所有操作都是通过子类Dao实例操作，子类实例可以通过继承获取自父类AbstractDao的泛型类型

private Class<T> getParameterizedType() {
    Type type = getClass().getGenericSuperclass();
    if (!(type instanceof ParameterizedType)) {
        throw new IllegalArgumentException("Class " + getClass().getName() + " does not have parameterized type.");
    }
    Type[] types = ((ParameterizedType) type).getActualTypeArguments();
    if (types.length != 1) {
        throw new IllegalArgumentException("Class " + getClass().getName() + " has more than 1 parameterized types.");
    }
    Type r = types[0];
    if (!(r instanceof Class<?>)) {
        throw new IllegalArgumentException("Class " + getClass().getName() + " does not have parameterized type of class.");
    }
    return (Class<T>) r;
}