杰克逊json序列化列表列表的特定属性值

Question

Good day everyone, I would like to remove a property and a property name of an object which is in a List<> when returned from another object (as property).

I have the following classes:

public class Base {
    protected String type;

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }
}

public class A extends Base {
    private double[] value;

    public A() { type = "A"; }

    public A(double[] value) {
        this();
        setValue(value);
    }

    public double[] getValue() {
        return value;
    }

    public void setValue(double[] value) {
        this.value = value;
    }
}

public class B extends Base {
    private List<A> value = new ArrayList<A>();

    public B() { type = "B"; }

    public B(List<A> value) {
        this();
        setValue(value);
    }

    public List<A> getValue() { return value; }

    public void setValue(List<A> value) {
        this.value = value;
    }
}

public class C extends Base {
    private List<B> value = new ArrayList<B>();

    public C() { type = "C"; }

    public List<B> getValue() {
        return value;
    }

    public void setValue(List<B> value) {
        this.value = value;
    }
}

And use them like:

A a = new A();
a.setValue(new double[]{1,2});

B b = new B();
List<A> aList = new ArrayList<A>();
aList.add(new A(new double[]{1,2}));
aList.add(new A(new double[]{3,4}));
b.setValue(aList);

C c = new C();
List<B> bList = new ArrayList<B>();
List<A> aList1 = new ArrayList<A>();
List<A> aList2 = new ArrayList<A>();
aList1.add(new A(new double[]{1,2}));
aList1.add(new A(new double[]{3,4}));
aList2.add(new A(new double[]{5,6}));
bList.add(new B(aList1));
bList.add(new B(aList2));
c.setValue(bList);

ObjectMapper jsonMapper = new ObjectMapper();
jsonMapper.enable(SerializationFeature.INDENT_OUTPUT);

try {
    System.out.println("=== com.example.A ===");
    System.out.println(jsonMapper.writeValueAsString(a));

    System.out.println("=== com.example.B ===");
    System.out.println(jsonMapper.writeValueAsString(b));

    System.out.println("=== com.example.C ===");
    System.out.println(jsonMapper.writeValueAsString(c));
} catch (JsonProcessingException e) {
    e.printStackTrace();
}

Where I get:

=== com.example.A ===
{
  "type" : "A",
  "value" : [ 1.0, 2.0 ]
}
=== com.example.B ===
{
  "type" : "B",
  "value" : [ {
    "type" : "A",
    "value" : [ 1.0, 2.0 ]
  }, {
    "type" : "A",
    "value" : [ 3.0, 4.0 ]
  } ]
}
=== com.example.C ===
{
  "type" : "C",
  "value" : [ {
    "type" : "B",
    "value" : [ {
      "type" : "A",
      "value" : [ 1.0, 2.0 ]
    }, {
      "type" : "A",
      "value" : [ 3.0, 4.0 ]
    } ]
  }, {
    "type" : "B",
    "value" : [ {
      "type" : "A",
      "value" : [ 5.0, 6.0 ]
    } ]
  } ]
}

But I want to have it like:

=== com.example.A ===
{
  "type" : "A",
  "value" : [ 1.0, 2.0 ]
}
=== com.example.B ===
{
  "type" : "B",
  "value" : [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ]
}
=== com.example.C ===
{
  "type" : "C",
  "value" : [ [ [ 1.0, 2.0 ], [ 3.0, 4.0 ] ], [ [ 5.0, 6.0 ] ] ]
}

I was able to remove the property "type" of A when returned from B and property "type" of B from C using:

    @JsonIgnoreProperties( { "type" })
    public List<A> getValue() {
        return value;
    }
...
    @JsonIgnoreProperties( { "type" })
    public List<B> getValue() {
        return value;
    }

But I'm still getting the property "value" name and the curly braces...

=== com.example.A ===
{
  "type" : "A",
  "value" : [ 1.0, 2.0 ]
}
=== com.example.B ===
{
  "type" : "B",
  "value" : [ {
    "value" : [ 1.0, 2.0 ]
  }, {
    "value" : [ 3.0, 4.0 ]
  } ]
}
=== com.example.C ===
{
  "type" : "C",
  "value" : [ {
    "value" : [ {
      "value" : [ 1.0, 2.0 ]
    }, {
      "value" : [ 3.0, 4.0 ]
    } ]
  }, {
    "value" : [ {
      "value" : [ 5.0, 6.0 ]
    } ]
  } ]
}

What annotation can I use to get the desired output? Or do I have to redesign my classes?

Answer 1

public class A extends Base {
    private double[] value;

    public A() {
        type = "A";
    }

    public A(double[] value) {
        this();
        setValue(value);
    }

    public double[] getValue() {
        return value;
    }

    public void setValue(double[] value) {
        this.value = value;
    }
}

public class B extends Base {

    private List<A> value = new ArrayList<A>();

    public B() {
        type = "B";
    }

    public B(List<A> value) {
        this();
        setValue(value);
    }

    @JsonIgnoreProperties({"type"})
    public List<A> getValue() {
        return value;
    }

    @JsonGetter("value")
    @JsonIgnoreProperties({"type"})
    public List<double[]> getA() {
        List<double[]> res = new ArrayList<>();
        for (A a : value) {
            res.add(a.getValue());
        }
        return res;
    }

    public void setValue(List<A> value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "" + value;
    }
}

public class C extends Base {
    private List<B> value = new ArrayList<B>();

    public C() {
        type = "C";
    }

    @JsonGetter("value")
    @JsonIgnoreProperties({"type"})
    public List<List<double[]>> getB() {
        List<List<double[]>> res1 = new ArrayList<>();            
        for (B b : value) {
            List<double[]> res2 = new ArrayList<>();
            for (A a : b.getValue()) {
                res2.add(a.getValue());
            }
            res1.add(res2);
        }
        return res1;
    }

    public List<B> getValue() {
        return value;
    }

    public void setValue(List<B> value) {
        this.value = value;
    }
}

Answer 2

Modify the B and C classes as below:

Added @JsonIgnore annotation to value to avoid value being printed and created a new method getValueForJson() with return type List<double[]> whose output is a deep parsed result with values of class A . This new method is added with annotation @JsonProperty with value as "value" so as to get this treated as a member named value .

class B extends Base {
    @JsonIgnore
    private List<A> value = new ArrayList<A>();

    public B() {
        type = "B";
    }

    public B(List<A> value) {
        this();
        setValue(value);
    }

    public List<A> getValue() {
        return value;
    }

    public void setValue(List<A> value) {
        this.value = value;
    }

    @JsonProperty("value")
    public List<double[]> getValueForJson(){
        List<double[]> res = new ArrayList<double[]>();
        value.forEach(a -> res.add(a.getValue()));
        return res;
    }
}

class C extends Base {
    @JsonIgnore
    private List<B> value = new ArrayList<B>();

    public C() {
        type = "C";
    }

    public List<B> getValue() {
        return value;
    }

    public void setValue(List<B> value) {
        this.value = value;
    }

    @JsonProperty("value")
    public List<double[]> getValueForJson(){
        List<double[]> res = new ArrayList<double[]>();
        value.forEach(b -> b.getValue().forEach(a -> res.add(a.getValue())));
        return res;
    }
}