Creating and Loading Shared Libraries

The Java^TM Tutorial

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Trail: Java Native Interface
Lesson: Writing a Java Program with Native Methods

Creating and Loading Shared Libraries

Procedures for creating and loading shared libraries are platform dependent. This page provides some answers regarding naming conventions for shared libraries and locating shared libraries.

Naming Conventions

Each Java runtime environment provides a platform-dependent mechanism for mapping between the actual file name of a shared library and the name string that you pass as an argument to the System.loadLibrary method.

Solaris:
The shared library file name requires a "lib" prefix and a ".so" extension. Do not include the "lib" prefix or the ".so" extension for the argument that you pass to the System.loadLibrary method.

Win32:
The shared library file name requires a ".dll" extension. Do not include the ".dll" extension for the System.loadLibrary method argument.

MacOS:
No special conventions.

Search Mechanisms

Each Java runtime environment provides its own mechanism that indicates where to find shared libraries for native method implementations. The platform-dependent wrapper script or application shell can use the appropriate mechanism to indicate where shared libraries are located.

Solaris:
The LD_LIBRARY_PATH environment variable defines a list of directories that the Solaris VM searches for shared libraries.

Win32:
The Win32 VM uses a search path that includes the current directory for the process or one of the directories listed in the PATH environment variable.

MacOS:
The Code Fragment Manager provides the search mechanism used by the MRJ VM to find and load a shared library. This search path includes the application folder that contains the Macintosh Java application shell generated by JBindery.

Avoiding Name Conflicts

To avoid file name conflicts, it is best to prepend directories or folders containing shared libraries to search paths, such as the LD_LIBRARY_PATH or PATH environment variables.

Supporting Multiple Platforms

Because a Java application with native methods may support multiple platforms, it helps to organize multiple shared libraries into sub-directories by platform, such as <app-dir>/lib/<platform>.

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