上面的代码应该很容易直接移植到ImageIO。
我尽可能地保留了变量名，使其更容易理解，并重写为使用try-with-resources。我相信这应该可以工作：

private File createJPEG(String tifFilePath) {
    try (ImageInputStream s = ImageIO.createImageInputStream(new File(tifFilePath))) {
        Iterator<ImageReader> readers = ImageIO.getImageReadersByFormatName("TIFF"); // Could also use ImageIO.getImageReaders(s) to support any input format
        if (!readers.hasNext()) {
            return null; // ...or throw new IllegalArgumentException or similar
        }

        ImageReader dec = readers.next();
        dec.setInput(s);

        // The above code doesn't seem to use param, but if needed that is also possible
        ImageReadParam param = null; // dec.getDefaultReadParam() or new TIFFImageReadParam()
        RenderedImage op = dec.readAsRenderedImage(0, param); // Could als use dec.read(0, param) in most cases 
        
        File jpgFile = new File(tifFilePath.replace("tif", "jpg"));

        try (ImageOutputStream fos = ImageIO.createImageOutputStream(jpgFile)) {
            JPEGImageWriteParam jpgparam = new JPEGImageWriteParam(Locale.getDefault());
            jpgparam.setCompressionMode(MODE_EXPLICIT);
            jpgparam.setCompressionQuality(0.67f); // You might want to tune this parameter to get same quality/compression ratio as JAI

            ImageWriter en = ImageIO.getImageWritersByFormatName("JPEG").next();
            en.setOutput(fos);
            en.write(null, new IIOImage(op, null, null), jpgparam);
        }
    } catch (IOException ex) {
        LOGGER.error(ex);
    }

    return null; // What the original code does, probably you want to return jpgFile?
}