Question

I have two sources:

• an xml-file containing definitions of several hundred data structures, basically structs with fields consisting of simple data types (e.g. int, short, boolean, enum), and
• a c header-file containing the same data structures represented a c structs. (I cannot modify this header-file or the c structs.)

I also have a library, written in c, that is able to use these c structs to perform a specific task.

Last I have a Java application which needs to use this library somehow.

Currently I generate Java classes from the xml-file representing the data structures, now I “just” need to provide them to the library somehow.

My current approach is to generate jni code, to call a c-function for each struct from Java, accepting the Java generated class as a parameter. Then generate c-code which takes the Java classes and fill in the appropriate fields in the c-structs.

Is this a good approach? Does anybody have suggestions for a simpler approach?

I am considering using sockets and e.g. protobuf, but I do not see this as any simpler.

Thanks in advance for any suggestions.

Answer 1

The solution I am ending up with is using the Javolution struct library

Basically I am generating Java classes that inherits the javolution.io.Struct class from the xml, and declaring the fields appropriately such that javolution can interpret it as struct.

This allows me to do a myJavaStructClass.getByteBuffer() and get a directly mapped byte buffer which has the same memory layout as if the Java “struct” where declared in c. And because it is directly mapped, contains a reference which can be passed directly to native code through JNI.

Javolution also supports both packed and non-packed structs, as well as arbitrary endianness.

Another solution would be to use SWIG to generate Java classes directly from the c header-files, and manage them directly in native code through JNI.