服务层定义自己的服务异常类

public class DownloadException extends RuntimeException {
    static final long serialVersionUID = 8598908007757442393L;

    public DownloadException() {
        super();
    }

    public DownloadException(String message) {
        super(message);
    }

    public DownloadException(String message, Throwable cause) {
        super(message, cause);
    }

    public DownloadException(Throwable cause) {
        super(cause);
    }

    public DownloadException(String message, Throwable cause,boolean enableSuppression,boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}