java方法转换List<string> 列出<t>其中 T 可以是 Integer 或 Long</t></string>

Question

Given a List<String> , how to write a method to convert to it to List<T> where T can be Integer or Long but this is available at runtime only. Here is the code that I could come up with. It seems to work.

Is this the right way to do it?
Can it be simplified further?

public static void main(String[] args) {
    String s = "1, 2, 3, 4";
    System.out.println(convertCSVStringToList(s, Integer.class));
    System.out.println(convertCSVStringToList(s, Long.class));
}

public static <T> List<T> convertCSVStringToList(String s, Class<T> type) {
    return Stream.of(s.split(","))
        .map(String::trim)
        .map(e -> valueOf(e, type))
        .collect(Collectors.toList());
}


private static <T> T valueOf(String s, Class<T> type) {
    T t = null;

    try {
        if (type.equals(Integer.class)) {
            t = (T) Integer.valueOf(s);
        } else if (type.equals(Long.class)) {
            t = (T) Long.valueOf(s);
        }
    } catch (NumberFormatException e) {
        System.err.println(String.format("Cannot convert <%s> to type %s", s, type.getSimpleName()));
    }

    return t;
}

Answer 1

Rather than supplying a Class<T> , supply a Function<String, T> to convertCSVStringToList(more generally, it can be a Function<? super String, ? extends T> ), and remove your valueOf method:

public static <T> List<T> convertCSVStringToList(String s, Function<String, T> fn) {

Invoking this Function in the stream chain:

return Stream.of(s.split(","))
    .map(String::trim)
    .map(fn)
    .collect(Collectors.toList());

And invoke convertCSVStringToList like:

System.out.println(convertCSVStringToList(s, Integer::valueOf));

Answer 2

Instead of passing a class, which means you need to deal with each case individually in your valueOf method, you could pass a function that transforms the String to the desired object.

System.out.println(convertCSVStringToList(s, Integer::valueOf));

public static <T> List<T> convertCSVStringToList(String s, Function<String, T> transformer) {
  ...
    .map(String::trim)
    .map(transformer)
  ...
}