JNA: java.lang.Error: Invalid memory access - TS3 Library

Question

I'm using JNA to access some dll function from Java, this dll Native Function is declared as the following:

unsigned int ts3client_initClientLib(const struct ClientUIFunctions* functionPointers, const struct ClientUIFunctionsRare* functionRarePointers, int usedLogTypes, const char* logFileFolder, const char* resourcesFolder);

and so, I declared it inside library interface as the following:

int ts3client_initClientLib(Structure functionPointers, Structure functionRarePointers, int usedLogTypes, String logFileFolder, String resourcesFolder);

and then I call it the following way:

ts3client_initClientLib(null, null, 1, "log.log", "soundbackends");

but I'm getting the following Exception:

Exception in thread "main" java.lang.Error: Invalid memory access
    at com.sun.jna.Native.invokeInt(Native Method)
    at com.sun.jna.Function.invoke(Function.java:383)
    at com.sun.jna.Function.invoke(Function.java:315)
    at com.sun.jna.Library$Handler.invoke(Library.java:212)
    at com.sun.proxy.$Proxy0.ts3client_initClientLib(Unknown Source)
    at pl.edu.tirex.ts3musicbot.MusicBot.main(MusicBot.java:17)

Most likely the target function wants a non-NULL structure populated with callbacks where you're giving it a NULL pointer. — technomage
– technomage, Commented Jun 6, 2015 at 22:20

Szymon · Accepted Answer · 2017-03-05 22:54:02Z

Correct solution:

Create event interface:

import com.sun.jna;

public interface ServerErrorEvent implements Callback
{
    void invoke(long serverConnectionHandlerID, String errorMessage, int error, String returnCode, String extraMessage);
}

Create Client UI Functions Structure:

import com.sun.jna.Structure;

public class EventsStructure extends Structure
{
    public ServerErrorEvent onServerErrorEvent;

    @SuppressWarnings("rawtypes")
    @Override
    protected List<String> getFieldOrder() 
    {
        List<String> fields = new ArrayList<String>();
        for (Field f : this.getClass().getDeclaredFields())
        {
            boolean has = false;
            for (Class<?> c : f.getType().getInterfaces())
            {
                if (c.equals(DefaultEvent.class))
                {
                    has = true;
                }
            }
            if (has)
            {
                fields.add(f.getName());
            }
        }
        return fields;
    }
}

Use following methods:

EventsStructure eventStructure = new EventsStructure();
eventStructure.onServerErrorEvent = new ServerErrorEvent() //implement server error event
{
    @Override
    public void invoke(long serverConnectionHandlerID, String errorMessage, int error, String returnCode, String extraMessage)
    {
        System.out.println("server error");
    }
};
ts3client_initClientLib(eventStructure, null, 0, "logs", "soundbackends"); //invoke ts3client_initClientLib function from library

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