Want to learn, explore or use Java instantly without setup ?
Do you like Java but use python, groovy, kotlin or similar languages for your scripts ?
Ever tried out Java 10+ support for running .java files directly in your shell but felt it was a bit too cumbersome ?
Then try jbang which lets you do this:
$ jbang --init=cli hello.java
$ jbang hello.java Max!
[jbang] Resolving dependencies...
[jbang] Resolving info.picocli:picocli:4.2.0...Done
[jbang] Dependencies resolved
[jbang] Building jar...
Hello Max!
$ jbang hello.java -h
Usage: hello [-hV] <greeting>
hello made with jbang
<greeting> The greeting to print
-h, --help Show this help message and exit.
-V, --version Print version information and exit.Instant cli app generated built using java and picocli as a dependency that was fetched as needed for the compilation and execution.
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.javaScripting for Java 8 and upwards -
.jshvia JShell from Java 9 and upwards -
Works on [windows] Windows, [apple] OSX and [linux] Linux
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Install using SDKMan ([apple]/[linux]), Homebrew ([apple]), Chocolatey ([windows]) or Scoop ([windows])
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Dependency declarations using
//DEPS <gav>for automatic dependency resolution -
Control compile and runtime options with
//JAVAC_OPTIONS <flags>and//JAVA_OPTIONS <flags> -
Compiled jar and Dependency resolution caching
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(EXPERIMENTAL) native-image generation (
--native) -
Launch with debug enabled for instant debugging from your favorite IDE
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Transparent launch of JavaFX Applications on Java 8 and higher.
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Can be used for writing plugins to other cli’s like
kubectl -
Init templates to get started easily (
jbang --init=cli hello.java) -
Generate gradle and IDE config with dependencies for easy editing in your favorite IDE (
jbang --edit myfile.java) -
(PLANNED) Lookup dependencies with a short-hand name, i.e.
// DEPS log4j:1.2+,picoclifor quick getting started.
To use it simply install jbang and run jbang yourscript.java
Minimum Java 8, Recommended: Java 11+
Tested and verified to use on OSX, Linux and Windows.
To use jbang Java 8 is the minimum required version, however Java 11 or higher is recommended.
To install both java and jbang we recommend sdkman on Linux and OSX.
curl -s "https://get.sdkman.io" | bash # (1)
source ~/.bash_profile # (2)
sdk install java # (3)Once Java is installed and ready, you install jbang with
sdk install jbangTo test your installation run:
jbang --helpThis should print out usage information.
To update run:
sdk update jbangOn Windows you can install both java and jbang` with Chocolatey.
From a command prompt with enough rights to install with choco:
choco install jdk11
Once Java in installed run:
choco install jbang
To upgrade to latest version:
choco upgrade jbang
The latest package will be published to jbang choco package page, it might be a bit delayed as the review is still manual. In case the default version is not the latest you can see the version list and install specific version using:
choco install jbang --version=<version number>
On Windows you can also install jbang` with Scoop.
scoop bucket add jbangdev https://github.com/jbangdev/scoop-bucket
scoop install jbangTo upgrade to latest version:
scoop update jbang
On OSX you can install 'java' and jbang with Homebrew using custom taps.
To install Java 11:
brew tap AdoptOpenJDK/openjdk
brew cask install adoptopenjdk11Once Java is installed you can use brew with jbangdev/tap to get jbang:
brew install jbangdev/tap/jbang
To upgrade to latest version:
brew upgrade jbangdev/tap/jbang
If you encounter an issue in jbang that is not present in an older version,
you can revert back to that older version following these steps:
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Find the commit id for the version to revert to (e.g.
0.8.1).$ cd "$(brew --repo jbangdev/tap)" $ git log master -- Formula/jbang.rb ... commit fd70f1bc0a7f69d81cfb5b08a0d2bb698fbd01b2 Author: Max Rydahl Andersen <[email protected]> Date: Tue Jan 21 00:33:05 2020 +0000 jbang v0.8.1 -
Checkout the the version.
$ git checkout fd70f1bc0a7f69d81cfb5b08a0d2bb698fbd01b
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Unlink current
jbangversion.$ brew unlink jbang Unlinking /usr/local/Cellar/jbang/0.13.2... 1 symlinks removed
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Install the older version.
$ HOMEBREW_NO_AUTO_UPDATE=1 brew install jbang ... 🍺 /usr/local/Cellar/jbang/0.8.1: 18 files, 2.9MB, built in 6 seconds -
Verify the version.
$ jbang --version 0.8.1
INFO: These builds are not fully automated yet thus might be slightly behind.
You can install rpm packages from Fedora Copr by doing the following:
dnf copr enable maxandersen/jbang
dnf install jbangThe COPR currently includes builds from various versions of CentOS, Fedora, Mageia and OpenSuse.
You can run jbang via Docker:
docker run -v `pwd`:/ws --workdir=/ws jbangdev/jbang-action helloworld.javaor if you prefer using Quay.io:
docker run -v `pwd`:/ws --workdir=/ws quay.io/jbangdev/jbang-action helloworld.javaThe same container images can be used with GitHub Actions, see jbang-action for details.
Unzip the latest binary release, put the jbang-<version>/bin folder in to your $PATH and you are set.
A script is just a single .java file with a classic static main method or a .jsh file which will be passed to jshell.
Below is an (almost) minimal example you can save in helloworld.java or simply run jbang --init hellworld.java:
//usr/bin/env jbang "$0" "$@" ; exit $? // (1)
class helloworld { // (2)
public static void main(String[] args) {
if(args.length==0) {
System.out.println("Hello World!");
} else {
System.out.println("Hello " + args[0]);
}
}
}-
By using this
//style instead of shebang#!you trickbash,zshetc. to run this as a script while still being valid java code. -
A classname, can be anything when using
jbangbut to be valid java for most IDEs you’ll want to name it the same as the source file.
Now to run this you can call it via jbang:
jbang helloworld.javaor if on Linux/OSX run it directly. If you created it manually you need to mark it as executable before running it.
chmod +x helloworld.java
./helloworld jbang!You can use http(s):/ and file:/ url’s for input:.
jbang https://github.com/jbangdev/jbang/blob/master/examples/helloworld.javaFor safety reasons jbang will not run arbitrary urls before you indicated you trust their source. Thus when running the above for the first time you will see the following warning about the url not being a trusted source:
[jbang] https://github.com/jbangdev/jbang/blob/master/examples/helloworld.java is not from a trusted source thus aborting.
If you trust the url to be safe to run are here a few suggestions:
Limited trust:
jbang --trust=https://github.com/jbangdev/jbang/
Trust all subdomains:
jbang --trust=*.github.com
Trust all sources (WARNING! disables url protection):
jbang --trust="*"
For more control edit ~/.jbang/trusted-sources.json
[jbang] Run with --verbose for more detailsTo enable running it you need to mark that url or a sub part of it as a trusted source.
i.e. jbang --trust=https://github.com/jbangdev/jbang/ will tell jbang to trust anything with that base url.
You can see more in the comments of the ~/.jbang/trusted-sources.json.
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Sites such as github, gitlab, bitbucket, gist, twitter and carbon.now.sh jbang will try and extract the proper source rather than the raw html.
i.e. doing |
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URL’s will follow redirects. In case you need to use it with sites with self-signed/non-trusted certificates you can
if you trust the site use |
There are support for using native-image from GraalVM project to produce a binary executable.
Since not all java libraries can automatically be built with native-image - especially if using reflection feature are considered highly experimental.
Just run jbang --native helloworld.java and jbang will use native-image from either JAVA_HOME/bin or GRAALVM_HPME/bin to
produce a native image binary.
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If you use |
There are support to run .jsh via jshell. The advantage of jshell is that you do not need to have a class or static main method.
Classic jshell does not support passing in arguments nor system properties, jbang does.
In the case of .jsh files jbang injects a startup script that declares a String[] args which will contain any passed in arguments,
and it sets any properties passed in with -Dkey=value as parameter to jbang.
Example:
System.out.println("Hello " + (args.length>0?args[0]:"World")); // (1)
System.setProperty("key", "value"); // (2)-
Line where
argsare accessible without previous declaration. -
System properties set when passed as
-Darguments tojbang
If you use `--interactive` `jbang` will let `jshell` enter into interactive/REPL mode. You write `/exit` to leave this mode.
To get started you can run jbang --init helloworld.java and a simple java class with a static main is generated.
Using jbang --init=cli helloworld.java you get a more complete Hello World CLI using picocli as dependencies.
If you want to write real scripts you will want to use some java libraries.
To specify dependencies you use gradle-style locators or links to Git sources. Below are examples for log4j.
//usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS log4j:log4j:1.2.17 (1)
import static java.lang.System.out;
import org.apache.log4j.Logger;
import org.apache.log4j.BasicConfigurator;
import java.util.Arrays;
class classpath_example {
static final Logger logger = Logger.getLogger(classpath_example.class);
public static void main(String[] args) {
BasicConfigurator.configure(); // (2)
logger.info("Welcome to jbang");
Arrays.asList(args).forEach(arg -> logger.warn("arg: " + arg));
logger.info("Hello from Java!");
}
}-
//DEPS has to be start of line and can be one or more space separated dependencies.
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Minimal logging setup - required by log4j.
Now when you run this the first time with no existing dependencies installed you should get an output like this:
$ ./classpath_example.java
[jbang] Resolving dependencies...
[jbang] Resolving log4j:log4j:1.2.17...Done
[jbang] Dependencies resolved
0 [main] INFO classpath_example - Welcome to jbang
1 [main] INFO classpath_example - Hello from Java!Instead of gradle-style locators you can also use URLs to projects on GitHub, GitLab or BitBucket. Links to those projects will then be converted to references to artifacts on jitpack. You can use links to the root of the project, to the root of a tag/release and to specific commits.
If the project you link to has multiple modules and you want only a specific module you can specify the
name of the module by appending #name-of-module to the URL.
And finally if the link you provide is to a specific branch of the project then you need to append
#:SNAPSHOT to the URL. (If you have both a branch and a module name then use #name-of-module:SNAPSHOT)
Examples of links and their resulting locator:
Link |
Locator |
com.github.jbangdev:jbang:master-SNAPSHOT |
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com.github.jbangdev:jbang:v1.2.3 |
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com.github.jbangdev:jbang:f1f34b031d |
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com.github.jbangdev.jbang:mymodule:master-SNAPSHOT |
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com.github.jbangdev:jbang:mybranch-SNAPSHOT |
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https://github.com/jbangdev/jbang/tree/mybranch#mymodule:SNAPSHOT |
com.github.jbangdev.jbang.mymodule:mybranch-SNAPSHOT |
In case you prefer jbang to just fail-fast when dependencies cannot be found locally you can run jbang in offline mode using
jbang -o or jbang --offline. In this mode jbang will simply fail if dependencies have not already been cached already.
By default jbang uses jcenter as its repository as it is a superset of Maven Central
and supposedly should be faster.
And if you are using the above mentioned URL dependencies jitpack will be added automatically as well.
If that is not sufficient for you or need some custom repo you can use //REPOS id=repourl to
state which repository URL to use.
For ease of use there are also a few shorthands to use popular commonly available repositories.
Short name |
Description |
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Maven Central |
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Following example enables use of Maven Central and add a custom acme repository.
//REPOS mavenCentral,acme=https://maven.acme.local/maven|
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If you add any |
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For secure authentication |
There is also support for using Groovy lang style @Grab syntax.
//usr/bin/env jbang "$0" "$@" ; exit $?
import static java.lang.System.out;
import org.apache.log4j.Logger;
import org.apache.log4j.BasicConfigurator;
import java.util.Arrays;
import groovy.lang.Grab; // (1)
import groovy.lang.Grapes;
import groovy.lang.GrabResolver;
@GrabResolver("mavenCentral") // (2)
@GrabResolver(name='acme', root='https://maven.acme.local/maven')
@Grapes({ // (3)
@Grab(group="org.codehaus.groovy", module="groovy", version="2.5.8"), // (4)
@Grab(module = "log4j", group = "log4j", version = "1.2.17")
})
class classpath_example {
static final Logger logger = Logger.getLogger(classpath_example.class);
public static void main(String[] args) {
BasicConfigurator.configure();
Arrays.asList(args).forEach(arg -> out.println(arg));
}
}-
Import needed to make the compiler be okey with
@Grabannotation. -
Using
GrabResolverto enablemavenCentraland customacmerepository -
In Groovy you normally put
@Grabon import statements. That is not allowed in Java thus when having multiple imports you need to put them in a@Grapesannotation first. -
jbangwill grab any@Grabannotation and assume it is declaring dependencies.
In dependencies you can refer to environment and system properties to parameterize the dependencies.
It uses the format ${[env.]propertyname:<defaultvalue>}.
Furthermore to align with properties commonly used to make dependency resolution portable
jbang exposes properties similar to what the os-maven-plugin does.
Plus for ease of use for javafx dependencies it also setup a property named ${os.detected.jfxname}.
Examples:
${env.USER} = 'max'
${os.name} = 'Mac OS X'
${non.existing.key:empty} = 'empty'
${os.detected.jfxname} = 'mac'This can be put to use in //DEPS like so:
//DEPS org.openjfx:javafx-graphics:11.0.2:${os.detected.jfxname}Here we use the properties to avoid hardcoding your script to a specific operating system.
If jbang detects you have a javafx- dependency in your list of dependencies
it will if you java command supports Java modules automatically set the necessary
--module-path and --add-modules.
See examples/jfx.java and examples/jfxtiles.java for examples of this.
You can use jbang to write plugins for cli’s like kubectl, git, etc.
They expect their plugins to be named like <cmd>-<plugin>, i.e. kubectl-myplugin.
Furthermore some of them, particularly kubectl currently require the file to start with #! otherwise you get a excc format error.
jbang has a bit of auto-magic to help in both cases.
jbang lets you name your file without a .java or .jsh extension, such
as kubectl-myplugin. jbang will in this case copy the file to a temporary
directory using kebab-case to map the name to a proper java class name.
i.e. If you make a file called kubectl-myplugin then jbang will assume the actual class name to launch
will be KubectlMyPlugin.
Note, similar is done when using --edit, here the symbolic link will be made so the IDE will treat it as
regular camel cased java class.
Note: If you do not follow this naming pattern you will get a compile error as javac expect the public class name are equal to the filename.
For extension less scripts, you can put #!' header in beginning to let apps recognize
it is to be treated as a script. To avoid issues when compiling `jbang will remove
that line before compiling.
For now this is required for kubectl plugin but not git. Issue opened on this limitation.
You can edit your script in your IDE by using jbang --edit helloworld.java. This will generate a project in a temporary location with symbolic links to your script
and output the generated folder name. The easiest way to use that is to use it in a call to your IDE:
code `jbang --edit helloworld.java`If you add additional dependencies to your file just re-run the edit command and the relevant files will be regenerated with the updated dependencies.
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On Windows you might need elevated privileges to create symbolic links. If you don’t have permissions then
the --edit option will result in an error. To use it enable symbolic links for your user or run your shell/terminal as administrator
to have this feature working.
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You can also use --edit-live[=editor] and jbang will launch your editor while watching
for file changes and regenerate the temporary project to pick up changes in dependencies.
The editor used will be what is specified as argument to --edit-live or default to $JBANG_EDITOR, $VISUAL or $EDITOR in that order.
The --edit feature been tested with the following IDE’s:
jbang
The --edit feature works with various IDE’s - it generates a build.gradle to use with IDE’s that understands Gradle directly.
For speed and consistency jbang also generates IDE specific settings.
Currently launchers and project files are generated for Eclipse and vscode. Intellij just reads build.gradle for now thus
to run/debug you will need to manually set it up.
When running .java scripts with jbang you can pass the --debug-flag and the script will enable debug,
suspend the execution and wait until you connect a debugger to port 4004.
jbang --debug helloworld.java
Listening for transport dt_socket at address: 4004You can change the debug port by passing in a number to the debug argument, i.e. --debug=4321.
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Be sure to put a breakpoint in your IDE/debugger before you connect to make the debugger actually stop when you need it. |
If you want to tweak memory settings or enable preview features you can setup the necessary options using
//JAVA_OPTS and //COMPILER_OPTS as in the following example using Java 14 experimental record feature:
//usr/bin/env jbang "$0" "$@" ; exit $?
//JAVAC_OPTIONS --enable-preview -source 14 (1)
//JAVA_OPTIONS --enable-preview // (2)
import static java.lang.System.*;
public class records {
record Point(int x, int y) {}
public static void main(String[] args) {
var p = new Point(2,4);
out.println(p);
}
}Since Java 9 JDK_JAVA_OPTIONS and JDK_JAVAC_OPTIONS are also picked up by the Java runtime and compiler automatically.
For Java 8 and if you want to set explicitly only for jbang you can also add flags by setting JBANG_JAVA_OPTIONS and JBANG_JAVAC_OPTIONS respectively.
If JAVA_HOME environment variable is set that will be used over what is in the path.
Allows you to expliclity control what JDK you are using for jbang, i.e.
JAVA_HOME=~/sdkman/candidates/java/14.ea.302-open/bin/java jbang examples/records.java
This will use Java 14 from sdkman no matter what your PATH or JAVA_HOME contains in the shell environment.
If you are using bash or zsh in your terminal you can get auto-completion by running the following:
source <(jbang --completion)In previous versions of jbang Java 10+ direct launch of .java was used, but since v0.6 jbang works with Java 8 and thus it
needs to do a separate compile step. Besides now working with Java 8 it also allow us to cache the compile step and thus
launch faster on consecutive runs.
The caching goes to ~/.jbang by default, you can run jbang --clear-cache to remove all cache data from this folder.
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Why the name j’bang?
I was reading up on how to use the new shebang (#!) feature support in Java 10 and came up with the idea of port
kscriptto Java and needed a name. From there came j’bang which is a "bad" spelling of how shebang is pronounced in french. -
Why use gradle resource locators rather than ?
kscript used it and it’s nice as it is a one-liner and easily parsable.
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Why use of gradle resource locators rather than ?
kscript used it and its nice as it is a one-liner and easily parsable.
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How does this compare to ?
After doing
jbangI’ve learned about similar projects and thought it would be nice with some comparison;jgo: an alternative way to launch jars using maven coordinates. Implemented in python, depends on Java and Maven to be available. Not really for scripting but a novel way to launch java apps already packaged as a maven dependency.
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Why would I use Java to write scripts ? Java sucks for that… Use gradle, kotlin, scala, etc. instead!
Well, does it really suck ? With Java 8 streams, static imports and greatly improved standard java libraries it is very close to what kscript and grape look like. With the following advantages:
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works with plain Java without installing additional compiler/build tools
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all IDE’s support editing .java files very well, content assist etc.
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great debugging
And to be honest I built
jbangjust to see if I could and get my Java skills refreshed for the newer features in the language. Use it at your own risk :)
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Why not use normal shebang(
#!) in the header ?You can use normal shebang (
#!/usr/bin/env jbang) and Java 10+ will actually work with it from the command line. Not recommended though as many tools and especially IDE’s will start complaining about syntax errors as they don’t ignore the first line in this case.By using the
//form it is treated as both a bash/shell file AND a valid java file and thus works everywhere a java file will work.Its worth noting that Go uses a similar approach which is also where I learned it from.
jbang was heavily inspired by how kscript by Holger Brand works.