contract-to-serialize

/*
##################################################################################
##################################################################################
######### IF YOU FOUND THIS GIST USEFUL, PLEASE LEAVE A STAR. THANKS. ############
##################################################################################
##################################################################################
*/

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import java.util.Map;

public class CustomTypeUpdateContract {

  @JsonSerialize(keyUsing = MyCustomTypeMapKeySerializer.class)
  @JsonDeserialize(keyUsing = MyCustomTypeMapKeyDeserializer.class)
  private Map<MyCustomType, MyCustomType> oldValToNewValMap;

  public Map<MyCustomType, MyCustomType> getOldValToNewValMap() {
    return oldValToNewValMap;
  }

  public void setOldValToNewValMap(Map<MyCustomType, MyCustomType> oldValToNewValMap) {
    this.oldValToNewValMap = oldValToNewValMap;
  }
}

custom-type-deserializer

import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.KeyDeserializer;

import java.lang.reflect.Field;

public class MyCustomTypeMapKeyDeserializer extends KeyDeserializer {

  @Override
  public MyCustomType deserializeKey(String serializedString, DeserializationContext ctxt) {

    String[] fieldVals = serializedString.split(",");
    Field[] fields = MyCustomType.class.getDeclaredFields();
    MyCustomType myCustomType = new MyCustomType();
    for (int index = 0; index < fieldVals.length; index++) {
      String value = fieldVals[index];
      if (value.equals("null")) {
        continue;
      }
      try {
        fields[index].setAccessible(true);
        Class type = fields[index].getType();
        if (type == Integer.class) {
          fields[index].set(myCustomType, Integer.parseInt(value));
        } else {
          fields[index].set(myCustomType, value);
        }
      } catch (IllegalAccessException exception) {

      }
    }
    return myCustomType;
  }
}

custom-type-serializer

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

public class MyCustomTypeMapKeySerializer extends JsonSerializer<MyCustomType> {


  @Override
  public void serialize(MyCustomType myCustomType, JsonGenerator gen, SerializerProvider serializers) throws IOException {
    Field[] fields = MyCustomType.class.getDeclaredFields();

    List<String> fieldVals = new ArrayList<>();

    for (Field field : fields) {
      field.setAccessible(true);
      String fieldName = field.getName();
      try {
        if (!field.isSynthetic()) {
          // This synthetic check is required because in order to collect execution data, JaCoCo instruments the
          // classes under test which adds two members to the classes: A private static field $jacocoData and a private static method $jacocoInit().
          // Both members are marked as synthetic.

          fieldVals.add(String.valueOf(field.get(myCustomType)));
        }
      } catch (IllegalAccessException e) {
      }

    }
    gen.writeFieldName(String.join(",", fieldVals));
  }
}

Jackson Custom Serialization Sample3.md

Use Case:

• The object to be serialized/deserialized has a Map field whose key is another object that Jackson can't serialize or deserialize implicitly
• A third party library is responsible for serializing or deserializing the object eg. custom serialization of api response contracts in a spring webapplication. i.e the ObjectMapper cannot be accessed and configured directly

How am I doing it

• Using @JsonSerialize before Map field to register a custom serializer for the key.

mycustomtype

public class MyCustomType {
  private String id;
  private String name;
  private int val;

  public MyCustomType() {
  }

  public MyCustomType(String id, String name, int val) {
    this.id = id;
    this.name = name;
    this.val = val;
  }

  public String getId() {
    return id;
  }

  public void setId(String id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public int getVal() {
    return val;
  }

  public void setVal(int val) {
    this.val = val;
  }
}

testing

    Map<MyCustomType, MyCustomType> oldValToNewValMap = new HashMap<>();
    MyCustomType oldVal = new MyCustomType("ID#0001","type1",10);
    MyCustomType newVal = new MyCustomType("ID#0001", "type1",11);

    oldValToNewValMap.put(oldVal, newVal);
    CustomTypeUpdateContract customTypeUpdateContract = new CustomTypeUpdateContract();
    customTypeUpdateContract.setOldValToNewValMap(oldValToNewValMap);

    System.out.println(new ObjectMapper().writeValueAsString(customTypeUpdateContract));
    //outputs
    //{"oldValToNewValMap":{"ID#0001,type1,10":{"id":"ID#0001","name":"type1","val":11}}}