Java – get different JSON representations of the same object

Give a Java object serialized as a JSON string with Jackson

Compression:

{
  "a":"123","s":"100"
}

Or normal:

{
  "altitude":"123","speed":"100"
}

Edit: the goal I want to achieve through this goal is to have a long JSON format, which is suitable for debugging (human readable) and has a compressed format that provides minimum space

Solution

You can do this in many ways It depends on your requirements I suggest you implement your own attribute naming strategy See the following example:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategyBase {

    private static final long serialVersionUID = 1L;

    @Override
    public String translate(String name) {
        return String.valueOf(name.charAt(0));
    }
}

You can use it this way:

ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(new CompressedPropertyNamingStrategy());
String json = mapper.writeValueAsString(new Pojo());

If you don't want to compress attribute names, just delete line 2

Editor 1 after the @ aumand comment, I want to inform you that this solution does not apply to entities that contain many attributes starting with the same letter We have to write more complex solutions For example:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategyBase {

    private static final long serialVersionUID = 1L;

    private final int length;

    public CompressedPropertyNamingStrategy(int length) {
        this.length = length;
    }

    @Override
    public String translate(String name) {
        if (name.length() < length) {
            return name;
        }

        return name.substring(0,length);
    }
}

Edit 2 if you really want to control property names during serialization, you should implement your own comments For example:

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(value = { ElementType.METHOD,ElementType.FIELD })
@Retention(value = RetentionPolicy.RUNTIME)
public @interface CompressedName {
    String value();
}

In this case, your naming policy might be as follows:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategy {

    private static final long serialVersionUID = 1L;

    @Override
    public String nameForGetterMethod(MapperConfig<?> config,AnnotatedMethod method,String defaultName) {
        CompressedName compressedProperty = method.getAnnotation(CompressedName.class);
        if (compressedProperty != null) {
            return compressedProperty.value();
        }

        // Implement default value: first letter,or something else
        return defaultName;
    }
}

Now you must add comments to the entity method:

class Entity {

    private long altitude = 123;
    private int speed = 100;

    @CompressedName("a")
    public long getAltitude() {
        return altitude;
    }

    public void setAltitude(long altitude) {
        this.altitude = altitude;
    }

    @CompressedName("sp")
    public int getSpeed() {
        return speed;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }
}

In this scenario example, JSON may be as follows:

{"a":123,"sp":100}