Re: GWT Native Code Deployment

Your DLL needs to go in one of the directories that are specified by
the 'java.library.path' system property, not in your classpath. The
classpath specifies the locations the jvm will look to load java
classes, not native code. I haven't really done any jni stuff in any
web applications I've done so I'm not real sure what the default
library path is in Tomcat.

On Nov 4, 8:03 am, Darin <daring90...@gmail.com> wrote:
> Hi, Adrian and Jeff.
>
> Thanks again for the help from both of you. I greatly appreciate it.
>
> I have two files in the server. One of them is SecurityServiceImpl and
> the code looks like this (skipping the includes, etc.):
> public class SecurityServiceImpl extends RemoteServiceServlet
> implements SecurityService {
>         private static NativeCodeClass nativeCode=new NativeCodeClass();
>         private CompressClass compression=new CompressClass();
>         @Override
>         public CompressedMessage validatePassword(CompressedMessage m) {
>                 String message=compression.Decompress(m);
>                 String username=message.substring(0,message.indexOf(','));
>                 String password=message.substring(message.indexOf(',')
> +1,message.length());
>                 String returnString=nativeCode.validatePassword(username, password);
>                 CompressedMessage replyMessage=compression.Compress(returnString);
>                 return replyMessage;
>         }}
>
> The other file is called NativeCodeClass and the code looks like this:
> public class NativeCodeClass {
>         static {
>                 System.loadLibrary("SolverLibrary");
>         }
>         public native String validatePassword(String username, String
> password);
>
> }
>
> I have doublechecked that both of these files are definitely in the
> server code (and these are the only files in the server code). When I
> run the code from within hosted mode, this code works (i.e. finds the
> SolverLibrary and checks the entered password, etc.). And (here comes
> the important part), when I compile it and run it from within the
> browser by pressing the Compile/Browse button from inside hosted mode,
> it works just fine as well inside Mozilla. It fails when I copy the
> directories to another place on the hard drive. Unless I am seriously
> confused (and I have to admit that this is a possibility), if the
> problem was one where the native code was executing inside of
> Javascript, it could not run correctly from inside the browser after
> the Compile/Browse step.
>
> It occurs to me that maybe my RPC calls to the server are not
> functioning correctly when I try to move the folders to somewhere else
> on the hard drive. Is there an obvious reason why that might happen?
> Thanks for all your help.
>
> Darin
>
> On Nov 4, 1:56 am, Adrian <ahay...@gmail.com> wrote:
>
> > Hi guys,
>
> > I think Darin might not be up to speed with the differences between
> > server side and client side stuff and also how web environment differs
> > from the desktop environment. You might know this already but if not
> > it might clear a few things up.
>
> > When developing an application with GWT in Eclipse you need to be
> > aware of two distinct parts, the client side and the server
> > side.Eclipse should setup a couple packages for these parts when you
> > create a GWT project so you don't get confused. The client side is
> > compiled from java to javascript that is designed to run only in a
> > browser. That means the resulting javascript has all the limitations
> > enforced by the browser, which includes no way to run native code. So
> > GWT compiles the java in the client package to javascript, which is
> > run in the browser once the browser requests it from your webserver
> > (apache in this case). Because apache isn't a java application server
> > (like tomcat, jetty etc) it cannot directly run the server side java
> > (stuff in the server package).
>
> > Things get a little confusing when you're running in hosted mode
> > because a lot of fancy stuff is happening in the background so it
> > appears the java code you have written for the client is running
> > directly, it basically skips the compiling to javascript step and runs
> > the client code as java. Because java has the ability to run native
> > code it will appear to work, however once compiled to javascript it
> > wont because javascript doesn't have the functionality (mainly for
> > security reasons).
>
> > Also don't be fooled by javascript's name, it is a very different
> > language than java!
>
> > So, you can't run native code from javascript in a browser, but you
> > can run it from java on the server side. A possibly solution could be
> > to use GWT's Remote Procedure Calls to run the native code on the
> > server, then get the results sent to back to the client.
>
> > Hope that helps,
> > Adrian
>
> > On Nov 4, 1:25 pm, Jeff Chimene <jchim...@gmail.com> wrote:
>
> > > On Tue, Nov 3, 2009 at 3:47 PM, Darin <daring90...@gmail.com> wrote:
>
> > > > Hi, Jeff. Again, thanks for the responses. I have researched what the
> > > > classpath means (and I assume you mean the directory or directories
> > > > where the JRE looks for possible libraries to use)
>
> > > Yes
>
> > > > and I have manually
> > > > set the classpath to be the directory where the library resides.
> > > > Unfortunately, that still did not change anything.
>
> > > I didn't expect it would.
>
> > > > To the best of my knowledge, the server itself isn't supposed to run
> > > > the code.
>
> > > The code that you posted originally (the call to LoadLibrary) should only
> > > run on the server. It might also run on the client in hosted mode, but
> > > that's not what you want in the Long Run.
>
> > > According to the GWT website (please correct me if I am
>
> > > > wrong, and it is very possible that I am wrong), the code is executed
> > > > as Javascript from within the browser.
>
> > > Correct, as long as you;re not trying to call LoadLibrary.
>
> > > The Javascript that is already
>
> > > > theoretically executing from within the browser is supposed to execute
> > > > the native code.
>
> > > I don't know what you mean by "native code". Do you mean the compiled C++
> > > code in SolverLibrary? If so. the browser will not execute that native code
> > > (at least not via GWT compiled Javascript)
>
> > > For some reason, it finds the code on the computer on
>
> > > > which I am developing the app, but cannot find the native code when I
> > > > copy it directly to another machine (into the directory where Apache
> > > > looks for its source files). I have copied the SolverLibrary into
> > > > every subdirectory of the main Apache library that I can find but the
> > > > native code still refuses to execute. I'm going to try installing
> > > > Eclipse and GWT on the server machine and see if that helps. Wish me
> > > > luck...
>
> > > I think we're back to the issue that Apache doesn't have a JRE, so it's not
> > > finding the code that calls LoadLibrary. I think that what's happening is
> > > that in hosted mode, you're using Tomcat, a Java server which will find and
> > > execute the code that calls LoadLibrary. When you move to GWT noserver mode,
> > > then you're using Apache.
>
> > > What is the error you get when you run the code using an Apache server
> > > instance?
>
> > > > Best, Darin
>
> > > > On Nov 3, 2:14 pm, Jeff Chimene <jchim...@gmail.com> wrote:
> > > > > Hi Darin:
>
> > > > > After re-reading your first post, I think you're already in a
> > > > client-server
> > > > > environment. I am confused by the following:> I am running Windows XP and
> > > > using Apache as my http server. Any ideas for
>
> > > > > where I should put the native library so
>
> > > > > > that the Javascript can find it?
>
> > > > > Your Apache installation probably doesn't run Java
> > > > > I think the reason it works in hosted mode is that your hosted mode
> > > > server
> > > > > is a Java server: Tomcat.
>
> > > > > On Tue, Nov 3, 2009 at 2:59 PM, Jeff Chimene <jchim...@gmail.com> wrote:
>
> > > > > > On Tue, Nov 3, 2009 at 2:36 PM, Darin <daring90...@gmail.com> wrote:
>
> > > > > >> Hi, Jeff.
>
> > > > > >> Thank you so much for responding to my question.
>
> > > > > >> Perhaps I'm getting confused by the jargon. The "SolverLibrary" that I
> > > > > >> wrote is written in C/C++ and compiled by Visual Studio into a DLL.
> > > > > >> This DLL is supposed to be run only on the server. The GWT code was
> > > > > >> written in Eclipse and follows essentially the documentation on the
> > > > > >> GWT web site. At the moment, the C/C++ DLL is only checking whether a
> > > > > >> username and password sent it by the client exists within a file on
> > > > > >> the server (nothing fancy; there is no reason to do this in C/C++
> > > > > >> other than to see if it will work) though I have plans to make much
> > > > > >> more complicated native functions once I get this to work. I am not
> > > > > >> sure where the "classpath" is. There is an environment variable in
> > > > > >> Windows called the "PATH"; is that what you mean? I do call the
> > > > > >> library via RPC. The calling code is as follows (written in Java in
> > > > > >> Eclipse using GWT):
>
> > > > > >> public class SecurityServiceImpl extends RemoteServiceServlet
> > > > > >> implements SecurityService {
>
> > > > > >>        private static NativeCodeClass nativeCode=new
> > > > NativeCodeClass();
> > > > > >>        private CompressClass compression=new CompressClass();
> > > > > >>        @Override
> > > > > >>        public CompressedMessage validatePassword(CompressedMessage m)
> > > > {
> > > > > >>                String message=compression.Decompress(m);
> > > > > >>                String
> > > > username=message.substring(0,message.indexOf(','));
> > > > > >>                String password=message.substring(message.indexOf(',')
> > > > > >> +1,message.length());
> > > > > >>                String
> > > > returnString=nativeCode.validatePassword(username,
> > > > > >> password);
> > > > > >>                CompressedMessage
> > > > > >> replyMessage=compression.Compress(returnString);
> > > > > >>                return replyMessage;
> > > > > >>        }
> > > > > >> }
>
> > > > > >> Again, thanks for your help. Any other suggestions would be welcome.
> > > > > >> Best, Darin
>
> > > > > >> All the above has to run on the server (because it uses classes
> > > > defined in
> > > > > > SolverLibrary). You'll want to modify the above to handle requests from
> > > > your
> > > > > > client for solver library routines. The code you've posted so far will
> > > > only
>
> ...
>
> read more »
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