Unable to derive module descriptor for auto generated module names in Java 9?

问题

My project depends on Netty Epoll transport. Here is dependency:

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-transport-native-epoll</artifactId>
    <version>${netty.version}</version>
    <classifier>${epoll.os}</classifier>
</dependency>

The auto-generated module name for this dependency is:

netty.transport.native.epoll

And as the native keyword is reserved in Java 9 I can\'t add this module as a dependency to my project:

module core {
    requires netty.transport.native.epoll;
}

Due to:

module not found: netty.transport.<error>

Additionally the jar tool --describe-module reports the following:

Unable to derive module descriptor for: netty-transport-native-epoll-4.1.17.Final-SNAPSHOT-linux-x86‌_64.jar netty.transport.native.epoll: Invalid module name: \'native\' is not a Java identifier

Are there any workarounds? (except \"release correct netty artifact\", of course).

EDIT:

As the quick fix for maintainers - you can add next line to build:

<manifestEntries>
   <Automatic-Module-Name>netty.transport.epoll</Automatic-Module-Name>
</manifestEntries>

回答1:

Well, the solution to this seems to be:-

• renaming the artifact itself (might not be preferred by all owners)

  OR

• Another way possible to uninterruptedly using the same artifact name with a new(different) module name could be by packaging META-INF/MANIFEST.MF of the artifact with an attribute Automatic-Module-Name which governs the name of the module to be used by the module descriptor when converted as an automatic module.

  OR

• Artifact owner can add module declarations using module.info.java to their JAR. (this could result in a slow bottom-up migration)

---

Since the module declaration defined in the specs as:

A module declaration introduces a module name that can be used in other module declarations to express relationships between modules. A module name consists of one or more Java identifiers (§3.8) separated by "." tokens.

---

Intersetingly the declarations suggests -

In some cases, the Internet domain name may not be a valid package name. Here are some suggested conventions for dealing with these situations:

• If the domain name contains a hyphen, or any other special character not allowed in an identifier (§3.8), convert it into an underscore.

• If any of the resulting package name components are keywords (§3.9), append an underscore to them.

• If any of the resulting package name components start with a digit, or any other character that is not allowed as an initial character of an identifier, have an underscore prefixed to the component.

But keep in mind as you do so that Underscore is a keyword in Java9

int _;  // is would throw an error on javac based out of JDK9
int _native; // works fine

来源：https://stackoverflow.com/questions/46501388/unable-to-derive-module-descriptor-for-auto-generated-module-names-in-java-9