Running a JAR file without directly calling `java`

Question

I am deploying a command-line tool that is written in Java that accepts command-line arguments. I have it packaged as a JAR file because it is convenient to have a single file.

The problem is that to run it you must first call java -jar (filename) (args) and that is quite annoying.

The current way I have it is to have a simple bash script that launches it, but this is less than ideal.

Is there anyway (in Linux, Ubuntu Server) to make a JAR file that invokes the Java VM by itself? I've looked for a shebang, but couldn't find one (which of course makes sense since it is compiled code).

This is what I want to do: myprogram.jar arg1 -arg2 instead of this: java -jar myprogram.jar arg1 -arg2

Thanks,
Brian

Answer 1

On linux it is not possible.

The common way is to have a shell script that looks (roughly) like this:

#!/bin/sh
java -jar myprogram.jar $*

In windows you can set that double clicking a jar file will be bound to java -jar %1 which effectively makes it an executable from the user's perspective.

Answer 2

See Documentation/java.txt in the Linux Kernel documentation, which tells you how to configure a system using the binfmt_misc kernel module to run Jar files automatically. However, this is a configuration option you change on a computer, not something you change about the jar file, so it doesn't follow the jar file from system to system.

Answer 3

The .zip file format (upon which the .jar format is based) seems to be robust in the presence of extra data prepended to the file. Thus if you use the cat command to put a shebang before the zip data in the jar file, and make the file executable, then you can call the jar file like you would call any ordinary shell script.

For example: (Note that the unzip -l command is just to illustrate the point. It doesn't change anything about the .jar and can be omitted when you're actually doing this process.)

[bloom@cat-in-the-hat ~]$ java -jar tex4ht.jar 
   xtpipes (2009-01-27-22:19)
   Command line options: 
     java xtpipes [-trace] [-help] [-m] [-E] [-s script_file] [-S script_map]
                  [-i script_dir] [-o out_file] 
                  [-x...ml2xml_arg...]  (-d in_data | in_file)
     -m        messages printing mode
     -E        error messages into exception calls
     in_data   XML data directly into the command line

[bloom@cat-in-the-hat ~]$ cat header.txt 
#!/usr/bin/java -jar
[bloom@cat-in-the-hat ~]$ cat header.txt tex4ht.jar > tex4ht_exe.jar 
[bloom@cat-in-the-hat ~]$ unzip -l tex4ht_exe.jar
Archive:  tex4ht_exe.jar
warning [tex4ht_exe.jar]:  21 extra bytes at beginning or within zipfile
  (attempting to process anyway)
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2009-07-09 15:48   META-INF/
       42  2009-07-09 15:47   META-INF/MANIFEST.MF
        0  2009-07-09 15:48   ./
        0  2009-07-09 15:48   tex4ht/
     2217  2009-07-09 15:48   tex4ht/DbUtilities.class
     2086  2009-07-09 15:48   tex4ht/GroupMn.class
     6064  2009-07-09 15:48   tex4ht/HtJsml.class
     4176  2009-07-09 15:48   tex4ht/HtSpk.class
     1551  2009-07-09 15:48   tex4ht/JsmlFilter.class
     2001  2009-07-09 15:48   tex4ht/JsmlMathBreak.class
     6172  2009-07-09 15:48   tex4ht/OoFilter.class
     3449  2009-07-09 15:48   tex4ht/OoUtilities.class
     1468  2009-07-09 15:48   tex4ht/OomFilter.class
      346  2009-07-09 15:48   xtpipes.class
        0  2009-07-09 15:48   xtpipes/
     4071  2009-07-09 15:48   xtpipes/FileInfo.class
     6904  2009-07-09 15:48   xtpipes/InputObject.class
    25906  2009-07-09 15:48   xtpipes/Xtpipes.class
     1238  2009-07-09 15:48   xtpipes/Xtpipes$5.class
      713  2009-07-09 15:48   xtpipes/Xtpipes$3.class
     1533  2009-07-09 15:48   xtpipes/Xtpipes$1.class
      709  2009-07-09 15:48   xtpipes/Xtpipes$7.class
     1294  2009-07-09 15:48   xtpipes/XtpipesEntityResolver.class
     1235  2009-07-09 15:48   xtpipes/Xtpipes$6.class
     3367  2009-07-09 15:48   xtpipes/Xtpipes$4.class
      709  2009-07-09 15:48   xtpipes/Xtpipes$8.class
     1136  2009-07-09 15:48   xtpipes/Xtpipes$2.class
      875  2009-07-09 15:48   xtpipes/XtpipesPrintWriter.class
     1562  2009-07-09 15:48   xtpipes/XtpipesUni.class
        0  2009-07-09 15:48   xtpipes/util/
     5720  2009-07-09 15:48   xtpipes/util/ScriptsManager.class
     1377  2009-07-09 15:48   xtpipes/util/ScriptsManagerLH.class
---------                     -------
    87921                     32 files
[bloom@cat-in-the-hat ~]$ chmod +x tex4ht_exe.jar
[bloom@cat-in-the-hat ~]$ ./tex4ht_exe.jar 
   xtpipes (2009-01-27-22:19)
   Command line options: 
     java xtpipes [-trace] [-help] [-m] [-E] [-s script_file] [-S script_map]
                  [-i script_dir] [-o out_file] 
                  [-x...ml2xml_arg...]  (-d in_data | in_file)
     -m        messages printing mode
     -E        error messages into exception calls
     in_data   XML data directly into the command line