Some Moshi adapters for solving common issues with JSON serialization: Null replace by specific value, exclude empty fields from json;

MoshiAdapters.java

package com.artfulbits.json.moshi;

import android.support.annotation.*;

import com.ryanharter.auto.value.moshi.MoshiAdapterFactory;
import com.squareup.moshi.FromJson;
import com.squareup.moshi.JsonAdapter;
import com.squareup.moshi.JsonQualifier;
import com.squareup.moshi.JsonReader;
import com.squareup.moshi.JsonWriter;
import com.squareup.moshi.ToJson;

import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@MoshiAdapterFactory
public abstract class MoshiFactory implements JsonAdapter.Factory {
    /** Static factory method to access the package, private generated implementation */
    @NonNull
    public static JsonAdapter.Factory create() {
        return new AutoValueMoshi_MoshiFactory();
    }

    @Retention(RetentionPolicy.RUNTIME)
    @JsonQualifier
    public @interface NullableLong {
        long NONE = -1;
    }

    @Retention(RetentionPolicy.RUNTIME)
    @JsonQualifier
    public @interface NullableDouble {
        double NONE = -1;
    }

    @Retention(RetentionPolicy.RUNTIME)
    @JsonQualifier
    public @interface ExcludeIfEmpty {
    }

    /** @see <a href="https://github.com/square/moshi/issues/114">Null for primitive types</a> */
    @SuppressWarnings("unused")
    public static class NullableAdapter {
        @ToJson
        public String toJsonLong(@NullableLong long value) {
            return (NullableLong.NONE == value ? null : String.valueOf(value));
        }

        @FromJson
        @NullableLong
        public long fromJsonLong(@NonNull final JsonReader reader) throws IOException {
            if (reader.peek() == JsonReader.Token.NUMBER) {
                return reader.nextLong();
            } else if (reader.peek() == JsonReader.Token.NULL) {
                reader.nextNull();
            }

            return NullableLong.NONE;
        }

        @ToJson
        public String toJsonDouble(@NullableDouble double value) {
            return (NullableDouble.NONE == value ? null : String.valueOf(value));
        }

        @FromJson
        @NullableDouble
        public double fromJsonDouble(@NonNull final JsonReader reader) throws IOException {
            if (reader.peek() == JsonReader.Token.NUMBER) {
                return reader.nextDouble();
            } else if (reader.peek() == JsonReader.Token.NULL) {
                reader.nextNull();
            }

            return NullableDouble.NONE;
        }

        @ToJson
        public void toJsonEmptyDouble(final JsonWriter writer, @ExcludeIfEmpty final double value) throws IOException {
            if (value != 0.0) {
                writer.value(String.valueOf(value));
            } else {
                writer.nullValue();
            }
        }

        @FromJson
        @ExcludeIfEmpty
        public double fromJsonEmptyDouble(@NonNull final JsonReader reader) throws IOException {
            return reader.nextDouble();
        }

        @ToJson
        public void toJsonEmptyLong(final JsonWriter writer, @ExcludeIfEmpty final long value) throws IOException {
            if (value != 0) {
                writer.value(String.valueOf(value));
            } else {
                writer.nullValue();
            }
        }

        @FromJson
        @ExcludeIfEmpty
        public long fromJsonEmptyLong(@NonNull final JsonReader reader) throws IOException {
            return reader.nextLong();
        }
    }
}

Usage:

Configure Moshi instance:

    private final Moshi moshi = new Moshi.Builder()
            .add(MoshiFactory.create())
            .add(new MoshiFactory.NullableAdapter())
            .build();

Use in POJO:

public class POJO {
    /** Optional. Should not be used right now by app. */
    @Json(name = "startDate") @MoshiFactory.ExcludeIfEmpty public long startDate;
    /** Instead of NULL set -1.0d; */
    @Json(name = "topUpAmount") @MoshiFactory.NullableDouble public double amount;
    /** Instead of NULL set -1L; */
    @Json(name = "triggerValue") @MoshiFactory.NullableLong public long trigger;
}

where we are using "AutoValueMoshi_MoshiFactory"

 private final Moshi moshi = new Moshi.Builder()
            .add(MoshiFactory.create())
            .add(new MoshiFactory.NullableAdapter())
            .build();

when we create instance of Moshi we register our Factory