Including a JRE with Eclipse Products

How It Works

When includeJRE="true" is set in your product file:

1. It automatically resolves the appropriate JRE based on the product's target environments
2. The JRE is included in the final product materialization and archives

This approach leverages the p2 dependency resolution mechanism, making it the most integrated and streamlined solution.

Prerequisites

To use automatic JRE inclusion, you only need:

1. Set includeJRE="true" in your product file

That's it! Tycho automatically fetches the JRE from the default JustJ repository.

Configuration Example

Step 1: Set includeJRE="true" in your product file

<?xml version="1.0" encoding="UTF-8"?>
<?pde version="3.5"?>

<product name="My Application" 
         uid="my.application.product" 
         id="my.application.product" 
         application="org.eclipse.ui.ide.workbench" 
         version="1.0.0" 
         type="features" 
         includeLaunchers="true" 
         includeJRE="true">
   
   <!-- Your product configuration -->
   <features>
      <feature id="org.eclipse.platform" installMode="root"/>
      <!-- Your other features -->
   </features>
   
</product>

That's all you need! When includeJRE="true" is set, Tycho automatically:

• Fetches the appropriate JRE from the JustJ repository (https://download.eclipse.org/justj/jres)
• Resolves the correct JRE version based on your product's target environments
• Includes the JRE in the final product

Customizing the JRE Repository (Optional)

By default, Tycho uses the JustJ repository at https://download.eclipse.org/justj/jres. If you need to use a different JRE source or disable automatic JRE fetching, you can configure the productRepository parameter in the tycho-p2-director-plugin:

<plugin>
  <groupId>org.eclipse.tycho</groupId>
  <artifactId>tycho-p2-director-plugin</artifactId>
  <version>${tycho-version}</version>
  <configuration>
    <!-- Use a specific JustJ version repository -->
    <productRepository>https://download.eclipse.org/justj/jres/21/updates/release/</productRepository>
    
    <!-- Or disable automatic JRE fetching entirely -->
    <!-- <productRepository></productRepository> -->
  </configuration>
</plugin>

Choosing a JustJ JRE Version

By default, Tycho uses the base JustJ repository (https://download.eclipse.org/justj/jres) which provides JREs for multiple Java versions. If you need a specific Java version, you can configure the productRepository parameter as shown above.

Common JustJ repository options:

• Default (all versions): https://download.eclipse.org/justj/jres
• Java 17 specific: https://download.eclipse.org/justj/jres/17/updates/release/
• Java 21 specific: https://download.eclipse.org/justj/jres/21/updates/release/

Configuration Example

Step 1: Include JRE feature in your product file

<?xml version="1.0" encoding="UTF-8"?>
<?pde version="3.5"?>

<product name="My Application" 
         uid="my.application.product" 
         version="1.0.0" 
         type="features" 
         includeLaunchers="true">
   
   <features>
      <!-- Include JustJ JRE feature explicitly -->
      <feature id="org.eclipse.justj.openjdk.hotspot.jre.full"/>
      
      <!-- Your application features -->
      <feature id="org.eclipse.platform" installMode="root"/>
      <!-- Your other features -->
   </features>
   
</product>

Step 2: Add JustJ repository to your pom.xml

<repositories>
  <repository>
    <id>justj</id>
    <url>https://download.eclipse.org/justj/jres/21/updates/release/</url>
    <layout>p2</layout>
  </repository>
</repositories>

Step 3: Configure target platform

<plugin>
  <groupId>org.eclipse.tycho</groupId>
  <artifactId>target-platform-configuration</artifactId>
  <version>${tycho-version}</version>
  <configuration>
    <executionEnvironment>none</executionEnvironment>
  </configuration>
</plugin>

When to Use Manual Inclusion

The manual approach is useful when:

• You want explicit control over which JRE feature variant is included
• You're migrating from an older product configuration
• You need to include additional JRE-related features or fragments

JRE Not Found During Build

Problem: Tycho cannot resolve the JRE during product materialization when using automatic inclusion.

Solutions:

• Ensure the includeJRE="true" attribute is present in your product file
• Check that the productRepository parameter is configured correctly (if customized)
• Verify internet connectivity to download from the JustJ repository

Problem: Tycho cannot resolve the JRE when using manual feature inclusion.

Solutions:

• Verify that your JustJ repository URL is correct and accessible in the <repositories> section
• Check that executionEnvironment is set to none in target-platform-configuration to avoid conflicts

Multiple JRE Versions Resolved

Problem: Multiple JRE versions are being resolved, causing conflicts.

Solutions:

• When using automatic inclusion: Configure a specific JRE version via the productRepository parameter
• When using manual inclusion: Specify only one JustJ repository in your <repositories> section
• Review your target platform configuration to ensure no conflicting JRE sources

Product Fails to Launch

Problem: The product builds successfully but fails to launch on the target system.

Solutions:

• Verify the JRE architecture (x86_64, aarch64) matches your product's target environment
• Check that the product's launcher is correctly configured to use the bundled JRE
• Ensure the JRE version is compatible with your Eclipse platform and plugins

Understanding executionEnvironment=none (Manual Method Only)

Why is this needed for manual JRE inclusion?

When manually including JRE features in your product, you need to set executionEnvironment=none in the target-platform-configuration.

By default, Tycho injects mock “a.jre” units into the target platform to satisfy Java package imports (like javax.xml, java.util, etc.) and execution environment requirements. These mock units don't provide an actual JRE—they're just markers for dependency resolution.

When you explicitly add JustJ features to your target platform, which provides real JRE bundles with the same capabilities, you get conflicts. Setting executionEnvironment=none tells Tycho: “Don't inject your mock JRE units; I'm providing a real JRE through my target platform.”

Note: This is NOT needed for automatic JRE inclusion with includeJRE="true", as Tycho handles the JRE outside of the target platform.

Can I use a different JRE provider instead of JustJ?

Yes, you can use any JRE provider that publishes JRE artifacts as p2 installable units. The key requirement is that the JRE provider must supply p2 IUs with the appropriate capabilities.

Does includeJRE="true" work with all operating systems?

Yes, Tycho automatically resolves the appropriate JRE for each target environment. JustJ provides JRE distributions for Windows, macOS, and Linux on various architectures (x86_64, aarch64).

What's the difference between jre.full and other JRE features?

This question applies to the manual JRE inclusion method. JustJ provides different JRE feature variants:

• org.eclipse.justj.openjdk.hotspot.jre.full - Complete JRE with all modules
• org.eclipse.justj.openjdk.hotspot.jre.minimal - Minimal JRE for reduced size

Choose based on your application's Java module requirements. Most applications should use the full variant unless you have specific size constraints and know your exact module dependencies.

How do I include JREs for multiple platforms?

Tycho automatically handles multi-platform builds. Simply define multiple target environments in your target-platform-configuration:

<plugin>
  <groupId>org.eclipse.tycho</groupId>
  <artifactId>target-platform-configuration</artifactId>
  <version>${tycho-version}</version>
  <configuration>
    <environments>
      <environment>
        <os>win32</os>
        <ws>win32</ws>
        <arch>x86_64</arch>
      </environment>
      <environment>
        <os>linux</os>
        <ws>gtk</ws>
        <arch>x86_64</arch>
      </environment>
      <environment>
        <os>macosx</os>
        <ws>cocoa</ws>
        <arch>x86_64</arch>
      </environment>
    </environments>
  </configuration>
</plugin>

Tycho will automatically resolve and include the appropriate JRE for each platform when includeJRE="true" is set.