Load C++ Library Only Once

Django_Untaken

Hello there. I have managed to load and use c++ dll using JNI, in my java servlet (System.load). It works perfectly on first request I submit. But on subsequent requests, I get this weir d exception. java.lang.UnsatisfiedLinkError: Native Library WEB-INF/lib/XXXXXX.dll already loaded in another classloader at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1525) Here is my loading code

public void init(ServletConfig config) throws ServletException
{
super.init(config);
ServletContext context = getServletContext();
String sMathDllpath = context.getInitParameter("MathDLLPath");
System.load(sMathDllpath);

}

I studied this tomcat wiki link and implemented their solution, among others, but could not succeed. How do I implement it successfully? Thnks for anything you share.

Lost User

You should declare it as a static action at class level like:

class ... {
static
{
System.loadLibrary("MathDLLPath");
}
// remainder of your class
}

That will ensure it is loaded when the class is first instantiated, but will only be loaded once.

Django_Untaken

Richard MacCutchan wrote:

You should declare it as a static action at class level like:

I tried this just now. This is what I have

public class MainServlet extends HttpServlet
{
static{
System.loadLibrary("MathDll");
}

......... // rest of the class below this
}

And this is the exception I am getting java.lang.UnsatisfiedLinkError: Native Library C:\Program Files\Java\jdk1.7.0_71\bin\MathDll.dll already loaded in another classloader What am I doing wrong now?

Lost User

No idea, but it looks like you may have more than one call somewhere. Time to get the debugger out. Although, I have never used JNI in a servlet so it may be that there is something else happening.