使用JSON的Jackson :接收"null“对象

Question

我需要将优步产品JSON响应从这里转换为Java。我使用Jackson来处理JSON。我的输入JSON看起来像：

    {
      "products": [
        {
           "capacity": 2,
           "description": "Ride for less with uberPOOL",
           "price_details": {},
           "image": "http://d1a3f4spazzrp4.cloudfront.net/car.jpg",
           "display_name": "POOL",
           "product_id": "26546650-e557-4a7b-86e7-6a3942445247",
           "shared": true,
        },
        {
           "capacity": 4,
           "description": "The low-cost Uber",
           "price_details": {
              "distance_unit": "mile",
              "cost_per_minute": 0.26,
              "service_fees": [
                 {
                    "fee": 1.0,
                    "name": "Safe Rides Fee"
                 }
              ],
              "minimum": 5.0,
              "cost_per_distance": 1.3,
              "base": 2.2,
              "cancellation_fee": 5.0,
              "currency_code": "USD"
           },
           "cash_enabled": false,
           "image": "http://d1a3f4spazzrp4.cloudfront.net/car.jpg",
           "display_name": "uberX",
           "product_id": "a1111c8c-c720-46c3-8534-2fcdd730040d",
           "shared": false
        }
      ]
    }

我的实体类看起来像：

    public class Products {

        @JsonProperty
        private int capacity;
        @JsonProperty
        private String description;
        @JsonProperty
        private String price_details;
        @JsonProperty
        private String image; 
        @JsonProperty
        private Boolean cash_enabled; 
        @JsonProperty
        private Boolean shared; 
        @JsonProperty
        private String short_description; 
        @JsonProperty
        private String display_name;

            //getter, setter methods
    } 

包装类如下所示：

    public class ProductsModel{
        private List <Products> product;

        public List<Products> getProduct() {
            return product;
        }
        public void setProduct(List<Products> product) {
            this.product = product;
        }
    }

现在，当我尝试将JSON映射到我的wapper类并尝试打印产品时。它给了“空”不知道为什么..。请帮忙指出原因。

    private ObjectMapper mapper = new ObjectMapper();
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    productsModel = mapper.readValue(line1, ProductsModel.class);   
    response.getWriter().println("get products:" + productsModel.getProduct()); //<-- returns null - not sure why

Answer 1

使用下面的ProductsModel类可以很好地工作。

乘积实体：

public class Products {

    @JsonProperty
    private int capacity;

    @JsonProperty
    private String description;

    @JsonProperty
    private Map price_details;

    @JsonProperty
    private String image;

    @JsonProperty
    private Boolean cash_enabled;

    @JsonProperty
    private Boolean shared;

    @JsonProperty
    private String short_description;

    @JsonProperty
    private String display_name;
}

ProductsModel包装器类：

public class ProductsModel {

    private List<Products> products;

    public List<Products> getProducts() {
        return products;
    }

    public void setProducts(List<Products> products) {
        this.products = products;
    }
}

在您的代码中有两个错误：

1. json中的PriceDetails price_details值是一个对象，而不是字符串，因此它应该是一个映射或一些包含price_details json中可用属性的实体类。在我的回复中，我只是使用了Map。
2. ProductsModel包装器类中密钥的名称是products，它应该是products。

我刚刚在ProductsModel类中进行了更改，它运行得很好。