How to Solve Java 9\'s \'Unable to derive module descriptor for auto generated module names\' Error?

Module Dependency Issue in Java 9: "Unable to derive module descriptor for auto generated module names"

The inability to derive a module descriptor for auto-generated module names in Java 9 arises when declaring dependencies on libraries that contain reserved keywords in their generated module names. Such is the case with Netty's Epoll transport, which generates a module name containing the "native" keyword.

Java 9 introduces the concept of modules, requiring explicit module declarations. However, auto-generated module names follow a convention that may include reserved keywords, leading to conflicts when explicitly declaring dependencies.

Solution:

To resolve this issue, two primary approaches are available:

1. Packaging with Automatic-Module-Name:

Libraries can package their artifacts with a META-INF/MANIFEST.MF file specifying the Automatic-Module-Name attribute. This attribute allows libraries to define a different module name than the generated one, which can avoid keyword conflicts.

2. Adding Module Declarations to JARs by Library Owners:

Library owners can add the necessary module declarations to their JAR files using a module-info.java file. This declares the explicit module dependencies and ensures compatibility with Java 9's module system.

Explanation:

Java's module declaration syntax specifies that module names must consist of valid Java identifiers. Reserved keywords, such as "native," are not allowed as identifiers, leading to the error message "Invalid module name: 'native' is not a Java identifier."

To address this, the Java module system specification suggests converting hyphens and other special characters to underscores and prefixing specific characters or keywords with underscores where necessary. However, it is important to note that underscores also became a keyword in Java 9, so their use as prefixes should be exercised cautiously.

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