Jackson ObjectMapper upper/lower case issues

Question

When I serialize/deserialize any object, all field names are converted to lower case. Is there any configuration to set that makes Jackson keep the field names exactly as they are? Both for serializing and deserializing?

(I know about @JsonProperty, but this does not seems to be right, since what I need is just for Jackson to respect what already exists)

My test code:

import java.io.Serializable;

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.cfg.MapperConfig;
import com.fasterxml.jackson.databind.introspect.AnnotatedField;
import com.fasterxml.jackson.databind.introspect.AnnotatedMethod;

public class Test {

    static class Example implements Serializable {
        private String Test;
        private String ABC;
        private String XyZ;

        public String getTest() { return Test; }
        public void setTest(String test) { Test = test; }

        public String getABC() { return ABC; }
        public void setABC(String abc) { ABC = abc; }

        public String getXyZ() { return XyZ; }
        public void setXyZ(String xyz) { XyZ = xyz; }
    }

    static class MyPropertyNamingStrategy extends PropertyNamingStrategy {
        @Override
        public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
            return convert(defaultName);
        }
        @Override
        public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
            return convert(defaultName);
        }
        @Override
        public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
            return convert(defaultName);
        }
        private String convert(String input) {
            return input;
        }
    }

    public static void main(String[] args) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper()
        .setPropertyNamingStrategy(new MyPropertyNamingStrategy())
        .enable(SerializationFeature.INDENT_OUTPUT)
        .configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);      

        //From OBJECT to JSON
        Example ex = new Example();
        ex.setTest("1");
        ex.setABC("2");
        ex.setXyZ("3");
        System.out.println(objectMapper.writeValueAsString(ex));

        //FROM JSON to OBJECT
        String jsonString = "{ \"Test\":\"0\", \"ABC\":\"1\", \"XyZ\":\"2\" }";
        Example fEx = objectMapper.readValue(jsonString, Example.class);
    }   

}

Thanks to @BlueLettuce16, I have managed to build an 'improved' version of the PropertyNamingStrategy. Here it is:

import java.lang.reflect.Modifier;

import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.cfg.MapperConfig;
import com.fasterxml.jackson.databind.introspect.AnnotatedField;
import com.fasterxml.jackson.databind.introspect.AnnotatedMethod;

public class CustomPropertyNamingStrategy extends PropertyNamingStrategy {

    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
        return convertForField(defaultName);
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convertForMethod(method, defaultName);
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convertForMethod(method, defaultName);
    }

    private String convertForField(String defaultName) {
        return defaultName;
    }

    private String convertForMethod(AnnotatedMethod method, String defaultName) {
        if (isGetter(method)) {
            return method.getName().substring(3);
        }
        if (isSetter(method)) {
            return method.getName().substring(3);
        }
        return defaultName;
    }

    private boolean isGetter(AnnotatedMethod method) {
        if (Modifier.isPublic(method.getModifiers()) && method.getGenericParameterTypes().length == 0) {
            if (method.getName().matches("^get[A-Z].*") && !method.getGenericReturnType().equals(void.class))
                return true;
            if (method.getName().matches("^is[A-Z].*") && method.getGenericReturnType().equals(boolean.class))
                return true;
        }
        return false;
    }

    private boolean isSetter(AnnotatedMethod method) {
        return Modifier.isPublic(method.getModifiers()) && method.getGenericReturnType().equals(void.class) && method.getGenericParameterTypes().length == 1
                && method.getName().matches("^set[A-Z].*");
    }

}

Answer 1

Even though @JsonProperty doesn't work, I was able to use @JsonSetter and @JsonGetter to map capitalized json field names.

@JsonSetter("ABC")
public void setABC(String ABC) {
    this.ABC= ABC;
}

Spring will now serialize the object field as "ABC" and not "abc".

Answer 2

I've had the same problem.

This is my solution:

public class MyNamingStrategy extends PropertyNamingStrategy {

    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
        return field.getName();
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convert(method, defaultName);
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convert(method, defaultName);
    }

    private String convert(AnnotatedMethod method, String defaultName) {

        Class<?> clazz = method.getDeclaringClass();
        List<Field> flds = FieldUtils.getAllFieldsList(clazz);
        for (Field fld : flds) {
            if (fld.getName().equalsIgnoreCase(defaultName)) {
                return fld.getName();
            }
        }

        return defaultName;
    }
}

In this case you will get the exact name of the property, and will not have to depend on the correct names of the methods.

Answer 3

I think that this is the solution (using custom PropertyNamingStrategy):

import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.databind.cfg.MapperConfig;
import com.fasterxml.jackson.databind.introspect.AnnotatedField;
import com.fasterxml.jackson.databind.introspect.AnnotatedMethod;

public class MyPropertyNamingStrategy extends PropertyNamingStrategy {
    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
        return convert(field.getName());
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convert(method.getName().toString());
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return convert(method.getName().toString());
    }

    private String convert(String input) {
        return input.substring(3);
    }
}

Test

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.IOException;
import java.io.StringWriter;

public class MyPropertyNamingStrategyTest {
    public static void main(String[] args) {
        PrivatePerson privatePerson = new PrivatePerson();
        privatePerson.setFirstName("John");
        privatePerson.setLastName("Smith");

        ObjectMapper mapper = new ObjectMapper();
        mapper.setPropertyNamingStrategy(new MyPropertyNamingStrategy());
        mapper.enable(SerializationFeature.INDENT_OUTPUT);
        StringWriter sw = new StringWriter();
        try {
            mapper.writeValue(sw, privatePerson);
        } catch (IOException e) {
            e.printStackTrace();
        }
        System.out.println(sw.toString());
    }
}

PrivatePerson

public class PrivatePerson {
    private String firstName;
    private String lastName;

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getLastName() {
        return lastName;
    }
}

Answer 4

You can configure Jackson to be case sensitivity tolerant:

ObjectMapper mapper = new ObjectMapper();
mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);

Cudos to https://stackoverflow.com/a/32842962/1639556

Answer 5

Using @JsonProperty annotation. It work well

Example

@JsonProperty("Code")
private String Code;
@JsonProperty("Message")
private String Message;