Question

我有这样的设置：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "dishName", defaultImpl = Food.class)
@JsonSubTypes(value = {
    @Type(name = "fries", value = Fries.class),
    @Type(name = "burger", value = Burger.class)
})
public class Food {
  private String dishName;

  @Override
  public String toString() {
    return dishName + ", type: " + this.getClass().getName();
  }
}

public class Fries extends Food { /*...*/ }

public class Burger extends Food { /*...*/ }

public class TryItOut {

  private static String foodString = "[ { \"dishName\":\"burger\" }, { \"dishName\":\"fries\" }, { \"dishName\":\"cabbage\" } ]";

  public static void main(String[] args) {
    ObjectMapper m = new ObjectMapper();
    try {
        Food[] food = m.readValue(foodString, Food[].class);
        for (Food dish : food) {
            System.out.println(dish);
        }
    } catch (IOException e) {
        System.out.println("something went wrong");
        e.printStackTrace();
    }
  }
}

我想用它来反序列化我无法影响的json内容（所以没有选择添加＆＃34;正确的＆＃34;类型信息）。我遇到的问题是显然dishName json属性用于确定子类型，但它没有反序列化到java字段中。有没有办法实现这一目标？换句话说：main方法打印

null, type: Burger
null, type: Fries
null, type: Food

在控制台上

，但我希望它打印

burger, type: Burger
fries, type: Fries
cabbage, type: Food

这特别令人讨厌，因为我后来无法找到最后一个对象是卷心菜。这使得默认实现的好处无效。

编辑：

@Evil Raat的答案就是诀窍。为了完整起见：dishName类中的Food字段需要@JsonProperty注释才能使用此示例。因此，工作示例如下所示：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "dishName", defaultImpl = Food.class, visible = true)
@JsonSubTypes(value = {
    @Type(name = "fries", value = Fries.class),
    @Type(name = "burger", value = Burger.class)
})
public class Food {

  @JsonProperty
  private String dishName;

  @Override
  public String toString() {
    return dishName + ", type: " + this.getClass().getName();
  }
}

public class Fries extends Food { /*...*/ }

public class Burger extends Food { /*...*/ }

public class TryItOut {

  private static String foodString = "[ { \"dishName\":\"burger\" }, { \"dishName\":\"fries\" }, { \"dishName\":\"cabbage\" } ]";

  public static void main(String[] args) {
    ObjectMapper m = new ObjectMapper();
    try {
        Food[] food = m.readValue(foodString, Food[].class);
        for (Food dish : food) {
            System.out.println(dish);
        }
    } catch (IOException e) {
        System.out.println("something went wrong");
        e.printStackTrace();
    }
  }
}

Answer 1

要维护用于反序列化的属性的值，只需在@JsonSubTypes注释上将visible属性设置为true：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "dishName", defaultImpl = Food.class, visible = true)

在使用Jackson的@JsonTypeInfo进行反序列化时，如何保留type属性？

1 个答案: