Jackson-jr 读取多态 ArrayList

Question

我正在使用 Jackson-jr 来读取我的 JSON 文件。其中一个有点复杂：

[
 {"test-1":["a","b","c","d"]},
 {"test-2":["b","j","d"]},
 {"test-3":["n","e","o","p","i"]},
 {"test-4":["s","a","v","z","b","ç","x","p"]},
 {"test-5":["d","q","u"]},
 {"test-6":["f","b"]}
]

我的代码很简单：

InputStream inputStream   = assetManager.open("test.json");
ArrayList<HashMap<String, ArrayList<String>>> arrays = JSON.std.beanFrom(ArrayList.class, inputStream);

我的目的是让每个数组都能与它们一起工作：

arrays.get(i);

但是，当执行此行时，我有一个异常：

Caused by: java.lang.ClassCastException: com.fasterxml.jackson.jr.ob.impl.DeferredMap cannot be cast to java.util.HashMap

Jackson-jr 没有 TypeFactory、TypeReference 或 ObjectMapper。我为jackson找到了一些链接，而不是jackson-jr：

ClassCastException when convert json to list of objects

Jackson custom deserializer for one field with polymorphic types

Tricky(?) JSON, polymorphic deserialization

Jackson-Jr 有处理这个问题的说法吗？

Answer 1

您应该对接口而不是实现类进行编程。由于返回的 Map 实现是 DeferredMap 而不是 HashMap，因此您会得到 ClassCastException。如下更改分配

List<Map<String, List<String>>> arrays = JSON.std.beanFrom(ArrayList.class, inputStream);