英文:
identifying substituted type of Collection using reflection
问题
我正在编写一个用于自动生成测试数据的小型库。它使用反射来创建任何类的随机实例。当其中一个类具有 List<T> 类型的字段时，我遇到了问题。我该如何找出 T 的类型？
在 IntelliJ 的“求值表达式”控制台中尝试了一些操作，我得出了以下结论：
private Class getGenericType(Field field){
return ((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0].getClass();
}
在弹出的控制台中，这似乎是有效的，但是当我将其放入代码并运行时，我收到了以下错误：
java.lang.InstantiationException: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
at java.base/java.lang.Class.newInstance(Class.java:571)
有什么想法吗？我是否走在正确的道路上？
英文:
I'm writing a little library for automatic generation of test data. It uses reflection to be able to create a randomized instance of any class. I ran in to issues when one of the classes had a field of type List<T>. How do i find out the type of T?
playing around in IntelliJ's "evaluate expression" console, i came up with the following:
private Class getGenericType(Field field){
return ((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0].getClass();
}
which in seemed to work when evaluating in the popup console, but when I put it into the code and run, i get
java.lang.InstantiationException: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl
at java.base/java.lang.Class.newInstance(Class.java:571)
any ideas? am I even on the right path?
答案1
得分: 1
数组的第一个元素已经是一个Class实例，所以你可以这样做：
private Class getGenericType(Field field){
return (Class)((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0];
}
编辑：这只在泛型类型是具体非泛型类型（例如List<String>）的情况下有效。对于更复杂的情况，你需要检查该类型是否可以实例化。请参考注释。
英文:
The first element of the array is already a Class instance so you can do this
private Class getGenericType(Field field){
return (Class)((ParameterizedType) field.getGenericType()).getActualTypeArguments()[0];
}
Edit: This would only work assuming the generic type is a concrete non-generic type as in List<String>. For more complex cases you will have to check if the type is one that can be instantiated. See comments.
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