GitHub user Sxnan created a discussion: Flink Agents Support Multi-JDK Versions
## Background
The Flink Agents project needs to support JDK 11 and above to ensure
compatibility with the Apache Flink ecosystem. However, some external
dependencies introduced in the project only support higher JDK versions, which
presents challenges for multi-JDK support.
Taking the `flink-agents-api` module as an example, this module introduces the
MCP (Model Context Protocol) SDK to support the MCP protocol, and **MCP SDK
only supports JDK 17+**. This means:
- If the released jar is compiled with JDK 17 and includes MCP code, JDK 11
users won't be able to use it due to class version incompatibility
- If the released jar is compiled with JDK 11 and excludes MCP code, JDK 17+
users won't be able to use MCP features
## Module-Specific Designs
### flink-agents-api
Since users depend on `flink-agents-api` via Maven, and this module as a
framework API is not suitable for shading external dependencies, the **Maven
Classifier** approach is adopted:
```plaintext
flink-agents-api-{version}-jdk11.jar # JDK 11 version, without JDK 17+
features
flink-agents-api-{version}-jdk17.jar # Default version, includes MCP and
other JDK 17+ features
```
#### Design Principles
1. **Default version ensures complete functionality**: The default jar (no
classifier) is compiled with JDK 17, ensuring all JDK 17+ users can use it
directly with JDK 17+ features
- **Lower JDK compatibility provided via classifier**: Users needing JDK
versions below 17 explicitly specify the classifier
1. **Unified dependency for the same module**: Users only need to depend on the
same artifactId, differentiating versions via classifier
#### User Usage
**JDK 11+ users (without MCP features)**
```xml
<dependency>
<groupId>org.apache.flink</groupId>
<artifactId>flink-agents-api</artifactId>
<version>${flink-agents.version}</version>
<classifier>jdk11</classifier>
</dependency>
```
**JDK 17+ users (need MCP features)**:
```xml
<dependency>
<groupId>org.apache.flink</groupId>
<artifactId>flink-agents-api</artifactId>
<version>${flink-agents.version}</version>
</dependency>
```
#### Version Contents
| Version | JDK Requirement | Included Content |
|---------|-----------------|------------------|
| jdk11 | JDK 11+ | Core API, Agent, Tool, Prompt, ChatModel, and other basic
features |
| Default (no classifier) | JDK 17+ | Basic features + MCP-related
implementations (MCPServer, MCPTool, MCPPrompt, etc.) |
### flink-agents-dist
`flink-agents-dist` is an uber jar distributed with the Python package; users
need to deploy it to the Flink cluster's lib directory. Because:
- dist itself is an uber jar that already shades all dependencies
- Python package distribution requires a single jar file
- Users don't depend on this module via Maven
The **Multi-release JAR** approach is adopted, where the JVM automatically
selects the correct classes based on version at runtime:
#### JAR Structure
```plaintext
flink-agents-dist-{version}.jar
├── org/apache/flink/agents/... # JDK 11 version classes (without
MCP)
├── (shaded common dependencies) # Common dependencies
└── META-INF/
└── versions/
└── 17/
├── org/apache/flink/agents/api/mcp/... # MCP-related classes
└── (shaded MCP SDK) # MCP SDK dependencies
```
#### Runtime Behavior
- **JDK 11 environment**: JVM loads classes from the root directory,
MCP-related code is ignored
- **JDK 17+ environment**: JVM preferentially loads classes from
`META-INF/versions/17/`, MCP features are available
#### Advantages
- **Transparent to users**: No configuration needed, JVM adapts automatically
- **Single jar distribution**: Python package only needs to include one jar file
- **Consistent architecture**: Follows the uber jar design philosophy of
shading all dependencies
### flink-agents-plan / flink-agents-runtime
These two modules **don't need** multi-JDK support:
- Users don't directly depend on these modules
- Source code uses reflection to call MCP classes, avoiding compile-time
dependencies
- Only test code involves JDK 17+ features, which doesn't affect the released
jar
### Other Modules
`integrations/*` and other modules currently have no JDK 17+ specific
dependencies and don't need multi-version support for now.
## Summary
| Module | Approach | Reason |
|--------|----------|--------|
| flink-agents-api | Maven Classifier | Users depend via Maven; API module not
suitable for shading external dependencies |
| flink-agents-dist | Multi-release JAR | uber jar already shades dependencies;
Python package needs single jar; transparent automatic adaptation for users |
| flink-agents-plan | Not needed | Users don't directly depend on it; uses
reflection to avoid compile-time dependencies |
| flink-agents-runtime | Not needed | Users don't directly depend on it; no JDK
17+ specific dependencies |
| integrations/\* | Not needed | Currently no JDK 17+ specific dependencies |
GitHub link: https://github.com/apache/flink-agents/discussions/405
----
This is an automatically sent email for [email protected].
To unsubscribe, please send an email to: [email protected]
