How to transfer a C structure to java by use of JNI?

Question

From C I am creating a DLL which is loaded in Java. I call some C functions from java and also call Java functions from C (whith uncomplex data types) - this is working fine.

I struggle with the transfer of a C structure to Java.

Here is a small example descriping what I want to do. It is not complete and maybe not correct because my problem is that I am not sure how to do it.

My goal is to pass a structure from the type "StructType" from C to Java in order to use the values in the Java program.

In C

typedef struct {
  unsigned char value1;
  unsigned char value2;
} StructType;

void passStructToJava(StructType* myStruct)
{
  class cls;
  jmethodID mid;

  /* GlobalEnv, GlobalObj are globlal values which are already set */
  cls = (*GlobalEnv)->GetObjectClass(GlobalEnv, GlobalObj); 
  mid = (*GlobalEnv)->GetMethodID(GlobalEnv, cls, "receiveStructFromC", "(LPackage/StructType;)V");

  (*GlobalEnv)->CallVoidMethod(GlobalEnv, GlobalObj, mid, myStruct);
}

In Java

 public class StructType {
 public int value1; /* int because there is no uint8 type */
 public int value2;
}

public StructType mMyStruct;
public StructType getMyStruct() {
  return mMyStruct;
}
public void setMyStruct(StructType myStruct) {
  mMyStruct = myStruct;
}


public void receiveStructFromC(StructType myStruct)
{
  setMyStruct(myStruct);
}

Thanks in advance for your help.
Steffen

Answer 1

Check my post in this question: pass data between Java and C