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javatomcatdlljna

Extract DLL from within JNA jar file to a custom path

The production environment our Java Web Application is deployed in has several permission restrictions, one of them being unable to write in drive C:

We recently added jna-4.1.0.jar and jna-platform-4.1-0.jar dependencies to be able to read Windows Registry but I've noticed that every time server (Tomcat v7.0) is started a DLL file is extracted to a Tomcat temporary folder, giving the following error:

java.lang.UnsatisfiedLinkError: C:\Program Files\Apache Software Foundation\Tomcat 7.0\temp\jna-1319675979\jna1892288885647543043.dll: The handle is invalid

I've verified that this same DLL is extracted successfully when access permission restriction is removed to ensure this is the source of my problem, but I want to know if there is any way to specify a custom path where that DLL must be extracted to, since we are able to write in drive E:, for example.

Solution

  • The DLL you're seeing is JNA's JNI library used to dispatch native calls [0]. JNA will extract the library to a temporary folder, unless found from the directory specified by the jna.boot.library.path property [1], or with System.loadLibrary [2].

    The directory used for temporary items can be set with the jna.tmpdir property [3]. For example:

    java -jar program.jar -Djna.tmpdir=E:/temp

    If jna.tmpdir is not set, JNA will use java.io.tmpdir.

    Notice that at the time of writing, JNA will use File.mkdirs() to create the directory structure of the tmpdir, so you don't need to make sure the folders exist.