {
        return deliveryModes.values();
    }
}

Properties productId, offerId, format, sellerId, sellerName would be parsed by Jackson in a regular way.

And all other properties formatted like "shippingPrice[zone=BE,method=STD]" would be handled by the method annotated with @JsonAnySetter.

To facilitate extracting and storing information from such properties I've defined a couple of auxiliary classes:

• DeliveryZoneMethod which contains information about a zone and delivery method as its name suggests (the purpose of this class is to serve as Key in the map deliveryModes).
• DeliveryMode which is meant to contain all the need information that correspond to a particular zone and method of delivery.

For conciseness, DeliveryZoneMethod can be implemented as a Java 16 record:

public record DeliveryZoneMethod(String method, String zone) {
    public static Pattern ZONE_METHOD = Pattern.compile(".+zone=(\\p{Alpha}+).*method=(\\p{Alpha}+)");
    public static DeliveryZoneMethod parse(String str) {
        // "shippingPrice[zone=BE,method=STD]" - assuming the given string has always the same format
        Matcher m = ZONE_METHOD.matcher(str);
        
        if (!m.find()) throw new IllegalArgumentException("Unable to parse: " + str);
        
        return new DeliveryZoneMethod(m.group(1), m.group(2));
    }
}

And here's how DeliveryMode might look like:

@Getter
@Setter
public static class DeliveryMode {
    private String method;
    private String zone;
    private BigDecimal shippingPrice;
    private int deliveryTimeEarliestDays;
    private int deliveryTimeLatestDays;
    
    public DeliveryMode(DeliveryZoneMethod zoneMethod) {
        this.method = zoneMethod.method();
        this.zone = zoneMethod.zone();
    }
}

Usage example:

public static void main(String[] args) throws JsonProcessingException {
    String json = """
        {
            "productId": "90000011",
            "offerId": "String",
            "format": "String",
            "sellerId": "String",
            "sellerName": "String",
            "shippingPrice[zone=BE,method=STD]": 0.0,
            "deliveryTimeEarliestDays[zone=BE,method=STD]": 1,
            "deliveryTimeLatestDays[zone=BE,method=STD]": 1,
            "shippingPrice[zone=NL,method=STD]": 0.0,
            "deliveryTimeEarliestDays[zone=NL,method=STD]": 1,
            "deliveryTimeLatestDays[zone=NL,method=STD]": 1
        }
        """;
    
    ObjectMapper mapper = new ObjectMapper();
    MyPojo myPojo = mapper.readValue(json,  MyPojo.class);

    String serializedJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(myPojo);
    
    System.out.println(serializedJson);
}

Output:

{
  "productId" : "90000011",
  "offerId" : "String",
  "format" : "String",
  "sellerId" : "String",
  "sellerName" : "String",
  "modes" : [ {
    "method" : "BE",
    "zone" : "STD",
    "shippingPrice" : 0.0,
    "deliveryTimeEarliestDays" : 1,
    "deliveryTimeLatestDays" : 1
  }, {
    "method" : "NL",
    "zone" : "STD",
    "shippingPrice" : 0.0,
    "deliveryTimeEarliestDays" : 1,
    "deliveryTimeLatestDays" : 1
  } ]
}

Answered By - Alexander Ivanchenko
Answer Checked By - David Marino (JavaFixing Volunteer)