在访问嵌套json时遇到问题。类似的东西：

[
{
 key-value,
 key-value
},
{
 key-value,
 key-value
},
{
 key-value,
 key-value
}
]

效果很好，但当我尝试时：

{
  "alfa":{
      "id":"foo",
      "product":{
          "id":"foo1",
          "price":"foo2"
      }
  },
 "beta":{
      "id":"foo",
      "product":{
          "id":"foo1",
          "price":"foo2"
      }
  }
}

我得到一个错误：
com.fasterxml.jackson.databind.exc.mismatchedinputexception:无法反序列化'java.util.arraylist<。。。
我当然改变了班级结构：

public class Alphabet{
   private Purchase purchase;
...

public class Purchase{
   private String id;
   private Product product;
...

public class Product {
   private String id;
   private String price;
...

阅读：

ObjectMapper mapper = new ObjectMapper();
InputStream inputStream = new FileInputStream(new File("src/main/json/file.json"));
TypeReference<List<Alphabet>> typeReference = new TypeReference<List<Alphabet>>() {};
List<Alphabet> alphabet= mapper.readValue(inputStream, typeReference);
System.out.println(alphabet);

请问怎么了？