如何從列表中獲取typeArguments <T> 由object.getClass（）。getDeclaredField（“ fieldname”）。getGenericType（）返回；

Question

我正在處理此問題大約2天，但仍然無法解決。 我有這個方法：

public List<T> findByKeyValue(String key, String value, Object t) {
    Field field;
    Class<?> clazz = t.getClass();

    field = clazz.getDeclaredField(key);
    Type type = field.getType();

    if(type.equals(List.class)) {

        // HERE IS THE PROBLEM, the value of "field" is "public java.util.List com.cacobr.model.Video.categoryCollection" and categoryCollection is a List <Category>
        // **I need to get the class "Category" with Reflection**
        // The "field.getGenericType()" command returns "java.util.List <com.cacobr.model.Category>"
        // If I could use something like ".getActualTypeArguments()[0]" could return the class "Category" but I can't use this method after a "getGenericType()"

    ....
    }

我可以上課類別嗎？

Answer 1

您應該可以將其轉換為ParameterizedType ：

Type type = field.getGenericType();
if (type instanceof ParameterizedType) {
    ParamterizedType pt = (ParameterizedType) type;
    if (pt.getRawType() == List.class &&
        pt.getActualTypeArguments()[0] == Category.class) {
        ...
    }
}