Firebase util class to serialize and deserialize Object for Firebase 9.2.0 using Auto-Value and Jackson.

FirebaseUtil.java

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.GenericTypeIndicator;

import java.util.Map;

public enum FirebaseUtil {
    ;

    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
    private static final JavaType JAVA_TYPE = OBJECT_MAPPER.getTypeFactory().constructMapType(Map.class, String.class, Object.class);

    static {
        OBJECT_MAPPER.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
    }

    public static Map<String, Object> serialize(Object o) {
        // Convert to a Map<String,Object> using Jackson and then pass that to Firebase
        return OBJECT_MAPPER.convertValue(o, JAVA_TYPE);
    }

    public static <T> T deserialize(DataSnapshot dataSnapshot, Class<T> tClass) {
        // Use Firebase to convert to a Map<String,Object>
        GenericTypeIndicator<Map<String, Object>> genericTypeIndicator = new GenericTypeIndicator<Map<String, Object>>() {
        };
        Map<String, Object> map = dataSnapshot.getValue(genericTypeIndicator);
        // Use Jackson to convert from a Map to an Office object
        return OBJECT_MAPPER.convertValue(map, tClass);
    }

}

Phone.java

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.auto.value.AutoValue;

@AutoValue
@JsonDeserialize(builder = AutoValue_Phone.Builder.class)
public abstract class Phone {

    @JsonProperty("type")
    public abstract int type();

    @JsonProperty("number")
    public abstract String number();
    
    @AutoValue.Builder
    public static abstract class Builder {
        
        @JsonProperty("type")
    public abstract Builder type(int type);

    @JsonProperty("number")
    public abstract Builder number(String number);
    
    public abstract Phone build();
        
    }

}

User.java

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.auto.value.AutoValue;

import java.util.List;

@AutoValue
@JsonDeserialize(builder = AutoValue_User.Builder.class)
public abstract class User {

    @JsonProperty("first_name")
    public abstract String firstName();

    @JsonProperty("last_name")
    public abstract String lastName();

    @JsonProperty("phones")
    public abstract List<Phone> phones();
    
    @AutoValue.Builder
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static abstract class Builder {
        
        @JsonProperty("first_name")
        public abstract Builder firstName(String firstName);
    
        @JsonProperty("last_name")
        public abstract Builder lastName(String lastName);
    
        @JsonProperty("phones")
        public abstract Builder phones(List<Phone> phones);
        
        public abstract User build();
        
    }

}