Set value ​in static inner class and write object to JSON

Question

What is a better way to set the value of the variable c in class Nested and then write the nested object to JSON instead of how it was done in the main method?

    import lombok.Data;
    
    @Data
    public class Nested {
        private A a;
    
        @Data
        public static class A {
            private B b;
    
            @Data
            public static class B {
                private int c;
            }
        }
    }

import javax.json.bind.JsonbBuilder;

public class Main {
    public static void main(String[] args) {
        Nested nested = new Nested();
        Nested.A a = new Nested.A();
        Nested.A.B b = new Nested.A.B();
        b.setC(123);

        a.setB(b);
        nested.setA(a);

        System.out.println(JsonbBuilder.create().toJson(nested)); // Output: {"a":{"b":{"c":123}}}
    }
}

Answer 1

You can just create both inner class A, B in Nested to reduce unnecessary hierarchy.

package com.example.demo;
package com.jason.empty;

import lombok.Data;

@Data
public class Nested {
    private A a;

    @Data
    public static class A {
        private B b;
    }

    @Data
    public static class B {
        private int c;
    }
}

Note here import com.example.demo.Nested.A so that you can just use A a = new A(); instead of Nested.A a = new Nested.A(); to reduce the complexity.

Jackson is a good JSON serialization/deserialization library for Java. The ObjectMapper API provides a straightforward way to parse and generate JSON:

package com.example.demo;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.example.demo.Nested.A;
import com.example.demo.Nested.B;

public class Main {
    public static void main(String[] args) throws Exception {
        B b = new B();
        b.setC(123);

        A a = new A();
        a.setB(b);

        Nested nested = new Nested();
        nested.setA(a);

        String json = new ObjectMapper().writeValueAsString(nested);
        System.out.println(json);   // Output: {"a":{"b":{"c":123}}}
    }
}

Moreover

You could use @Accessors(chain = true) to chain multiple set operations together in one statement.

import lombok.Data;
import lombok.experimental.Accessors;

@Data
@Accessors(chain = true)
public class Nested {
    private A a;

    @Data
    @Accessors(chain = true)
    public static class A {
        private B b;
    }

    @Data
    @Accessors(chain = true)
    public static class B {
        private int c;
    }
}

public static void main(String[] args) throws Exception {
    B b = new B().setC(123);
    A a = new A().setB(b);
    Nested nested = new Nested().setA(a);
    String json = new ObjectMapper().writeValueAsString(nested);
    System.out.println(json);  // Output: {"a":{"b":{"c":123}}}
}