Jersey / Jackson-类对象序列化

Question

I've found a lot of suggestions how to serialize Date correctly, but there is nothing that applicable for the next case:

public class CustomFilter {
    private String filterName;
    private List<Filter> filters;
    //getters and setters
}

public class Filter {
    private String propertyName;
    private String comparison;
    private Object value;
    //getters and setters
}

The issue is that value property in Filter can be a String, Number or Date. So instance of CustomFilter is serialized/desrialized properly (between Client and Resource), but if Filter value is Date it represents as long, if it is Joda-based Date the one represents as LinkedHashMap of elements (when deserialized). If anyone has idea how to handle this case (when object property is a type of Object but can be any of types described above) - please leave a comment

Answer 1

One option would be to create a container object which holds one of the three types

public class ValueHolder {
    private Date date;
    private JodatDate jodaDate;
    private Number number;
    private String string;
    // getters and setters omitted
    // maybe add additional logic to ensure only one value is set.
}

Then you should be able to deserialize/serialize it without any problems. If you want to do it with a custom serializer without the container object, you need to write the type of object in the json output and use that information to deserialize it on the receiving side.

Answer 2

If my understanding is correct, it doesn't matter if you deserialize keeping the "value" as an Object variable. How you handle the Object variable after deserializing is what you should be thinking about.

I tried the below with Jackson.

Create a class Address.

public class Address {
    private String street;
    private String city; 
    private Object zip;
    public String getStreet() {
        return street;
    }
    public void setStreet(String street) {
        this.street = street;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public Object getZip() {
        return zip;
    }
    public void setZip(Object zip) {
        this.zip = zip;
    }
}

Create a class Id.

 public class Id {
    private String fname;
    private String lname;
    private Address addr;
    public String getFname() {
        return fname;
    }
    public void setFname(String fname) {
        this.fname = fname;
    }
    public String getLname() {
        return lname;
    }
    public void setLname(String lname) {
        this.lname = lname;
    }
    public Address getAddr() {
        return addr;
    }
    public void setAddr(Address addr) {
        this.addr = addr;
    }
}

Main method:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {
    public static void main(String[] args) {
        long zip = 12345;

        Address addressObj = new Address();
        addressObj.setCity("Chicago");
        addressObj.setStreet("Some Street");
        addressObj.setZip(12345);

        Id idObj = new Id();
        idObj.setAddr(addressObj);
        idObj.setFname("Test");
        idObj.setLname("Tester");

        ObjectMapper mapper = new ObjectMapper();

        //Object to JSON in String
        try {
            String jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(idObj);
            System.out.println(jsonInString);
        } catch (JsonProcessingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       
    }
}

Output:

{
  "fname" : "Test",
  "lname" : "Tester",
  "addr" : {
    "street" : "Some Street",
    "city" : "Chicago",
    "zip" : 12345
  }
}

If in the main method, I change the zip to DateTime zip = new DateTime(DateTimeZone.UTC); result is as below:

{
  "fname" : "Test",
  "lname" : "Tester",
  "addr" : {
    "street" : "Some Street",
    "city" : "Chicago",
    "zip" : {
      "weekOfWeekyear" : 40,
      "dayOfWeek" : 1,
      "dayOfMonth" : 3,
      "dayOfYear" : 277,
      "weekyear" : 2016,
      "monthOfYear" : 10,
      "year" : 2016,
      "yearOfEra" : 2016,
      "yearOfCentury" : 16,
      "centuryOfEra" : 20,
      "era" : 1,
      "millisOfDay" : 83656626,
      "millisOfSecond" : 626,
      "secondOfMinute" : 16,
      "secondOfDay" : 83656,
      "minuteOfHour" : 14,
      "minuteOfDay" : 1394,
      "hourOfDay" : 23,
      "chronology" : {
        "zone" : {
          "fixed" : true,
          "id" : "UTC"
        }
      },
      "zone" : {
        "fixed" : true,
        "id" : "UTC"
      },
      "millis" : 1475536456626,
      "afterNow" : false,
      "beforeNow" : true,
      "equalNow" : false
    }
  }
}

The point here is that what you do with the Object variable is what matters