java Jackson 使用枚举键、POJO 值反序列化为 Map
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Hymanson deserializing into Map with an Enum Key, POJO Value
提问by ecbrodie
I am trying to deserialize JSON into a Java POJO using Hymanson. Without giving away confidential information, here is an example stack trace when ObjectMapper's deserialization fails:
我正在尝试使用 Hymanson 将 JSON 反序列化为 Java POJO。在不泄露机密信息的情况下，以下是 ObjectMapper 的反序列化失败时的示例堆栈跟踪：
org.codehaus.Hymanson.map.JsonMappingException: Can not construct Map key of type com.example.MyEnum from String "coins": not a valid representation: Can not construct Map key of type com.example.MyEnum from String "coins": not one of values for Enum class
My JSON looks like this:
我的 JSON 如下所示：
"foo": {
"coins": null,
...
}
And the class I want to deserialize into has this field:
我想反序列化的类有这个字段：
private Map<MyEnum, MyPojo> foo;
And my enum type looks like this:
我的枚举类型如下所示：
public enum MyEnum {
COINS("coins"),
...
}
I do realize that I am trying to deserialize a null value. But I believe this should still work: the result of the deserialization should be equivalent to having a Map with foo.put(MyEnum.COINS, null), which is indeed a valid Java instruction. Help is much appreciated, thanks in advance.
我确实意识到我正在尝试反序列化一个空值。但我相信这应该仍然有效：反序列化的结果应该相当于有一个 Map with foo.put(MyEnum.COINS, null)，这确实是一个有效的 Java 指令。非常感谢帮助，提前致谢。
回答by StaxMan
In addition to one good solution presented (factory method), there are 2 other ways:
除了提出的一种好的解决方案（工厂方法）之外，还有另外两种方法：
- If 'MyEnum.toString()' would return "coins", you can make Hymanson use "toString()" over "name()"with
ObjectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING) - You could add some other method to return id to use, and mark that method with
@JsonValueannotation (you can actually use that ontoString()as well, instead of enabling above feature) -- if that annotation exists, value returned by that method is used as the id.
- 如果“MyEnum.toString()”会返回“硬币”，你可以让Hyman逊使用“toString()”而不是“name()”
ObjectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING) - 您可以添加一些其他方法来返回要使用的 id，并用
@JsonValue注释标记该方法（您实际上也可以使用它toString()，而不是启用上述功能）——如果该注释存在，则该方法返回的值用作ID。
回答by ecbrodie
GRR! Figured it out.
太棒了！弄清楚了。
Solution for me was to create a static method, annotated with @JsonCreator, in my enum that creates an instance of the enum, based on a String parameter. It looked like this:
对我来说，解决方案是@JsonCreator在我的枚举中创建一个用 , 注释的静态方法，该方法基于 String 参数创建枚举的实例。它看起来像这样：
@JsonCreator
public static MyEnum create(String str) {
// code to return an enum based on the String parameter
}
回答by hoaz
Provide a static factory method in your enumeration class that constructs enum by string and annotate it with @JsonCreator:
在您的枚举类中提供一个静态工厂方法，该方法通过字符串构造枚举并使用@JsonCreator 对其进行注释：
@JsonCreator
public static MyEnum fromValue(String v) {
for (MyEnum myEnum : values()) {
if (myEnum.text.equals(v)) {
return myEnum;
}
}
throw new IllegalArgumentException("invalid string value passed: " + v);
}
