在Java中解析JSON Map时出现NullPointer异常

Question

我正在尝试在REST API中从下面的JSON解析productId，名称和价格-但是尝试获取他时我得到了空指针异常name- String name = (String) obj.get("name");，我可以知道我在做什么错吗？

任何帮助将非常感激。谢谢！

JSON：

{
    "id": "af0b86eb-046c-4400-8bc4-0e26042b8f53",
    "products": [{
            "productId": "1234",
            "name": "apple",
            "price": "383939"
        }
    ]
}

Controller.java

public ResponseEntity<Object> create(@RequestBody Map<String, Object> obj) {
    Product response = myservice.create(obj);
    return new ResponseEntity<Object>(response, HttpStatus.CREATED);
}

Service.java

public Product create(Map<String, Object> obj) { 
    for (Entry<String, Object> entry : obj.entrySet()) {
        System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
    }       

    Object [] products = (Object[]) obj.get("products");
    HashMap <String, Object> productOne = (HashMap) products[0];
    String productId = (String) productOne.get("name");
    System.out.println("productId: " +productId);

    String name = (String) obj.get("name");
    System.out.println("name: " +name);
}

输出：

Key : products Value : [{productId=1234, name=apple, price=383939}]

Answer 1

通过obj.get("name")，您尝试name从json请求的顶层通过键获取值，而这是第二层对象的属性

在伪代码（跳过转换和空检查）中，它应如下所示： obj.get("products")[0].get("name")