试试这个：

class Test {
    public static void main(String[] args) throws Exception {
        Method method = MyClass.class.getDeclaredMethod("getId", Object.class);
        method.setAccessible(true);
        System.out.println(method.invoke(null, 123L));
        //System.out.println(MyClass.getId("")); // 'getId(java.lang.String)' has private access in 'MyClass'
    }
}

class MyClass {
    private static <T> String getId(T element) {
        return String.valueOf(element);
    }
}

输出：

123