How Can You Bundle Native and JNI Libraries in a Single JAR File?

Bundling Native and JNI Libraries in a JAR

Recently, a developer sought a means to consolidate multiple dependencies, including native libraries, within a single JAR file. This strategy aims to simplify distribution and reduce redistribution issues.

The Native Library Conundrum

One of the challenges encountered in this endeavor was the inclusion of the actual native library, as an existing attempt focused solely on the JNI library. Additionally, the prior solution appeared to be tailored for a specific native dependencies plugin and might not be suitable for general redistribution.

A Comprehensive Solution

The preferred approach involves utilizing System.load(File) to load the library instead of the conventional System.loadLibrary(String), which relies on the java.library.path system property. This method eliminates the need for users to install the library manually, but it may compromise portability across platforms if the JAR does not encapsulate all necessary libraries.

Implementation Process

1. Incorporate the native JNI libraries into the JAR at platform-specific locations, e.g., NATIVE/${os.arch}/${os.name}/libname.lib.

2. Implement code in a main class's static initializer to:

   • Determine the current os.arch and os.name.
   • Search for the library in the JAR at the predefined path using Class.getResource(String).
   • If the library is present, extract it to a temporary file and load it with System.load(File).

Case Study: jzmq

This solution was employed in jzmq, Java bindings for ZeroMQ, where hybrid functionality allows for fallback to searching for the library along the java.library.path if the embedded version cannot be loaded.

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