映射到POJO的ObjectMapper返回Null

Question

我有一个简单的Json，格式如下：

{
  "products": [
    {
      "id": 1,
      "productSku": "123",
      "productInventory": "24"
    },
    {
      "id": 2,
      "productSku": "12350",
      "productInventory": "22"
    },
    {
      "id": 3,
      "productSku": "12351",
      "productInventory": "19"
    }
  ]
}

我正在通过本地主机URL捕获此Json，并尝试将其映射到在其他端口上运行的另一个Spring Boot应用程序中的POJO类。 与上述Json对应的POJO类为：

@JsonIgnoreProperties(ignoreUnknown = true)
@JsonRootName(value = "products")
public class Product {

    private Integer id;
    private String productSku;
    private String productInventory;

    //getters and setters omitted


}

以下是我的控制器，它处理了映射和绑定：

@ResponseBody
    @GetMapping("index")
    public String getIndex() throws JsonParseException, 
       JsonMappingException, IOException {

        URL ApiUrlJson = new URL("http://localhost:1990/product");

        ObjectMapper mapper = new ObjectMapper();

        Product product = mapper.readValue(ApiUrlJson, Product.class);
        System.out.println(product.getProductInventory());

        return "Processed!";
    }

当我运行应用程序和访问索引以获取某个变量的值时，输出始终为null，并且不确定是否丢失了什么？

Answer 1

您的JSON文件中有一个产品列表。 您正在反序列化具有3个字段的一个对象。 这些字段都不在产品下，但是您忽略缺少的字段。

尝试反序列化为包含产品列表的新类。 删除@JsonRootName

Answer 2

您正在尝试反序列化JSON数组。 另外，由于此变量的访问权限是私有的，因此请不要省略设置方法。 您可以参考下面的代码。 我已经检查了它，并且能够对其进行反序列化。

@JsonIgnoreProperties(ignoreUnknown = true)
class Product {

  private Integer id;
  private String productSku;
  private String productInventory;

  public Integer getId() {
    return id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  public String getProductSku() {
    return productSku;
  }

  public void setProductSku(String productSku) {
    this.productSku = productSku;
  }

  public String getProductInventory() {
    return productInventory;
  }

  public void setProductInventory(String productInventory) {
    this.productInventory = productInventory;
  }
}

class Products{

  private List<Product> products;

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

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

public class Main{

  public static void main(String[] args) throws Exception{
    String jsonString =
        "{\n"
            + "  \"products\": [\n"
            + "    {\n"
            + "      \"id\": 1,\n"
            + "      \"productSku\": \"123\",\n"
            + "      \"productInventory\": \"24\"\n"
            + "    },\n"
            + "    {\n"
            + "      \"id\": 2,\n"
            + "      \"productSku\": \"12350\",\n"
            + "      \"productInventory\": \"22\"\n"
            + "    },\n"
            + "    {\n"
            + "      \"id\": 3,\n"
            + "      \"productSku\": \"12351\",\n"
            + "      \"productInventory\": \"19\"\n"
            + "    }\n"
            + "  ]\n"
            + "}";

    ObjectMapper mapper = new ObjectMapper();
    Products products = mapper.readValue(jsonString, Products.class);
    // To just access list of ids
    List<Product> productsList= products.getProducts();
    List<Integer> productIds = new ArrayList<>();
    for(Product product : productsList){
      productIds.add(product.getId());
    }
    System.out.println(productIds);
    }
}

Answer 3

您有一个对象，并且该对象内部是对象列表。 即

@JsonIgnoreProperties(ignoreUnknown = true)
@JsonRootName(value = "products")
public class Products {
    private List<Product> products;

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

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


public class Product{
.....
}

ObjectMapper objectMapper = new ObjectMapper();
Products product = objectMapper.readValue("json here....", Products.class);
System.out.println(product.getProducts().size());