How to solve 'Expected BEGIN_OBJECT but was BEGIN_ARRAY' error in Java using Gson?

反序列化时，Gson 可以期望一个 JSON 对象，但它可以找到一个 JSON 数组。由于它无法从一种转换为另一种，因此它可能会在运行时抛出错误“JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY”。

示例

import com.google.gson.Gson;
public class GsonErrorTest {
   public static void main(String args[]) throws Exception {
      String json = "{\"employee\":[{\"name\":\"Raja Ramesh\", \"technology\":\"java\"}]}";
      Gson gson = new Gson();
      Software software = gson.fromJson(json, Software.class);
      System.out.println(software);
   }
}
class Software {
   Employee employee;
}
class Employee {
   String name;
   String technology;
}

输出

Exception in thread "main"<strong> </strong>com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 14
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:176)at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172)at com.google.gson.Gson.fromJson(Gson.java:795)
at com.google.gson.Gson.fromJson(Gson.java:761)
at com.google.gson.Gson.fromJson(Gson.java:710)
at com.google.gson.Gson.fromJson(Gson.java:682)
at BeginObjectError.main(BeginObjectError.java:7)
Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 14
at com.google.gson.stream.JsonReader.expect(JsonReader.java:339)
at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:322)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:165)

我们需要通过将 POJO 类型更改为 集合或数组来解决此问题类型。 在下面的示例中，我们可以在 POJO 类中使用List集合。

示例

import java.util.List;
import com.google.gson.Gson;
public class GsonListTest {
   public static void main(String args[]) throws Exception {
      String jsonString = "{\"employees\":[{\"name\":\"Raja Ramesh\", \"technology\":\"Java\"}]}";
      Gson gson = new Gson();
      Software software = gson.fromJson(jsonString, Software.class);
      System.out.println(software);
   }
}
class Software {
   List<Employee> employees;
   @Override
   public String toString() {
      return "Software [employees=" + employees + "]";
   }
}
class Employee {
   String name;
   String technology;
   @Override
   public String toString() {
      return "Employee [name=" + name + ", technology=" + technology + "]";
   }
}

输出

Software [employees=[Employee [name=Raja Ramesh, technology=Java]]]

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