JMOD(1)

📦 version 17.0.21.0.3.u1, in arch rolling

✨ NAME ✨

okay bestie, welcome to jmod(1) from the JDK Commands lineup 💅 this page is literally about the jmod tool — it creates JMOD files and lists the content of existing JMOD files. (It also extracts, describes, and hashes, but we’ll get there, don’t rush her.)

🦋 SYNOPSIS 🦋

jmod (create|extract|list|describe|hash) [options] jmod-file

Includes the following:

🌸 Main operation modes

  • create — creates a new JMOD archive file.
  • extract — extracts all the files from the JMOD archive file.
  • list — prints the names of all the entries.
  • describe — prints the module details.
  • hash — determines leaf modules and records the hashes of the dependencies that directly and indirectly require them.

🎀 Options

  • options — see Options for jmod.

🫶 Required

  • jmod-file — specifies the name of the JMOD file to create or from which to retrieve information.

🌈 DESCRIPTION 🌈

Note: for most development tasks — including deploying modules on the module path or publishing them to a Maven repository — keep packaging modules in modular JAR files. The jmod tool is intended for modules that have native libraries or other configuration files, or for modules that you intend to link, with the jlink tool, to a runtime image.

The JMOD file format lets you aggregate files other than .class files, metadata, and resources. This format is transportable but not executable, which means you can use it during compile time or link time but not at run time. bestie, it’s giving “backstage pass, not main-character-at-runtime energy” 💀

Many jmod options involve specifying a path whose contents are copied into the resulting JMOD files. These options copy all the contents of the specified path, including subdirectories and their contents, but exclude files whose names match the pattern specified by the --exclude option.

With the --hash-modules option or the jmod hash command, you can, in each module’s descriptor, record hashes of the content of the modules that are allowed to depend upon it, thus “tying” together these modules 🔗 This enables a package to be exported to one or more specifically-named modules and to no others through qualified exports. The runtime verifies if the recorded hash of a module matches the one resolved at run time; if not, the runtime returns an error. no cap, that vibe check is strict.

💖 OPTIONS FOR JMOD 💖

  • --class-path path — specifies the location of application JAR files or a directory containing classes to copy into the resulting JMOD file.
  • --cmds path — specifies the location of native commands to copy into the resulting JMOD file.
  • --config path — specifies the location of user-editable configuration files to copy into the resulting JMOD file.
  • --dir path — specifies the location where jmod puts extracted files from the specified JMOD archive.
  • --dry-run — performs a dry run of hash mode. It identifies leaf modules and their required modules without recording any hash values.
  • --exclude pattern-list — excludes files matching the supplied comma-separated pattern list, each element using one of the following forms:
    • glob-pattern
    • glob:glob-pattern
    • regex:regex-pattern

See the FileSystem.getPathMatcher method for the syntax of glob-pattern. See the Pattern class for the syntax of regex-pattern, which represents a regular expression.

  • --hash-modules regex-pattern — determines the leaf modules and records the hashes of the dependencies directly and indirectly requiring them, based on the module graph of the modules matching the given regex-pattern. The hashes are recorded in the JMOD archive file being created, or a JMOD archive or modular JAR on the module path specified by the jmod hash command.
  • --header-files path — specifies the location of header files to copy into the resulting JMOD file.
  • --help or -h — prints a usage message.
  • --help-extra — prints help for extra options.
  • --legal-notices path — specifies the location of legal notices to copy into the resulting JMOD file.
  • --libs path — specifies location of native libraries to copy into the resulting JMOD file.
  • --main-class class-name — specifies main class to record in the module-info.class file.
  • --man-pages path — specifies the location of man pages to copy into the resulting JMOD file.
  • --module-version module-version — specifies the module version to record in the module-info.class file.
  • --module-path path or -p path — specifies the module path. This option is required if you also specify --hash-modules.
  • --target-platform platform — specifies the target platform.
  • --version — prints version information of the jmod tool.
  • @filename — reads options from the specified file.

An options file is a text file that contains the options and values that you would ordinarily enter in a command prompt. Options may appear on one line or on several lines. You may not specify environment variables for path names. You may comment out lines by prefixing a hash symbol (#) to the beginning of the line.

The following is an example of an options file for the jmod command:

#Wed Dec 07 00:40:19 EST 2016
create --class-path mods/com.greetings --module-path mlib
  --cmds commands --config configfiles --header-files src/h
  --libs lib --main-class com.greetings.Main
  --man-pages man --module-version 1.0
  --os-arch "x86_x64" --os-name "Mac OS X"
  --os-version "10.10.5" greetingsmod

🌟 EXTRA OPTIONS FOR JMOD 🌟

In addition to the options described in Options for jmod, the following are extra options that can be used with the command.

  • --do-not-resolve-by-default — exclude from the default root set of modules.
  • --warn-if-resolved — hint for a tool to issue a warning if the module is resolved. One of deprecated, deprecated-for-removal, or incubating.

🍓 JMOD CREATE EXAMPLE 🍓

The following is an example of creating a JMOD file:

jmod create --class-path mods/com.greetings --cmds commands
  --config configfiles --header-files src/h --libs lib
  --main-class com.greetings.Main --man-pages man --module-version 1.0
  --os-arch "x86_x64" --os-name "Mac OS X"
  --os-version "10.10.5" greetingsmod

🔥 JMOD HASH EXAMPLE 🔥

The following example demonstrates what happens when you try to link a leaf module (in this example, ma) with a required module (mb), and the hash value recorded in the required module doesn’t match that of the leaf module. it’s giving drama, but make it cryptographic 💀

  1. Create and compile the following .java files:
    • jmodhashex/src/ma/module-info.java
module ma {
  requires mb;
}
  • jmodhashex/src/mb/module-info.java
module mb {
}
  • jmodhashex2/src/ma/module-info.java
module ma {
  requires mb;
}
  • jmodhashex2/src/mb/module-info.java
module mb {
}
  1. Create a JMOD archive for each module. Create the directories jmodhashex/jmods and jmodhashex2/jmods, and then run the following commands from the jmodhashex directory, then from the jmodhashex2 directory:
    • jmod create --class-path mods/ma jmods/ma.jmod
    • jmod create --class-path mods/mb jmods/mb.jmod
  2. Optionally preview the jmod hash command. Run the following command from the jmodhashex directory:
jmod hash --dry-run -module-path jmods --hash-modules .*

The command prints the following:

Dry run:
mb
  hashes ma SHA-256 07667d5032004b37b42ec2bb81b46df380cf29e66962a16481ace2e71e74073a

This indicates that the jmod hash command (without the --dry-run option) will record the hash value of the leaf module ma in the module mb.

  1. Record hash values in the JMOD archive files contained in the jmodhashex directory. Run the following command from the jmodhashex directory:
jmod hash --module-path jmods --hash-modules .*

The command prints the following:

Hashes are recorded in module mb
  1. Print information about each JMOD archive contained in the jmodhashex directory. Run the highlighted commands from the jmodhashex directory:
jmod describe jmods/ma.jmod
ma
  requires mandated java.base
  requires mb
jmod describe jmods/mb.jmod
mb
  requires mandated java.base
  hashes ma SHA-256 07667d5032004b37b42ec2bb81b46df380cf29e66962a16481ace2e71e74073a
  1. Attempt to create a runtime image that contains the module ma from the directory jmodhashex2 but the module mb from the directory jmodhashex. Run the following command from the jmodhashex2 directory:
    • Linux and OS X:
jlink --module-path $JAVA_HOME/jmods:jmods/ma.jmod:../jmodhashex/jmods/mb.jmod --add-modules ma --output ma-app
  • Windows:
jlink --module-path %JAVA_HOME%/jmods;jmods/ma.jmod;../jmodhashex/jmods/mb.jmod --add-modules ma --output ma-app

The command prints an error message similar to the following:

Error: Hash of ma (a2d77889b0cb067df02a3abc39b01ac1151966157a68dc4241562c60499150d2) differs to
expected hash (07667d5032004b37b42ec2bb81b46df380cf29e66962a16481ace2e71e74073a) recorded in mb

mwah 💋 this iconic little page is from JDK 17, dated 2021, and its manual-page tag is JMOD(1). periodt.

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