java - 为枚举实现 MessageBodyReader

Question

我正在尝试实现一个新的 MessageBodyReader/Writer 组合，但阅读器部分遇到问题。鉴于以下声明

public class Jsr367EnumProvider<T extends Enum> implements
                                                MessageBodyReader<T>,
                                                MessageBodyWriter<T>

可以工作，但有一条警告说 Enum是生的。因此，为了修复它，我尝试输入 Enum<?>

但是这会在我的 readFrom 中产生错误方法

@Override
public T readFrom(final Class<T> type,
    final Type genericType,
    final Annotation[] annotations,
    final MediaType mediaType,
    final MultivaluedMap<String, String> httpHeaders,
    final InputStream inputStream) throws IOException,
        WebApplicationException {

    // TODO support other encodings using the HTTP Header
    try (Scanner s = new Scanner(inputStream).useDelimiter("\\A")) {
        return (T) Enum.valueOf(type, s.next());
    }

}

这也警告了未经检查的 Actor 。有没有办法解决这个问题而不诉诸 @SupressWarnings ？

Answer 1

不，没有。回想一下您尝试转换的方法的签名:

Enum.valueOf(Class<T> enumType, String name)

严格来说，您提供的代码，您无法摆脱警告。因此，抑制它，但遵循良好的做法，例如《Effective Java 2nd Edition: Item 24: Eliminate unchecked warnings:》中所规定的内容:

• Eliminate every unchecked warning that you can.
• If you can't eliminate a warning, and you can prove that the code that provoked the warning is typesafe, then (and only then) suppress the warning with @SuppressWarning("unchecked") annotation.
• Always use the SuppressWarning annotation on the smallest scope possible.
• Every time you use an @SuppressWarning("unchecked") annotation, add a comment saying why it's safe to do so.