subtask2 = scope.fork(task2);
scope.join();
} catch (Exception e) {
e.printStackTrace();
}
}
We can now develop our script as we would with any Java file.
A jar file : jbang export portable helloworld.java. If your script uses dependencies, the next commands are more recommended.
A fatjar : which contains all the dependencies: jbang export fatjar helloworld.java. This method still requires to install a JDK / JRE on the target machine. If you don't want to that, the next commands are more recommended.
A jlink binary that encompases a JDK: jbang export jlink helloworld.java. The binary to run is either helloworld-jlink/bin/helloworld on Unix or helloworld-jlink/bin/helloworld.bat on Windows.
A native imgae : jbang export native helloworld.java. This requires a GraalVM installation.
The script can also be exported as a mavenrepo with: jbang export mavenrepo helloworld.java
JDK management
As seen in a previous chapter, JBang can install JDKs on your machine.
Furthermore, it is possible to specify a JDK version in a scripts.
For example, the following script uses Java 25 and some preview features.
> jbang init helloworld.java
Scripts without a "Main" class
Since script tend to be lightweight, it would be preferable to write them without a class and a main method.
The following script will be compiled and executed without any problem.
> jbang helloworld.java
Hello world
This is made possible by adding the following properties to the script.
///usr/bin/env jbang "<pre class="brush:php;toolbar:false">> chmod +x helloworld.java
> ./helloworld.java
Hello world
" "$@" ; exit $?
import static java.lang.System.*;
public class helloworld {
public static void main(String... args) {
out.println("Hello world");
}
}
The first line, //JAVA 23 , tells JBang to use Java 23 or later.
Once the feature become stable, we can remove the 3 lines and the script will still work. Neat!
Dependencies
JBang supports adding dependencies to scripts in the form of Gradle style dependencies by adding a //DEPS atrefact-id:atrefact-name:version line for each dependency.
> jbang init helloworld.java
Catalogs
Catalogs in JBang allow to organize and share scripts and templates efficiently.
A catalog is a JSON file named jbang-catalog.json that contains two groups of items: aliases and templates.
JBang looks for local catalogs in these directories in the following order (source JBang docs):
Current directory, ./jbang-catalog.json
In ./.jbang/jbang-catalog.json
In the parent directory, ../jbang-catalog.json
In the parent’s .jbang directory, ../.jbang/jbang-catalog.json
And repeating steps 3 and 4 recursively upwards to the root of the file system
As the last step it will look in $HOME/.jbang/jbang-catalog.json
JBang will look for remote the catalogs in many open source repositories like GitHub, GitLab, Bitbucket, and others.
> jbang helloworld.java
Hello world
The following chapters will show how to use aliases and templates from a catalog.
Aliases
Aliases in JBang allow to run scripts from a catalog.
Aliases can be defined in the aliases section of the catalog file using the following format:
> jbang init helloworld.java
Here is the catalog I used during my session at DevoxxMA 2024.
> jbang helloworld.java
Hello world
You can run these aliases with the following commands:
jbang palcli@yostane/cours-java madam
jbang palqrest@yostane/cours-java
jbang hellojfx@yostane/cours-java
The official JBang GitHub account provides a catalog with many aliases and templates.
jbang httpd@jbangdev run a local webserver.
jbang gavsearch@jbangdev [arg] search for [arg] on search.maven.org.
Templates
Templates, which are pre-defined scripts that can be used as a starting point for new scripts.
///usr/bin/env jbang "<pre class="brush:php;toolbar:false">> chmod +x helloworld.java
> ./helloworld.java
Hello world
" "$@" ; exit $?
import static java.lang.System.*;
public class helloworld {
public static void main(String... args) {
out.println("Hello world");
}
}
When a template is used, JBang creates copies of all the files int the file-refs property.
Here are some examples of some templates available out of the box:
A CLI script that uses picocli: jbang init -t cli hellocli.java
A Quarkus single file REST API: jbang init -t qrest helloqrest.java
We can also use templates from the internet shared by the community.
/// usr/bin/env jbang "<pre class="brush:php;toolbar:false">///usr/bin/env jbang "<pre class="brush:php;toolbar:false">//JAVA 23+
//COMPILE_OPTIONS --enable-preview -source 23
//RUNTIME_OPTIONS --enable-preview
" "$@" ; exit $?
//JAVA 23+
//COMPILE_OPTIONS --enable-preview -source 23
//RUNTIME_OPTIONS --enable-preview
void main(String... args) {
System.out.println("Hello World");
}
" "$@" ; exit $?
//JAVA 25
//COMPILE_OPTIONS --enable-preview -source 25
//RUNTIME_OPTIONS --enable-preview
import java.util.concurrent.Callable;
import java.util.concurrent.StructuredTaskScope;
import static java.lang.System.*;
void main(String... args) {
out.println("Hello Java 25");
Callable task1 = () -> {
out.println("Task 1" + Thread.currentThread());
return "Task 1";
};
Callable task2 = () -> {
out.println("Task 2" + Thread.currentThread());
return 2;
};
try (
var scope = new StructuredTaskScope()) {
StructuredTaskScope.Subtask subtask1 = scope.fork(task1);
StructuredTaskScope.Subtask subtask2 = scope.fork(task2);
scope.join();
} catch (Exception e) {
e.printStackTrace();
}
}
App Store
The JBang App Store is a web app that allows to browse aliases of indexed catalogs.
Here are some interesting and funny scripts that I found by browsing on the the App Store:
Cowsay. Here are some examples of running the script:
jbang cowsay@ricksbrown/cowsay MOO!
jbang cowsay@ricksbrown/cowsay -f dragon "I'm Veldora Tempest!"
Find substring like grep: jbang grep@a-services "hello" .
Create PDF from images: images2pdf@a-services. The following commands will create a PDF file from two images:
///usr/bin/env jbang "<pre class="brush:php;toolbar:false"> {
"catalogs": {},
"aliases": {
// aliases
},
"templates": {
// templates
}
}
" "$@" ; exit $?
//DEPS com.github.lalyos:jfiglet:0.0.9
import com.github.lalyos.jfiglet.FigletFont;
public class DependenciesDemo {
public static void main(String... args) throws Exception {
System.out.println(FigletFont.convertOneLine("JBang is amazing"));
}
}
When you publish a catalog, it will very probably appear after the next indexing of the JBang AppStore.
Some examples with notable frameowrks
With JBang, we can create single file applications that use popular frameworks and libraries.
JavaFX (openjfx)
JavaFX is a desktop and UI framework.
Here are some examples JavaFX apps created with JBang:
Basic window
More beautiful example jbang https://gist.github.com/FDelporte/c69a02c57acc892b4c996a9779d4f830
A template jbang init -t javafx@yostane hellojfx
Quarkus
Quarkus is a Java framework that is optimized for Kubernetes and serverless environments.
Thanks to JBang, we can create single-file Quarkus applications that leverage the power of this framework.
> jbang init helloworld.java
We may notice a //SOURCES PalindromeService.java line in the script.
You can run the server with jbang palqrest@yostane/cours-java and call the endpoint with curl http://localhost:8080/palindrome?input=madam.
> jbang helloworld.java
Hello world
Other languages
JBang supports running Java, Kotlin, JShell and Groovy code.
Kotlin : You can initialize a Kotlin script with jbang init -t hello.kt filename.kt. Please note that this is different from the official .main.kts Kotlin scripts. In fact, Kotlin scripts created by JBang can benefit from the catalog and App Store features. Here is an example of a Kotlin script created with JBang.
> jbang init helloworld.java
Interesting fact: the idea of JBang came from kscript which is targeted to the Kotlin ecosystem.
Kotlin already has native scripting support (with .main.kts scripts) but seems to lack the catalog, template, and App Store features.
Groovy : Initialize a Groovy script with jbang init -t hello.groovy filename.groovy. Here is an example of a Groovy script created with JBang.
> jbang helloworld.java
Hello world
JShell : JBang supports JShell scripts with .jsh or .jshell extensions and inline scripts using jbang -c 'System.out.println("Inline Java ☕ yay!")'. Here is an example of a JShell script created with JBang.
///usr/bin/env jbang "<pre class="brush:php;toolbar:false">> chmod +x helloworld.java
> ./helloworld.java
Hello world
" "$@" ; exit $?
import static java.lang.System.*;
public class helloworld {
public static void main(String... args) {
out.println("Hello world");
}
}
Markdown with Java and JShell code blocks : You can run Java and JShell code blocks directly from a markdown file using jbang my_markdown.md.
/// usr/bin/env jbang "<pre class="brush:php;toolbar:false">///usr/bin/env jbang "<pre class="brush:php;toolbar:false">//JAVA 23+
//COMPILE_OPTIONS --enable-preview -source 23
//RUNTIME_OPTIONS --enable-preview
" "$@" ; exit $?
//JAVA 23+
//COMPILE_OPTIONS --enable-preview -source 23
//RUNTIME_OPTIONS --enable-preview
void main(String... args) {
System.out.println("Hello World");
}
" "$@" ; exit $?
//JAVA 25
//COMPILE_OPTIONS --enable-preview -source 25
//RUNTIME_OPTIONS --enable-preview
import java.util.concurrent.Callable;
import java.util.concurrent.StructuredTaskScope;
import static java.lang.System.*;
void main(String... args) {
out.println("Hello Java 25");
Callable task1 = () -> {
out.println("Task 1" + Thread.currentThread());
return "Task 1";
};
Callable task2 = () -> {
out.println("Task 2" + Thread.currentThread());
return 2;
};
try (
var scope = new StructuredTaskScope()) {
StructuredTaskScope.Subtask subtask1 = scope.fork(task1);
StructuredTaskScope.Subtask subtask2 = scope.fork(task2);
scope.join();
} catch (Exception e) {
e.printStackTrace();
}
}
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