JNI - exception on native method

Question

I'm trying to use dll in my java application in eclipse, but I'm getting runtime exception whenever I try to call any method associated with that dll.

The dll exists in the following address, which I've passed in Run/Debug Settings in eclipse:

-Djava.library.path="C:\Program Files\NPortAdminSuite\ipserial\lib\x86;${env_var:PATH}"

Code:

class Test {

  public native int nsio_init();

  public static void main(String[] args) {
          System.loadLibrary("ipserial");
          new Test().nsio_init(); //This part is throwing an exception
  }
}

Error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: NPortConnection.nsio_init()I
    at Test.nsio_init(Native Method)
    at Test.main(Test.java:27)

The command dumpbin /exports "C:\Program Files\NPortAdminSuite\ipserial\lib\x86\IPSerial.dll" also returning me the name of method, which I'm trying to call from that dll enter image description here

Could anyone please tell how to solve this problem?

can you find any helpful information with either of hte following ? http://stackoverflow.com/a/1403808/774691 or http://stackoverflow.com/questions/8761979/unsatisfiedlinkerror-java-exception-when-the-class-with-the-native-method-is-not — john.k.doe, Jul 02 '12 at 05:57

dacwe · Accepted Answer · 2012-07-02T06:02:14.950

4

Looks like you are trying to call a dll function directly from java code. This is not possible (directly). You need to write a layer that translates between java and the native dll.

Have a look at these resources:

Another way around the problem is to use JNA, check out the wikipedia article for example.

edited Jul 02 '12 at 06:02

answered Jul 02 '12 at 05:56

dacwe

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score 2 · Answer 2 · edited May 23 '17 at 12:30

EDIT: See also this elegant answer using a function instead of the bottom preprocessor macro.

If you want to implement JNI, this is how I did:

Let's imagine the below class in file example.java:

package my.group.mypackage;

public class Example {
  static {
    System.loadLibrary("my-DLL-name");
  }

  public Example() {
    /* ... */
  }

  private native int    function1(int); //declare DLL functions
  private native String function2(int); //using the keyword
  private native void   function3(int); //'native'

  public void dosomething(int value) {
    int result = function1(value);  
    String str = function2(value);  //call your DLL functions
    function3(value);               //as any other java function
  }
}

Generate example.class from example.java (using javac or your EDI or maven...). Then generate C/C++ header file Java_my_group_mypackage_example.h from example.class using javah.

The declaration of C/C++ functions are in Java_my_group_mypackage_example.h. Now we implement the definition (body) of these functions in Java_my_group_mypackage_example.cpp for instance. Prefer using C++ (instead of C) to catch exceptions from other DLLs.

JNIEXPORT jlong JNICALL Java_my_group_mypackage_example_function1
  (JNIEnv *env, jobject object, jlong value)
{
  try 
  {
    /* ... my processing ... */
    return jlong(result);
  }
  CATCH_CPP_EXCEPTION_AND_THROW_JAVA_EXCEPTION
  return 0;
}

JNIEXPORT jstring JNICALL Java_my_group_mypackage_example_function2
  (JNIEnv *env, jobject object, jlong value)
{
  try 
  {
    /* ... my processing ... */
    jstring jstr = env->NewStringUTF("my result");
    return  jstr;
  }
  CATCH_CPP_EXCEPTION_AND_THROW_JAVA_EXCEPTION
  return 0;
}

JNIEXPORT void JNICALL Java_my_group_mypackage_example_function3
  (JNIEnv *env, jobject object, jlong value)
{
  try 
  {
    /* ... my processing ... */
  }
  CATCH_CPP_EXCEPTION_AND_THROW_JAVA_EXCEPTION
}

The C preprocessor macro CATCH_CPP_EXCEPTION_AND_THROW_JAVA_EXCEPTION is defined below. It converts the C++ exceptions into Java exceptions. Customize that code using your your own mypackage::Exception and put it in a common header (not in `Java_my_group_mypackage_example.h' because this could be regenerated again).

#define CATCH_CPP_EXCEPTION_AND_THROW_JAVA_EXCEPTION              \
                                                                  \
  catch (const mypackage::Exception& e)                           \
  {                                                               \
    jclass jc = env->FindClass("my/group/mypackage/Exception");   \
    if(jc) env->ThrowNew (jc, e.what());                          \
    /* if null => NoClassDefFoundError already thrown */          \
  }                                                               \
  catch (const std::bad_alloc& e)                                 \
  {                                                               \
    /* OOM exception */                                           \
    jclass jc = env->FindClass("java/lang/OutOfMemoryError");     \
    if(jc) env->ThrowNew (jc, e.what());                          \
  }                                                               \
  catch (const std::ios_base::failure& e)                         \
  {                                                               \
    /* IO exception */                                            \
    jclass jc = env->FindClass("java/io/IOException");            \
    if(jc) env->ThrowNew (jc, e.what());                          \
  }                                                               \
  catch (const std::exception& e)                                 \
  {                                                               \
    /* unknown exception */                                       \
    jclass jc = env->FindClass("java/lang/Error");                \
    if(jc) env->ThrowNew (jc, e.what());                          \
  }                                                               \
  catch (...)                                                     \
  {                                                               \
    /* Oops I missed identifying this exception! */               \
    jclass jc = env->FindClass("java/lang/Error");                \
    if(jc) env->ThrowNew (jc, "unidentified exception");          \
  }

Compile Java_my_group_mypackage_example.cpp to produce a DLL. Set your PATH or move that DLL within your java run-time directory (usually target).

Do not forget to replace "my-DLL-name" in the java source code by the name of your DLL without the extension (e.g. myname.dll -> "myname").

This also works using Linux/Unix shared library (*.so) ;-)

JNI - exception on native method

2 Answers2