Java：使用反射实例化枚举
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Java: instantiating an enum using reflection
提问by dagnelies
Suppose you have a text file like:
假设您有一个文本文件，例如：
my_setting = ON
some_method = METHOD_A
verbosity = DEBUG
...
That you wish to to update a corresponding object accordingly:
您希望相应地更新相应的对象：
Setting my_setting = ON;
Method some_method = METHOD_A;
Verbosity verbosity = DEBUG;
...
Where all are different kind of enums.
所有都是不同类型的枚举。
I would like to have a generic way to instantiate the enum values. That is, at runtime using reflection, and without knowing the enum types of the object in advance.
我想要一种通用的方法来实例化枚举值。也就是说，在运行时使用反射，并且事先不知道对象的枚举类型。
I would have imagined something like this:
我会想象这样的事情：
for (ConfigLine line : lines)
{
String[] tokens = line.string.split("=", 2);
String name = tokens[0].trim();
String value = tokens[1].trim();
try
{
Field field = this.getClass().getDeclaredField(name);
if(field.getType().isEnum())
{
// doesn't work (cannot convert String to enum)
field.set(this, value);
// invalid code (some strange generics issue)
field.set(this, Enum.valueOf(field.getType().getClass(), value));
}
else
{ /*...*/ }
}
catch //...
}
The question is: what should there be instead? Is it even possible to instantiate an unknown enum given its String representation?
问题是：取而代之的是什么？鉴于其字符串表示形式，甚至可以实例化未知枚举吗？
采纳答案by Bozho
field.set(this, Enum.valueOf((Class<Enum>) field.getType(), value));
getClass()aftergetType()should not be called - it returns the class of aClassinstance- You can cast
Class<Enum>, to avoid generic problems, because you already know that theClassis anenum
getClass()aftergetType()不应该被调用 - 它返回一个Class实例的类- 您可以强制转换
Class<Enum>, 以避免一般性问题，因为您已经知道Class是enum
回答by Matthew Flaschen
You have an extra getClasscall, and you have to cast (more specific cast per Bozho):
你有一个额外的getClass电话，你必须施法（每个 Bozho 更具体的施法）：
field.set(test, Enum.valueOf((Class<Enum>) field.getType(), value));
回答by ThiamTeck
You may code your Enum similar tho this:
您可以对您的 Enum 进行类似的编码：
public enum Setting {
ON("ON"),OFF("OFF");
private final String setting;
private static final Map<String, Setting> stringToEnum = new ConcurrentHashMap<String, Setting>();
static {
for (Setting set: values()){
stringToEnum.put(set.setting, set);
}
}
private Setting(String setting) {
this.setting = setting;
}
public String toString(){
return this.setting;
}
public static RequestStatus fromString(String setting){
return stringToEnum.get(setting);
}
}
Then you may easily create Enum from String without reflection:
然后您可以轻松地从 String 创建 Enum 而无需反射：
Setting my_settings = Setting.fromString("ON");
This solution is not originated from myself. I read it from somewhere else, but I can't recall the source.
这个解决方案不是来自我自己。我是从别处读到的，但我想不起来出处了。
回答by Rebzie
Alternative solution with no casting
没有铸造的替代解决方案
try {
Method valueOf = field.getType().getMethod("valueOf", String.class);
Object value = valueOf.invoke(null, param);
field.set(test, value);
} catch ( ReflectiveOperationException e) {
// handle error here
}
回答by Dev Vercer
The accepted answer results in warnings because it uses the raw type Enum instead of Enum<T extends Enum<T>>.
接受的答案会导致警告，因为它使用原始类型 Enum 而不是 Enum<T extends Enum<T>>。
To get around this you need to use a generic method like this:
要解决这个问题，您需要使用这样的通用方法：
@SuppressWarnings("unchecked")
private <T extends Enum<T>> T createEnumInstance(String name, Type type) {
return Enum.valueOf((Class<T>) type, name);
}
Call it like this:
像这样调用它：
Enum<?> enum = createEnumInstance(name, field.getType());
field.set(this, enum);
