Avoid boilerplate code for POJOs representing JSONs

Question

I am creating a library of lots of different NetworkMessages that are normally in a JSON format, and now a corresponding Java model is needed.

The thing about it is that those messages can easily have about 100 fields in a JSON. Some of them are mandatory (30%), and some of them are optional (70%).

So the big concern that I have, is how to minimise the boiler plate code in the corresponding model. Because, like I said, those POJOs could easily have about 100 fields, and that many getters, and that many fields in a constructor.

I will give an example of one small Message, but keep in mind the messages are normally significantly bigger (more fields).

MessageA.java

@JsonInclude(Include.NON_EMPTY)
public class MessageA extends NetworkMessage {

    private final String a;

    private final String b;

    private final String c;

    private final String d;

    private final String e;

    private final String f;

    private final String g;

    private final String h;

    private final String i;

    private final String j;

    private final String k;

    @JsonCreator
    private MessageA(
            // required fields
            @JsonProperty(value = "a", required = true) String a, 
            @JsonProperty(value = "b", required = true) String b,
            @JsonProperty(value = "c", required = true) String c,
            @JsonProperty(value = "d", required = true) String d, 
            @JsonProperty(value = "e", required = true) String e, 
            @JsonProperty(value = "f", required = true) String f,

            // optional fields
            @JsonProperty(value = "g") String g, 
            @JsonProperty(value = "h") String h, 
            @JsonProperty(value = "i") String i, 
            @JsonProperty(value = "j") String j,
            @JsonProperty(value = "k") String k) {

        this.a = a;
        this.b = b;
        this.c = c;
        this.d = d;
        this.e = e;
        this.f = f;
        this.g = g;
        this.h = h;
        this.i = i;
        this.j = j;
        this.k = k;
    }

    public Optional<String> getG() {
        return Optional.ofNullable(g);
    }

    public Optional<String> getH() {
        return Optional.ofNullable(h);
    }

    public Optional<String> getI() {
        return Optional.ofNullable(i);
    }

    public Optional<MessageType> getJ() {
        return Optional.ofNullable(j);
    }

    public Optional<String> getK() {
        return Optional.ofNullable(k);
    }

    public String getA() {
        return a;
    }

    public String getB() {
        return b;
    }

    public String getC() {
        return c;
    }

    public String getD() {
        return d;
    }

    public String getE() {
        return e;
    }

    public String getF() {
        return f;
    }
}

Now, I tried to solve some of that by using Google's AutoValue library, and the code then looked a little better, but still there's the invocation of a constructor with many, many fields.

MessageA.java

@AutoValue
@JsonInclude(Include.NON_EMPTY)
public abstract class MessageA extends NetworkMessage {

    // required fields
    @Nonnull public abstract String getFieldA();

    @Nonnull public abstract String getFieldB();

    @Nonnull public abstract String getFieldC();

    @Nonnull public abstract String getFieldD();

    @Nonnull public abstract String getFieldE();

    @Nonnull public abstract String getFieldF();

    // optional fields
    @Nullable public abstract String getFieldG();

    @Nullable public abstract String getFieldH();

    @Nullable public abstract String getFieldI();

    @Nullable public abstract String getFieldJ();

    @Nullable public abstract String getFieldK();

    @JsonCreator
    private static MessageA create(
              // required fields
              @JsonProperty(value = "a", required = true) String a,
              @JsonProperty(value = "b", required = true) String b,
            @JsonProperty(value = "c", required = true) String c,
            @JsonProperty(value = "d", required = true) String d,
            @JsonProperty(value = "e", required = true) String e,
            @JsonProperty(value = "f", required = true) String f,

            // optional fields
            @JsonProperty(value = "g") String g,
            @JsonProperty(value = "h") String h,
            @JsonProperty(value = "i") String i,
            @JsonProperty(value = "j") String j,
            @JsonProperty(value = "k") String k) {

        return new AutoValue_MessageA(
                a, b, c, d, e, f, g, h, I, j, k);
    }
}

Now this is better, but there's a problem that I can't have Optional return types, so I could have null values floating through my code, and lots of null-checks should be performed in other places.

What would be your advice, which way to go with this?

Answer 1

If you really want/need to represent those Json messages as POJOs, you could at least get around all that boilerplate getter/setter/Ctor noise by only defining the needed Fields and use Lombok for getter/setter/Ctor generation. By annotating the class with @Data @Data you would get the getters/setter/ctor for free without ever seeing the Boilerplate involved.

@Data
public class MessageA extends NetworkMessage {

private final String a;

Would lead to a class that looks like this (and more)

@Data
public class MessageA extends NetworkMessage {

private final String a;
public MessageA(String a){
  this.a=a;
}
public String getA(){
  return this.a;
}

/*
*No setter since the field is private
*public void setA(String a){
*  this.a=a;
*}

*public boolean equals(Object o){...}
*public String toString(){...}
*/

I'm using lombok all the time to avoid soem of the necessary clutter.

But maybe you are better off avaiding those dataclasses at all. Such huge messages don't look like they are representing ONE concept but several nested concepts. Otherwise just store the JSON as JSONObject and provide getters that get the values from the JSON directly (you will have an easier time to configure/validate complex condition that way)