Problem with JNI on Linux

Howard <>
Wed, 24 Jan 2007 14:18:12 -0500
I am having a problem getting JNI to work on Linux. I think it is with
how I am creating the shared object file. I am using Java 1.5.0_8 and
Redhat Enterprise version 3 release 4. I have not used JNI before so I
did a web search and found a simple example that I am trying to get to
work. The problem is that I am getting an UnsatisfiedLinkError. It looks
like there are many flavors of this error and I can get at least three
of them :(

My Java program is:

class FirstJNI
     public native void displayHelloWorld();
     public native void displayOther();
     public native String getLine(String prompt);

     static {
       System.out.println("in static");

     public static void main(String[] args)
       System.out.println("entered main");
       System.out.println("creating new FirstJNI");
       FirstJNI jN=new FirstJNI();

       String input = jN.getLine("Enter Some Thing ");
       System.out.println("You Entered " + input);

and my c library is:

#include "FirstJNI.h"
#include <stdio.h>

Java_FirstJNI_displayHelloWorld(JNIEnv *env, jobject obj)
     printf("Hello world! \n");

Java_FirstJNI_displayOther(JNIEnv *env, jobject obj)
     printf("Hello world! This is Other Function.\n");

Java_FirstJNI_getLine(JNIEnv *env, jobject obj, jstring enter)
     char buf[128];
     const char *str = (*env)->GetStringUTFChars(env, enter, 0);
     printf("%s", str);
     (*env)->ReleaseStringUTFChars(env, enter, str);

     scanf("%s", buf);
     return (*env)->NewStringUTF(env, buf);

I am building them with the following commands:

/usr/java/jdk1.5.0_08/bin/javah -jni FirstJNI
gcc -O2 -I/usr/java/jdk1.5.0_08/include
-I/usr/java/jdk1.5.0_08/include/linux -fno-strict-aliasing -fPIC
-fno-omit-frame-pointer -W -Wall -Wno-unused -Wno-parentheses -c FirstJNI.c
gcc -Wl, -shared-libgcc -lc -shared -o FirstJNI.o

If I then try and run it (after setting my LD_LIBRARY_PATH) I get:

[hsr@palain8 jni]$ /usr/java/jdk1.5.0_08/bin/java FirstJNI
in static
Exception in thread "main" java.lang.UnsatisfiedLinkError:
/users/hsr/apache-tomcat-4.1.32/webapps/perf/jni/ cannot
open shared object file: No such file or directory
         at java.lang.ClassLoader$NativeLibrary.load(Native Method)
         at java.lang.ClassLoader.loadLibrary0(
         at java.lang.ClassLoader.loadLibrary(
         at java.lang.Runtime.loadLibrary0(
         at java.lang.System.loadLibrary(
         at FirstJNI.<clinit>(

This is strange since it is giving me a fully qualified path and if I do
an ls of that path the file is there. So, just for fun I removed the
file, tried again and got:

[hsr@palain8 jni]$ /usr/java/jdk1.5.0_08/bin/java FirstJNI
in static
Exception in thread "main" java.lang.UnsatisfiedLinkError: no FirstJNI
in java.library.path
         at java.lang.ClassLoader.loadLibrary(
         at java.lang.Runtime.loadLibrary0(
         at java.lang.System.loadLibrary(
         at FirstJNI.<clinit>(

This indicates to me that in the first example it really knew the file
was there and that there was something else wrong. Next I went to the
demo directory of the java 1.5.0_8 install and grabbed an .so file out
of there and copied t to my directory. Now I get:

[hsr@palain8 jni]$ /usr/java/jdk1.5.0_08/bin/java FirstJNI
in static
entered main
creating new FirstJNI
Exception in thread "main" java.lang.UnsatisfiedLinkError: displayHelloWorld
         at FirstJNI.displayHelloWorld(Native Method)
         at FirstJNI.main(

This is exactly what I would expect and the fact that this time it found
the .so indicates to me that it has nothing to do with my misnaming the
methods. So, I can only conclude that it is seeing my .so but not
recognizing it as valid which indicates that I am not linking it correctly.

After this long winded posting does anyone have any words of wisdom or



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