为什么NetBeans会说＆＃34;未报告的异常IOException;必须被抓住或宣布被抛出＆＃34;？

Question

这是我之前重复的问题Why is NetBeans saying "incompatible thrown types IOException in method reference"? [duplicate]的后续跟进。 为什么NetBeans在捕获IOException时告诉我"unreported exception IOException; must be caught or declared to be thrown"？

错误的屏幕截图

完整方法代码

/**
 * Either extracts or returns the pre-extracted language file for the given locale
 * 
 * @param locale the locale 
 * @return
 * @throws IOException 
 */
public static InputStream getLanguageFile(Locale locale) throws IOException
{
    File extracted = SaveConstants.inventSaveFileFor(Main.GAME_NAME, locale.toLanguageTag() + ".lang");
    if (!extracted.exists())
    {
        InputStream in = Resources.getLanguageStream(locale);
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        extracted.getParentFile().mkdirs();
        try
        {
            extracted.createNewFile();
            Writer writer = new FileWriter(extracted);
            reader
                .lines()
                .forEach((str) -> writer.write(str));
        }
        catch (IOException ex)
        {
            Logger.getLogger(Lang.class.getName()).log(Level.SEVERE, "Cannot extract language file for " + locale + ". Loading directly to map", ex);
            return in;
        }
    }
    else
        return new FileInputStream(extracted);
}

_{注意：我知道由于缺少回报而无法编译，但我希望在转到返回}

之前解决这个问题