Jlink - Assemble and Optimize a Set of Modules

Introducing jlink

jlink - assemble and optimize a set of modules, and their dependencies into a custom runtime image. This article gives a reference, for a tutorial on how to use it in practice, see here.

Synopsis

jlink [options] --module-path modulepath --add-modules module [, module...]

options Command-line options separated by spaces. See jlink Options.

modulepath The path where the jlink tool discovers observable modules. These modules can be modular JAR files, JMOD files, or exploded modules.

module The names of the modules to add to the runtime image. The jlink tool adds these modules and their transitive dependencies.

Description

The jlink tool links a set of modules, along with their transitive dependencies, to create a custom runtime image.

--add-modules mod[, mod...] Adds the named modules, mod, to the default set of root modules. The default set of root modules is empty.

--bind-services Link service provider modules and their dependencies.

-c={0|1|2} or --compress={0|1|2} Enable compression of resources:

0: No compression 1: Constant string sharing 2: ZIP --disable-plugin pluginname Disables the specified plug-in. See jlink Plug-ins for the list of supported plug-ins.

--endian {little|big} Specifies the byte order of the generated image. The default value is the format of your system's architecture.

-h or --help Prints the help message.

--ignore-signing-information Suppresses a fatal error when signed modular JARs are linked in the runtime image. The signature-related files of the signed modular JARs aren’t copied to the runtime image.

--launcher command=module or --launcher command=module/main Specifies the launcher command name for the module or the command name for the module and main class (the module, and the main class names are separated by a slash /).

--limit-modules mod[, mod...] Limits the universe of observable modules to those in the transitive closure of the named modules, mod, plus the main module, if any, plus any further modules specified in the --add-modules option.

--list-plugins Lists available plug-ins, which you can access through command-line options. See jlink Plug-ins.

-p or --module-path modulepath Specifies the module path.

If this option is not specified, then the default module path is $JAVA_HOME/jmods. This directory contains the java.base module and the other standard and JDK modules. If this option is specified but the java.base module cannot be resolved from it, then the jlink command appends $JAVA_HOME/jmods to the module path.

--no-header-files Excludes header files.

--no-man-pages Excludes man pages.

--output path Specifies the location of the generated runtime image.

--save-opts filename Saves jlink options in the specified file.

--suggest-providers [name, ...] Suggest providers that implement the given service types from the module path.

--version Prints version information.

@filename Reads options from the specified file.

An options file is a text file that contains the options and values that you would typically 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 jlink command:

#Wed Dec 07 00:40:19 EST 2016
--module-path mlib
--add-modules com.greetings
--output greetingsapp

Options

For plug-in options that require a pattern-list, the value is a comma-separated list of elements, with each element using one the following forms:

• glob-pattern
• glob:glob-pattern
• regex:regex-pattern
• @filename
  • filename is the name of a file that contains patterns to be used, one pattern per line.

Plugins

For a complete list of all available plug-ins, run the command jlink --list-plugins.

compress Options:

--compress={0|1|2}[:filter=pattern-list]

Description:

Compresses all resources in the output image.

Level 0: No compression
Level 1: Constant string sharing
Level 2: ZIP
An optional pattern-list filter can be specified to list the pattern of files to include.

include-locales Options:

--include-locales=langtag[,langtag]*

Description:

Includes the list of locales where langtag is a BCP 47 language tag.
This option supports locale matching as defined in RFC 4647.
Ensure that you add the module jdk.localedata when using this option.

Example:

--add-modules jdk.localedata --include-locales=en,ja,*-IN

order-resources

Options:

--order-resources=pattern-list

Description:

Orders the specified paths in priority order.
If @filename is specified, then each line in pattern-list must be an exact match for
the paths to be ordered.

Example:

--order-resources=/module-info.class,@classlist,/java.base/java/lang/

strip-debug

Options:

--strip-debug

Description:

Strips debug information from the output image.

Examples

The following command creates a runtime image in the directory greetingsapp. This command links the module com.greetings, whose module definition is contained in the directory mlib.

jlink --module-path mlib --add-modules com.greetings --output greetingsapp

The following command lists the modules in the runtime image greetingsapp:

greetingsapp/bin/java --list-modules
com.greetings
java.base@11
java.logging@11
org.astro@1.0

The following command creates a runtime image in the directory compressedrt that’s stripped of debug symbols, uses compression to reduce space, and includes French language locale information:

jlink --add-modules jdk.localedata --strip-debug --compress=2 --include-locales=fr --output compressedrt

The following example compares the size of the runtime image compressedrt with fr_rt, which isn’t stripped of debug symbols and doesn’t use compression:

jlink --add-modules jdk.localedata --include-locales=fr --output fr_rt

du -sh ./compressedrt ./fr_rt
23M     ./compressedrt
36M     ./fr_rt

The following example lists the providers that implement java.security.Provider:

jlink --suggest-providers java.security.Provider

Suggested providers:
  java.naming provides java.security.Provider used by java.base
  java.security.jgss provides java.security.Provider used by java.base
  java.security.sasl provides java.security.Provider used by java.base
  java.smartcardio provides java.security.Provider used by java.base
  java.xml.crypto provides java.security.Provider used by java.base
  jdk.crypto.cryptoki provides java.security.Provider used by java.base
  jdk.crypto.ec provides java.security.Provider used by java.base
  jdk.crypto.mscapi provides java.security.Provider used by java.base
  jdk.security.jgss provides java.security.Provider used by java.base

The following example creates a custom runtime image named mybuild that includes only java.naming and jdk.crypto.cryptoki and their dependencies but no other providers. Note that these dependencies must exist in the module path:

jlink --add-modules java.naming,jdk.crypto.cryptoki --output mybuild

The following command is similar to the one that creates a runtime image named greetingsapp, except that it will link the modules resolved from root modules with service binding:

jlink --module-path mlib --add-modules com.greetings --output greetingsapp --bind-services

The following command lists the modules in the runtime image greetingsapp created by this command:

greetingsapp/bin/java --list-modules
com.greetings
java.base@11
java.compiler@11
java.datatransfer@11
java.desktop@11
java.logging@11
java.management@11
java.management.rmi@11
java.naming@11
java.prefs@11
java.rmi@11
java.security.jgss@11
java.security.sasl@11
java.smartcardio@11
java.xml@11
java.xml.crypto@11
jdk.accessibility@11
jdk.charsets@11
jdk.compiler@11
jdk.crypto.cryptoki@11
jdk.crypto.ec@11
jdk.crypto.mscapi@11
jdk.internal.opt@11
jdk.jartool@11
jdk.javadoc@11
jdk.jdeps@11
jdk.jfr@11
jdk.jlink@11
jdk.localedata@11
jdk.management@11
jdk.management.jfr@11
jdk.naming.dns@11
jdk.naming.rmi@11
jdk.security.auth@11
jdk.security.jgss@11
jdk.zipfs@11
org.astro@1.0

More Learning