如何將枚舉序列化為 Object 形狀和默認字符串？

Question

對於具有屬性的枚舉，例如：

public enum Thing {
  THING_A("a"),
  THING_B("b");

  private String thing;

  private Thing(String thing) {
    this.thing = thing;
  }

  // Getters...
}

Jackson序列化為值的名稱，例如：

mapper.writeValueAsString(Thing.THING_A)); // "THING_A"

如果我們添加注釋以將序列化視為 object：
@JsonFormat(shape = JsonFormat.Shape.OBJECT)它將序列化屬性：

mapper.writeValueAsString(Thing.THING_A)); // "{"thing":"a"}"

我希望能夠在序列化期間決定使用哪些方法。 因為這跨越了大量的枚舉，我寧願不編輯每一個。 有沒有好的方法來做到這一點？

例如：這樣的事情會很棒：

mapper.writeValueAsString(Thing.THING_A, JsonFormat.Shape.OBJECT); // "{"thing":"a"}"
mapper.writeValueAsString(Thing.THING_A, JsonFormat.Enum.DEFAULT); // "THING_A"

Answer 1

上面的問題是類似的，已經回答了。 Jackson ObjectMapper 設置 JsonFormat.Shape.ARRAY 無注釋。

您可以使用特定於 Enum 的自定義 object 映射器和其他類的不同 object 映射器。

Answer 2

Since, com.fasterxml.jackson.annotation.JsonFormat is an annotation you can implement your own com.fasterxml.jackson.databind.AnnotationIntrospector and return value you want for all your enums. 您可以在下面找到簡單的示例：

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.introspect.Annotated;
import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;

public class JsonPathApp {

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setAnnotationIntrospector(AnnotationIntrospector.pair(new DynamicEnumAnnotationIntrospector(), new JacksonAnnotationIntrospector()));

        System.out.println(mapper.writeValueAsString(Thing.THING_A));
    }
}

class DynamicEnumAnnotationIntrospector extends AnnotationIntrospector {

    @Override
    public Version version() {
        return new Version(1, 0, 0, "Dynamic enum object", "your.package", "jackson.dynamic.enum");
    }

    @Override
    public JsonFormat.Value findFormat(Annotated memberOrClass) {
        final Class<?> rawType = memberOrClass.getRawType();
        if (rawType.isEnum() && rawType.getPackage().getName().startsWith("your.package")) {
            return JsonFormat.Value.forShape(JsonFormat.Shape.OBJECT);
        }

        return super.findFormat(memberOrClass);
    }
}

上面的代碼打印：

{"thing":"a"}

現在，您可以創建兩個ObjectMapper實例，一個配置您自己的注釋內省，第二個保留默認值。 如果您真的想以動態方式使用它，您可以為每個可用的Shape值創建一個ObjectMapper ，並且 select 需要一個給定形狀：

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonFormat.Shape;
import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.introspect.Annotated;
import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;

import java.util.Arrays;
import java.util.EnumMap;
import java.util.List;
import java.util.Objects;

public class JsonPathApp {

    public static void main(String[] args) throws Exception {
        JsonFactory factory = new JsonFactory();

        for (Shape shape : Shape.values()) {
            ObjectMapper mapper = factory.getWithEnumShapeSetTo(shape);
            System.out.println(shape + " => " + mapper.writeValueAsString(Thing.THING_A));
        }
    }
}

class JsonFactory {
    private final AnnotationIntrospector defaultIntrospector = new JacksonAnnotationIntrospector();
    private final EnumMap<Shape, ObjectMapper> instances = new EnumMap<>(Shape.class);

    public JsonFactory() {
        final List<Shape> notAllowed = Arrays.asList(Shape.BOOLEAN, Shape.BINARY);
        Arrays.stream(Shape.values())
                .filter(shape -> !notAllowed.contains(shape))
                .forEach(shape -> instances.put(shape, createNewWithEnumShape(shape)));
    }

    private ObjectMapper createNewWithEnumShape(Shape shape) {
        DynamicEnumAnnotationIntrospector enumIntrospector = new DynamicEnumAnnotationIntrospector(shape);

        ObjectMapper mapper = new ObjectMapper();
        mapper.setAnnotationIntrospector(AnnotationIntrospector.pair(enumIntrospector, defaultIntrospector));

        return mapper;
    }

    public ObjectMapper getWithEnumShapeSetTo(Shape shape) {
        Objects.requireNonNull(shape);

        final ObjectMapper mapper = instances.get(shape);
        if (mapper == null) {
            return new ObjectMapper();
        }

        return mapper;
    }
}

class DynamicEnumAnnotationIntrospector extends AnnotationIntrospector {

    private final Shape shape;

    public DynamicEnumAnnotationIntrospector(Shape shape) {
        this.shape = Objects.requireNonNull(shape);
    }

    @Override
    public Version version() {
        return new Version(1, 0, 0, "Dynamic enum shape", "your.package", "jackson.dynamic.enum");
    }

    @Override
    public JsonFormat.Value findFormat(Annotated memberOrClass) {
        final Class<?> rawType = memberOrClass.getRawType();
        if (rawType.isEnum() && rawType.getPackage().getName().startsWith("your.package")) {
            return JsonFormat.Value.forShape(shape);
        }

        return super.findFormat(memberOrClass);
    }
}

上面的代碼打印：

ANY => "THING_A"
NATURAL => "THING_A"
SCALAR => "THING_A"
ARRAY => 0
OBJECT => {"thing":"a"}
NUMBER => 0
NUMBER_FLOAT => 0
NUMBER_INT => 0
STRING => "THING_A"
BOOLEAN => "THING_A"
BINARY => "THING_A"

上面的代碼當然是矯枉過正，但我想展示我們擁有的可能性。 我們只有 3 個不同的輸出，因此您可以使用相同的 output 對值進行分組，並創建最多 3 個不同的ObjectMappers 。