API Signature Check jlink Plug-in

A proof-of-concept for a plug-in for the jlink tool which detects differences between the API exposed by a module added to a custom Java runtime image and other modules calling this API. This helps to prevent NoSuchMethodErrors at application runtime, caused by using different versions of a module at compile time vs. runtime.

Note: The jlink plug-in API is currently not officially supported nor exposed by the jdk.jlink module. Hence some trickery is required for compiling and using this plug-in.

Usage

Build the project as described below. Then create a custom runtime image for the example modules:

$JAVA_HOME/bin/jlink \
  -J-javaagent:agent/target/signature-check-jlink-plugin-registration-agent-1.0-SNAPSHOT.jar \
  -J--module-path=plugin/target/signature-check-jlink-plugin-1.0-SNAPSHOT.jar:/Users/gunnar/.m2/repository/org/codehaus/mojo/animal-sniffer/1.19/animal-sniffer-1.19.jar:/Users/gunnar/.m2/repository/org/ow2/asm/asm/9.0/asm-9.0.jar \
  -J--add-modules=dev.morling.jlink.plugins.sigcheck \
  --module-path=$JAVA_HOME/jmods/:example/customer-2/target/customer-2-1.0-SNAPSHOT.jar:example/order/target/order-1.0-SNAPSHOT.jar \
  --add-modules=com.example.order \
  --output=target/runtime-image \
  --check-signatures

The order module is compiled against the customer-1 module. The runtime image is created using the customer-2 module though, which contains a breaking API change. When not using this plug-in, this would result in a NoSuchMethodError at runtime. With this plug-in, the mismatching API signature will be detected at link time and raised as an error:

[ERROR] /com.example.order/com/example/order/OrderService.class:13: Undefined reference: void com.example.customer.CustomerService.doIt(String)
Error: Signature violations, check the logs

Implementation

This is a very basic PoC, using Animal Sniffer internally for creating and comparing API signatures. Only a subset of API changes will be spotted, e.g. an added abstract method to a superclass or interface would not be detected and still result in an error at runtime.

Build

This project requires OpenJDK 11 or later for its build. Apache Maven is used for the build. Run the following to build the project:

mvn clean install

License

This code base is available under the Apache License, version 2.