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How can emacs preview java jmod file like jar file from dired?

They are both zip file actually. I can preview jar file directly from dired, but not for jmod files.

I can view jar files like this after opening jar files from dired.

enter image description here

I tried adding jmod to dired-compress-file-suffixes, not working.

(add-to-list 'dired-compress-file-suffixes '("\\.jmod\\'" "" "unzip -o -d %o %i"))

by the way, jar is not in dired-compress-file-suffixes too.

Solution

  • Edit: After more discussion (see comments), we've established:

    • *.jmod files are a (slightly) different file format to *.jar files, in that the magic characters at the beginning are JM vs the PK used in jar files (and in zip files more generally).

    • Were it not for that, the suggested config changes below would actually be unnecessary, as the zip file detection in magic-fallback-mode-alist would handle them.

    • As it is, it's necessary to not only tell Emacs that these are archives, but additionally to modify the archive-find-type function to recognise what kind of archive they are, as this function currently only recognises the PK-based zip file format.

    For files starting with JM^C^D (as rendered by Emacs), the following change to archive-find-type should do the trick (but I don't know whether that's sufficient):

    @@ -772,6 +772,7 @@
   ;; as an archive by other software.
   (let (case-fold-search)
     (cond ((looking-at "\\(PK00\\)?[P]K\003\004") 'zip)
+          ((looking-at "JM\003\004") 'zip)
           ((looking-at "..-l[hz][0-9ds]-") 'lzh)
           ((looking-at "....................[\334]\247\304\375") 'zoo)
           ((and (looking-at "\C-z")     ; signature too simple, IMHO

    Original answer follows...

    The default auto-mode-alist contains the following entry for archive-mode, with a regexp that matches .jar files:

    ("\\.\\(arc\\|zip\\|lzh\\|lha\\|zoo\\|[jew]ar\\|xpi\\|rar\\|cbr\\|7z\\|squashfs\\|ARC\\|ZIP\\|LZH\\|LHA\\|ZOO\\|[JEW]AR\\|XPI\\|RAR\\|CBR\\|7Z\\|SQUASHFS\\)\\'"
 . archive-mode)

    The docstring for that variable also says:

    The extensions whose FUNCTION is `archive-mode' should also
appear in `auto-coding-alist' with `no-conversion' coding system.

    Hence this should do the trick:

    (add-to-list 'auto-mode-alist '("\\.jmod\\'" . archive-mode))
(add-to-list 'auto-coding-alist '("\\.jmod\\'" . no-conversion))