从 json 中提取字段值

Question

我正在尝试从 json 中提取字段的值，我有一个 json 文件，其内容如下：

 [ {
    "autoId": "babsds",
    "partNumber": 6144686,
    "amount": "139.98",
    "id": "1129"
  },
  {
    "autoId": "bassb",
    "partNumber": 6442686,
    "amount": "139.98",
    "id": "1219"
  },
  {
    "autoId": "bsswab",
    "partNumber": 6344686,
    "amount": "139.98",
    "id": "1291"
  },
  {
    "autoId": "badfgb",
    "partNumber": 6446856,
    "amount": "139.98",
    "id": "0129"
  }]

为了提取 id 字段的值，我使用以下代码创建了一个 java 类：

  Gson gson1 = new Gson();
    Type listType = new TypeToken<ArrayList<MyObject>>(){}.getType();

    List<MyObject> stats = gson1.fromJson(getJson(), listType);
    for (MyObject st : stats) {
        System.out.println(st.id);
    }

并且还创建了一个 MyObject 类：

    class MyObject {
       String autoId;
       String partNumber;
       String amount;
       String id;

       @Override
       public String toString() {
          return "MyObject [autoId=" + autoId + ", partNumber=" + partNumber + 
                  ", amount=" + amount +
                  ", id=" + id +
                  "]";
    }

但我得到了这个错误 ：

    Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $
      at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350)
      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:80)
      at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
      at com.google.gson.Gson.fromJson(Gson.java:888)
      ... 27 more

Answer 1

这是一个好的 JSON 格式化程序 真正可以提供帮助的地方。

{
    "autoId": "babsds",
    "partNumber": 6144686,
    "amount": "139.98",
    "id": "1129"
},
{
    "autoId": "bassb",
    "partNumber": 6442686,
    "amount": "139.98",
    "id": "1219"
},
{
    "autoId": "bsswab",
    "partNumber": 6344686,
    "amount": "139.98",
    "id": "1291"
},
{
    "autoId": "badfgb",
    "partNumber": 6446856,
    "amount": "139.98",
    "id": "0129"
}

无效，因为它应该以单个“外部”对象或数组开头

而且...

{
    [
        {
            "autoId": "babsds",
            "partNumber": 6144686,
            "amount": "139.98",
            "id": "1129"
        },
        {
            "autoId": "bassb",
            "partNumber": 6442686,
            "amount": "139.98",
            "id": "1219"
        },
        {
            "autoId": "bsswab",
            "partNumber": 6344686,
            "amount": "139.98",
            "id": "1291"
        },
        {
            "autoId": "badfgb",
            "partNumber": 6446856,
            "amount": "139.98",
            "id": "0129"
        }
    ]
}

无效，因为数组需要一个键，即 {"some array":[...]}

所以，我修改了你的 JSON 看起来像...

[
    {
        "autoId": "babsds",
        "partNumber": 6144686,
        "amount": "139.98",
        "id": "1129"
    },
    {
        "autoId": "bassb",
        "partNumber": 6442686,
        "amount": "139.98",
        "id": "1219"
    },
    {
        "autoId": "bsswab",
        "partNumber": 6344686,
        "amount": "139.98",
        "id": "1291"
    },
    {
        "autoId": "badfgb",
        "partNumber": 6446856,
        "amount": "139.98",
        "id": "0129"
    }
]

并使用...

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        Gson gson1 = new Gson();
        Type listType = new TypeToken<ArrayList<MyObject>>() {
        }.getType();

        List<MyObject> stats = gson1.fromJson(getJson(), listType);
        for (MyObject st : stats) {
            System.out.println(st.id);
        }
    }

    protected static String getJson() {
        return """
            [
                {
                    "autoId": "babsds",
                    "partNumber": 6144686,
                    "amount": "139.98",
                    "id": "1129"
                },
                {
                    "autoId": "bassb",
                    "partNumber": 6442686,
                    "amount": "139.98",
                    "id": "1219"
                },
                {
                    "autoId": "bsswab",
                    "partNumber": 6344686,
                    "amount": "139.98",
                    "id": "1291"
                },
                {
                    "autoId": "badfgb",
                    "partNumber": 6446856,
                    "amount": "139.98",
                    "id": "0129"
                }
            ]
               """;
    }

    public static class MyObject {
        String autoId;
        String partNumber;
        String amount;
        String id;

        @Override
        public String toString() {
            return "MyObject [autoId=" + autoId + ", partNumber=" + partNumber
                    + ", amount=" + amount
                    + ", id=" + id
                    + "]";
        }
    }
}

来解析它并打印...

1129
1219
1291
0129