import com.sun.xml.internal.ws.encoding.HasEncoding; //导入依赖的package包/类
/**
 * Gives the encoding with which XMLStreamWriter is created.
 *
 * @param writer XMLStreamWriter for which encoding is required
 * @return null if cannot be found, else the encoding
 */
public static @Nullable String getEncoding(XMLStreamWriter writer) {
    /*
     * TODO Add reflection logic to handle woodstox writer
     * as it implements XMLStreamWriter2#getEncoding()
     * It's not that important since woodstox writer is typically wrapped
     * in a writer with HasEncoding
     */
    return (writer instanceof HasEncoding)
            ? ((HasEncoding)writer).getEncoding()
            : null;
}