java-dev

Greg,

 These diagnostics helped me get unstuck and solve the problem.  
Thanks.  I also came to the conclusion that java support in Xcode is 
even more half baked than I previously believed.  For the reference of 
future readers (and my own records), I provide a full procedure for 
using Xcode to handle the C with a java wrapper side of the java native 
interface, and Eclipse to handle all of the other java.  Unfortunately, 
I do not know an easier way to get native macintosh code to run within java.

Using Xcode 3.0, OS 10.5.2, Eclipse 3.2.2.  With later versions this 
procedure will hopefully be simpler.

In advance, note that if you do not have reasonable grasp of C, Java, 
and Ant, this project will be difficult for you.  If you know C and 
Java, Ant is fairly easy to learn from Apache's tutorial.  Also see 
Sun's specification of the java native interface.

Note that in the following instructions, sometimes you right click, 
sometimes you click, sometimes you double click, sometimes you expand a 
tree, sometimes you select a tab or a menu item.  It is not always clear 
which is correct, so try all of them if necessary.

In Xcode:
1)  File -> New Project -> Java -> Java JNI Application -> XProjectName. 
2)  Run -> Console.
3)  Build and Go.  Verify that console output is:

[Session started at 2008-05-19 19:23:14 -0700.]
Started application
java.library.path = /Users/snld/xcode 
projects/XProjectName/build/Release:.:/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java
Instance created
shared_function called with Hello World !
Finished application. Answer is 42

The Debugger has exited with status 0.

4)  If you need frameworks, add them with Targets -> JNILib -> Link 
Binary With Library -> Right click -> Add -> Existing Frameworks.
5)  Real programmers use packages, so lets make one, no matter how 
difficult.  Right click src -> Delete -> Delete References
6)  CLOSE THE PROJECT
7)  Find your src folder in finder.  XProjectName.java and 
XProjectNamejnilib.c should be there.  If not, start over and this time 
delete the references, not the files.
8)  Create XProjectName/src/com/company/packageName.  Move 
XProjectName.java and XProjectNamejnilib.c into there.
9)  Reopen the Xcode project.  XProjectNamejnilib.c will be in red, 
because you moved it.  Right click it -> delete.
10)  Right click XProjectName.  Add existing files.  Select the src 
folder.  Ok.  Don't copy files into destination folder.  Reference Type: 
Default.  Text Encoding: Unicode.  Create folder References for any 
added folders.  Do not add to any targets.  We have to do that 
manually.  The folders should show up blue (this means you created 
folder references). 
11) Targets -> JNILib -> Compile Sources -> Right Click -> Add Existing 
File.  Select XProjectNamejnilib.c from your package folder.  Add to 
target JNILib, not XProjectName.
12) Open src/com/company/packageName.java.  Add package 
com.company.packageName; as the first line.
13)  Open build.xml.  Make the following changes:
       <!-- generate the header files -->
       <exec executable="/usr/bin/javah">
           <arg line="-classpath '${jarfile}' -force -d 
'${curr_header_dir}' *com.company.packageName.*XProjectName"/>
       </exec>

   <target name="run" depends="install">
       <java classpath="${jarfile}" 
classname="*com.company.packageName.*${ant.project.name}" fork="true">
           <sysproperty key="java.library.path" value="${dist}"/>
       </java>
   </target>

14) To PackageNamejnilib.c change to #include 
"*com_company_packageName_*XProjectName.h" to the top.

Change JNIEXPORT jint JNICALL 
Java*_com_company_packageName_*XProjectName_native_1method(JNIEnv *env, 
jobject this, jstring arg)

15) Double click Executables -> XProjectName.  Arguments tab.  Change 
Argument field to  -cp XProjectName.jar com.company.packageName.XProjectName

16) Run -> Console. 

Do you feel lucky?

17)  Build and Go.  Verify that the output is wrong.  Go back and figure 
out what went wrong and try again.

Useful tips:
Sometimes the build gets in a funny state, and needs to be cleaned.  
Build -> Clean All targets.  If this generates a lot of errors, that is 
a good thing because it means that the builder is paying attention.

javah (from the ant build) creates the header file 
com_company_packageName_XProjectName.h and puts it in the 
build/release/headers directory.  The prototypes here must match those 
in your testjnilib.c file.

The ant build only goes up to the install target when you use the build 
command in xcode.  To use ant fully, you must go to the command line, 
and type ant run (in the folder of build.xml).  It is often easier to 
get ant working outside of xcode than inside it.

From the terminal: nm libXProjectName.jnilib shows you its contents.  
Package names should be included.

Unsatisfield link Error means that your java code cannot find the native 
method or library in question.  Usually this is a naming or pathing problem.

Exception in thread "main" java.lang.NoClassDefFoundError: 
com/company/packageName/XProjectName means that your java initialization 
is not pointing to the main method correctly.  Check step 15, or the run 
line of your ant build if you are using run ant.

On to Eclipse:
1)  File -> New -> Java Project.  Name it EProjectName, and hit okay.
2)  Right click EProjectName.  New Package: com.company.packageName.  
Must have the same name as the package from xcode.
3)  Right Click the new package name.  New -> Class: XProjectName (the 
name of the Xcode project).   Click Finish.  Copy-Paste the contents 
from your xcode XProjectName.java to your eclipse XProjectName.java.
4)  Right click EProjectName -> New -> Folder -> jnilibs.  Use finder to 
copy the XProjectName/build/Release/libXProjectName.jnilib to this folder.
5) Right Click EProjectName -> Properties.  Java Build Path.  Source 
Tab.  EProjectName/src tree.  Double click Native Library Folder.  
Workspace.  Select the jnilibs folder that you just made.
6)  Hit the green Run arrow.  Verify that it is good.

Matthew

Greg Guerin wrote:
> Matthew Grivich wrote:
>
>   
> > I exited Xcode, and put my .java file in the src/edu/salk/snl/micrimap. I
> > reopened Xcode and noticed that it had updated properly. I recompiled (no
> > build errors) and ran. I still get the UnsatisfiedLinkError. I also tried
> > moving Grabberjnilib.c to the same location. This time, I had to re-add the
> > file to the project. Otherwise it was the same. Successful build and
> > UnsatisfiedLinkError.
> >     
>
> Post the stack-trace of the UnsatisfiedLinkError.
>
> Also, where are the jar file and the jnilib file located when the error occurs?
>
> Finally, run the 'nm' command on the jnilib file (in Terminal):
>   nm libYourNameHere.jnilib
> and post the output from that.
>
>
>   
> > Also, the automatically generated Grabber.h does not include any package
> > information.
> >     
>
> That may be causing the problem.
>
>
>   
> > The prototypes are of the form JNIEXPORT
> > jint JNICALL Java_Grabber_OpenCamera (JNIEnv *, jobject, jstring);
> >     
>
> That doesn't seem correct to me.  JNI binds classes to C functions by name,
> and that name includes a package.
>
>
>   
> > I don't know if this correct, but the
> > fact that the .jnilib works in Eclipse leads me to believe that it is.
> >     
>
> Can't tell.  Insufficient information.
>
> For example, Eclipse might be working because it's using older class files
> and jnilibs.  Can't tell unless you know exactly what files are in use when
> it works under Eclipse.
>
> You probably need to add diagnostic code that actually prints the entire
> class-name (anyObject.getClass()), so you can see whether you're using the
> class in the package or not.
>
> Other useful information is to print the java.class.path system property,
> along with the library path.  Heck, just print every system property, since
> the extensions-dirs will also affect loading of libs.
>
>   -- GG
>
>
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