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Camel JBang Self-Executing Launcher

dsl/camel-jbang/camel-launcher/README.md

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Camel JBang Self-Executing Launcher

This module provides a self-contained executable JAR that includes all dependencies required to run Camel JBang without the need for the JBang two-step process.

The launcher uses Spring Boot's loader tools to create a self-executing JAR with a nested structure, similar to Spring Boot's executable JARs. This provides better performance and avoids classpath conflicts compared to traditional fat JARs.

Building

To build the fat-jar launcher:

bash
mvn clean package

This will create:

  1. A self-executing JAR (camel-launcher-<version>.jar) in the target directory using Spring Boot's nested JAR structure
  2. Distribution archives (camel-launcher-<version>-bin.zip and camel-launcher-<version>-bin.tar.gz) in the target directory

Usage

Using the JAR directly

bash
java -jar camel-launcher-<version>.jar [command] [options]

For example:

bash
java -jar camel-launcher-<version>.jar version
java -jar camel-launcher-<version>.jar run hello.java

Using the distribution

  1. Extract the distribution archive:

    bash
    unzip camel-launcher-<version>-bin.zip
# or
tar -xzf camel-launcher-<version>-bin.tar.gz

  2. Use the provided scripts:

    bash
    # On Unix/Linux
./bin/camel.sh [command] [options]

# On Windows
bin\camel.bat [command] [options]

Benefits

  • No need for JBang installation
  • Single executable JAR with all dependencies included
  • Faster startup time (no dependency resolution step, on-demand class loading)
  • Better memory usage (only loads classes that are actually used)
  • Avoids classpath conflicts (dependencies kept as separate JARs)
  • Each self-executing JAR is its own release, avoiding version complexity
  • Can still be used with JBang if preferred

JAR Structure

The launcher uses Spring Boot's nested JAR structure:

camel-launcher-<version>.jar
 |
 +-META-INF
 |  +-MANIFEST.MF (Main-Class: org.springframework.boot.loader.launch.JarLauncher)
 +-org
 |  +-springframework
 |     +-boot
 |        +-loader
 |           +-<spring boot loader classes>
 +-BOOT-INF
    +-classes
    |  +-org/apache/camel/dsl/jbang/launcher/CamelLauncher.class
    |  +-<other application classes>
    +-lib
       +-camel-jbang-core-<version>.jar
       +-camel-main-<version>.jar
       +-<other dependency JARs>

This structure provides better performance and reliability compared to traditional fat JARs where all classes are merged together.