I recently wrote a webapp that leverages a proprietary application's api (in the form of a JNI wrapper api, so it requires a jar file and a set of system libraries/dlls) to allow interactions with this application using simple http calls.
Running my web application alone (placing the api jar in my webapp's WEB-INF/lib directory and the required system libraries somewhere in java.library.path) on Tomcat initially caused no problems, however when I attempt to run it alongside any web applications that also use the api I have all kinds of JNI errors. The first error I encountered occurred when I attempted to run my webapp after calling a second webapp that used the same api libraries. Depending on which webapp was executed first, it locked one of the system libraries and prevented the other from loading it (producing a java.lang.UnsatisfiedLinkError: Native Library x already loaded in another classloader). After some quick research into how the Tomcat classloader hierarchy works I was able to temporarily fix this by moving the api jar into shared/lib instead of into each of the webapps WEB-INF/lib directories. This ensures that the classes are loaded by a classloader that both webapps have access to. However, this is not a perfect fix. Firstly, on my "happycheck" page, I still obtain an UnsatisfiedLinkError when I check for the presence of a system library. My webapp still works, but the check fails. Currently I am just making a call to System.loadLibrary and catching any errors. Additionally, I would prefer to not have to dictate that other webapps remove their copy of the api jar from their WEB-INF lib directory. After some relatively extensive research, I have come to the understanding that the "java.lang.UnsatisfiedLinkError: Native Library x already loaded in another classloader" message is also displayed when the current classloader already has the system library loaded. So that explains the behavior of my happycheck page. Is there another way for me to check for the presence of a system library without just attempting to load it so that I can modify my happycheck Servlet to provide more accurate results? Also, is there a way that I can adjust my environment so that other webapps aren't required to move their api jar? I have tested and verified that the proprietary api jar uses System.loadLibrary and does not provide a way to specify an absolute path to the system libraries (if it did I could just copy the system libraries into my webapp directory and set a configuration item to describe where they are located). Therefore, about the only thing that I can think of is to somehow set the java.library.path for my webapp to be different then the one used for the other webapps. Is there a way to do this without having multiple Tomcat instances running? Other things that I tried include making calls to System.load for each of the system libraries in my webapp before I make any calls to the api. Unfortunately the System.loadLibrary call in the api jar still attempts to load the system library used by the other webapps. -- View this message in context: http://www.nabble.com/Best-Practice-for-UnsatisfiedLinkError%3A-Already-loaded-in-another-classl-tf2419784.html#a6746361 Sent from the Tomcat - User mailing list archive at Nabble.com. --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
