英文:
Write generic static method in enum base class that can extract subclass instance to do a Jackson conversion
问题
我有一些类似这样的枚举类型：
public static enum Thingie {
ABC("abc"), DEF("def");
private String messageValue;
@JsonValue
public String getMessageValue() { return messageValue; }
private Thingie(String messageValue) { this.messageValue = messageValue; }
}
这将允许 Jackson 正确地在字符串值和枚举类型之间进行编组和解组。
可能会有时候，我想直接将字符串值转换为枚举值。这就像内部的 "fromValue()" 方法，但不完全相同：
public static Thingie messageValueOf(String messageValue) {
ObjectMapper mapper = new ObjectMapper();
return mapper.convertValue(messageValue, Thingie.class);
}
我想将这个转换为一个通用方法，并将其放入一个基类中，同时还有 "messageValue" 属性和访问器。构造方法将改为只调用 "super(messageValue)"。显然，如果可以的话，我会将 "mapper" 移到类级别。
到目前为止，我只尝试将其编写为单个枚举类型中的通用方法。我甚至无法让它工作。我无法弄清楚如何从模板参数中提取类。我之前见过这个特定的问题，也有一些答案，但我无法完全让它工作，而且我想象在基类中尝试这样做会增加额外的复杂性。
英文:
I have some enum types that look like this:
public static enum Thingie {
ABC("abc"), DEF("def");
private String messageValue;
@JsonValue
public String getMessageValue() { return messageValue; }
private Thingie(String messageValue) { this.messageValue = messageValue; }
}
This will allow Jackson to properly marshal and unmarshal between string values and the enum type.
There may be times when I'd like to directly convert a string value to the enum value. This would be like the internal "fromValue()" method, but not quite the same:
public static Thingie messageValueOf(String messageValue) {
ObjectMapper mapper = new ObjectMapper();
return mapper.convertValue(messageValue, Thingie.class);
}
I would like to convert this into a generic method AND put it into a base class, along with the "messageValue" property and accessor. The constructor would change to just call "super(messageValue)". Obviously, if I could do that, I would move the "mapper" to class level.
At this point, I've only attempted to write this as a generic method in the single enum type. I can't even get that working. I can't figure out how to extract the class from the template parameter. I've seen this particular question before, and there have been some answers, but I couldn't quite get it to work, and I imagine trying to do this in the base class would add additional complexity.
答案1
得分: 1
让我们假设我理解了您的问题（如果我理解错了，请纠正我）。
> 构造函数将更改为只调用 "super(messageValue)"
枚举无法扩展类，因此您不能这样做。但是您可以创建一个接口/类，用于处理此类查询（非常简化的代码）：
interface Test {
ObjectMapper MAPPER = new ObjectMapper();
static <T extends Enum<T>> T getIt(String s, Class<T> clazz) {
return MAPPER.convertValue(s, clazz);
}
}
public static void main(String[] args) {
Thingie abc = Test.getIt("abc", Thingie.class);
System.out.println(abc.ordinal());
}
英文:
Let's assume I understood your problem (correct me if I am wrong).
> The constructor would change to just call "super(messageValue)"
An enum can not extend a class, so you can't do that. But you can create an interface/class which you will delegate to for such queries (very simplistic code):
interface Test {
ObjectMapper MAPPER = new ObjectMapper();
static <T extends Enum<T>> T getIt(String s, Class<T> clazz) {
return MAPPER.convertValue(s, clazz);
}
}
public static void main(String[] args) {
Thingie abc = Test.getIt("abc", Thingie.class);
System.out.println(abc.ordinal());
}
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