Running the processor with JDK 16 or newer requires a bit of extra configuration.
openapi-processor runs a java code formatter on the generated source code by default. Unfortunately it depends on internal jdk packages that are strongly encapsulated since JDK 16. It is necessary to export a few packages.
Running java from a cli it would look like this (from google-java-format):
java \ --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \ -jar ...
gradle configuration for JDK 16+
With gradle we can hide this in gradle.properties (sibling to build.gradle) by adding the following snippet:
org.gradle.jvmargs= \ --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \ --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
maven configuration for JDK 16+
With maven we can hide this in .mvn/jvm.config by adding the snippet:
--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
disabling the code formatter
Alternatively it is possible to skip the formatting step by disabling it in the options section of the mapping.yaml. The generated code will probably look a bit ugly…