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Can JNA be used for a complex Windows DLL like IMAPI

I've managed to get COM4J to use some functionality in the windows IMAPI (CD writing).
However I've failed to get any of the calls that return SAFEARRAYs working, but this project doesn't appear to be currently active ...
The DLL is usually in C:\Windows\System32\imapi2.dll, and using it also requires using C:\Windows\System32\imapi2fs.dll
Looking around for a JAVA-COM bridge project that is active led me to JNA.
The remit of the project to simplify JAVA-COM bridging intrigued me .... however I fell at the first hurdle, and am hoping someone can help.
So far I've taken the Microsoft IMAPI examples and written a Powershell application, from which I have the series of calls I need to make to the API.[CDInterface][1]
The first thing you need to do with IMAPI is create an Instance of IDiskMaster2, so I've declared that via an Imapi2 interface, like so
public interface Imapi2 extends Library {
Imapi2 INSTANCE = (Imapi2)
Native.load("C:/Windows/System32/imapi2.dll" , Imapi2.class);
public static class IDiscMaster2 extends Structure {
int getCount;
public int getCount() {
return getCount;
}
}
IDiscMaster2 createMsftDiscMaster2();
}
Then in the main code
Imapi2.IDiscMaster2 recorderList = Imapi2.INSTANCE.createMsftDiscMaster2();
System.out.println("Found " + recorderList.getCount() + " Recorders");
Just putting 'imapi2' in the call to Native.load() didn't work either.
I'm guessing I'm doing something fundamentally wrong, but it's not clear how you get JNA to 'see' a new dll you want to interface to ..... and also I am kind of afraid there is something very different about this API from the othe APIs that people are using JNA to talk to, so may not be worth trying!
public interface Imapi2 extends Library {
Imapi2 INSTANCE = (Imapi2)
Native.load("C:/Windows/System32/imapi2.dll" , Imapi2.class);
public class IDiscMaster2 extends Dispatch {
public static final CLSID CLSID_MsftDiscMaster2 = new CLSID("2735412F-7F64-5B0F-8F00-5D77AFBE261E");
public IDiscMaster2() {
}
private IDiscMaster2(Pointer pvInstance) {
super(pvInstance);
}
public static IDiscMaster2 create() {
PointerByReference pbr = new PointerByReference();
WinNT.HRESULT hres = Ole32.INSTANCE.CoCreateInstance(CLSID_MsftDiscMaster2, null, WTypes.CLSCTX_ALL, null, pbr);
if (COMUtils.FAILED(hres)) {
System.out.println("ERROR: Failed to create instance");
return null;
}
return new IDiscMaster2(pbr.getValue());
}
public WinNT.HRESULT _getCount(Pointer count ){
return (WinNT.HRESULT) _invokeNativeObject(2, new Object[]{count}, WinNT.HRESULT.class);
}
public long getCount() {
try {
long count = -1;
Pointer ptr = new Pointer(count);
WinNT.HRESULT result = _getCount(ptr);
COMUtils.checkRC(result);
return count;
} catch ( Exception e ) {
System.out.println("Error : " + e.getMessage());
}
return -1;
}
}
Then invocation in main changed to
Imapi2 imapi2Lib = Imapi2.INSTANCE;
Imapi2.IDiscMaster2 recorderList = new Imapi2.IDiscMaster2();
System.out.println("Found " + recorderList.getCount() + " Recorders");
IntelliJ shows up uninvoked methods, so it doesn't look like create() is getting called. Not sure if this is because I need to call it, or down to the function implementing IDispatch not IUnknown.
[1]: https://github.com/nosdod/CDInterface

I've answered this in a similar question which I originally marked this as a duplicate of. However, given the difficulty loading this, your case is unique enough that I'll attempt to give a separate answer.
The general case for COM is that there is an API function that creates the object. You have mapped this as createMsftDiscMaster2(). Note that you have allocated a resource here and it needs to be disposed of when you are done with it; the API documentation should tell you how to do that (possibly by calling Release() from IUnknown.)
Your next step is to map the IDiscMaster2 COM class. I see two mappings here, so I'm confused as to which one you want. The one at the top of your question is incorrect, but the one extending Dispatch later is the correct way to start, but I'm not clear where you've gone after that. The rest of the class should look similar to the internals of the Dispatch class in JNA.
In that class you can see the boilerplate that you will follow. Note that it extends Unknown which follows the same boilerplate for offsets 0, 1, and 2 for the first 3 COM functions QueryInterface, AddRef, and Release. Dispatch picks up with offsets 3, 4, 5, and 6 for COM functions GetTypeInfoCount, GetTypeInfo, GetIDsOfNames, and Invoke.
So in your mapping for DiskMaster2 you will pick up with offset 7, and your mapping will look like:
public HRESULT TheFunctionName(FOO foo, BAR bar) {
return (HRESULT) this._invokeNativeObject(7,
new Object[] { this.getPointer(), foo, bar },
HRESULT.class);
}
This is where you need to locate the actual header file for this class to determine the order in which the functions appear in the Vtbl. It looks like you attempted to do this with your code, but the offset 2 is already assigned in Unknown, the lowest one you'll be able to use is 7 (and continue on with 8, 9, 10 for each function in this COM interface, in the correct order -- which you must determine from the Vtbl.)
Based on this header, you can see those functions mapped in order and your offsets should be: 7: get__NewEnum, 8: get_Item, 9: get_Count, and 10: get_IsSupportedEnvironment. Use those header function mappings as a start and change them to the _invokeNativeObject() format above. (They all return HRESULT, you'll just be changing the argument list.)

What is the best way to determine the number of GDI objects within a Java program?

We had the task to periodically check the number of GDI objects a Java process is using on a Windows machine. We had a leak issue leak issue using some third party library. When a certain limit is reached, the application more or less crashes. You can see them in the Windows task manager when you add the GDI-Objects column.
Since we didn't find an existing method we ended up using JNA-Platform-library to get access to the GetGuiResources API function of the user32.dll.
We did the following:
extended User32-interface and added a corresponding method
created an INSTANCE of the extended interface using Native.loadLibrary()
called the method of the INSTANCE by using Kernel32.INSTANCE.GetCurrentProcess() and DWORD(0)
The code now looks like this:
public class GdiTester {
private static interface ExtendedUser32 extends User32 {
/**
* Provides access to the user32.dll-API-Function GetGuiResources.
*
* #param hProcess the process
* #param uiFlags flags (e.g. 0 to get the number of GDI-objects)
* #return result of the API-function call (e.g. the number of GDI-objects)
*/
DWORD GetGuiResources(HANDLE hProcess, DWORD uiFlags);
}
private static ExtendedUser32 INSTANCE = Native.loadLibrary("user32", ExtendedUser32.class, W32APIOptions.DEFAULT_OPTIONS);
public static void main(String[] args) {
System.out.println("Number of GDI-objects: " + INSTANCE.GetGuiResources(Kernel32.INSTANCE.GetCurrentProcess(), new DWORD(0)).intValue());
}
}
Do you know an other (better) way to do this?

How to find number of live objects in a Java application without using any tool? [duplicate]

This question already has an answer here:
How to get jmap histogram programmatically?
(1 answer)
Closed 7 years ago.
Is there a way to find no. of alive objects of a class at any point of time in a running application? By alive/live objects, I mean those objects which are NOT eligible for garbage collection. Is there any way to find it without using any tools?
Assume that the entire application is personally coded. So the classes can be customised as per our need. Also, assume that the class whose live instance count we want to find, is a user defined class, not any inbuilt class.

The simple answer is no - there is no simple class or method call to make to find this data. However, there are many ways that people have come up with. It depends on why you need the data and the structure of your program.
There are good discussions on this topic here: http://www.coderanch.com/t/581790/java/java/ways-find-number-alive-instances and here: How to find the number of objects in the heap.
Give some of those a try and see which works best for you.

Yes.
Create a class based static instance counter that is synchronous
Up it by one in the class method(s) that instantiate..
Then u will have to override the dispose method to decrement instance counter..
UPDATE
Here is a nebulous class.. that can be used to track some things...
package myclasses;
import java.util.Vector;
public class ClassA {
private static int iCountInstances = 0;
private static int iCountCleanups = 0;
private static int iCountGCFinalize = 0;
private String m_str1 = null;
private Vector m_vct1 = null;
public ClassA() {
// bump the instance count
incrementCountInstance();
}
private static synchronized void incrementCountInstance() {
iCountInstances++;
}
private static synchronized void incrementCountCleanup() {
iCountCleanups++;
}
private static synchronized void incrementGCFinalize() {
iCountGCFinalize++;
}
/**
* reportOut - you can change this up on how ever you like
*
* an in control app in a perfect world will have all three counts THE SAME after a final
* GC and right before exist.
*
* The True number of 'active' classes in an app is going to be
* ICountInstances - iCountGCFinalize.
*
* The idea here is that if GC did not dispose of it.. its still in memory.. and still
* active.. even if your app thinks its no longer using it...
*
* #return
*/
public static String reportOut() {
return "ClassA Counts: incnt:" + ClassA.iCountInstances +", clncnt:" + ClassA.iCountCleanups + ", gccnt:" + ClassA.iCountGCFinalize;
}
public void cleanup() {
//
// ok.. initialize all member variables here
// do not worry about what other object refereneces this guy
// you only care about what you have as member variables.
// you only de-refrence what you point to ..
// if every class took care of what it referenced.. then all is well.
// so.. clean up your object and help GC ...
this.setM_str1(null);
this.getM_vct1().removeAllElements();
ClassA.incrementCountCleanup(); // Increment the cleanup count..
//
// feel free to write to a logger reporting out that programmer has cleaned up this instance..
//
}
#Override
protected void finalize() throws Throwable
{
// Incrementing means GC determined this guy is truly an Object Orphan and has been
// completely de-referenced.
ClassA.incrementGCFinalize();
//
// feel free to write to a logger reporting out that GC is removing this instance..
//
}
public String getM_str1() {
return m_str1;
}
public void setM_str1(String m_str1) {
this.m_str1 = m_str1;
}
public void setM_vct1(Vector m_vct1) {
this.m_vct1 = m_vct1;
}
public Vector getM_vct1() {
return m_vct1;
}
}
Here is another class that can be made to help report out whats going on during execution.. etc..
package myclasses;
public final class CheckCounts {
// No create instance allowed..
private CheckCounts() {
}
/**
* Report out on interesting counts...
*/
public static void reportOut() {
/// Add all the reportouts here..
System.out.println(ClassA.reportOut());
}
}
You can get fancy with this and create a background thread monitor that simply reports out stats on the classes you want to track.. and have it write to a logger every 30 seconds or so..
Notice I count up everything. You can use math to see how effective your code is at cleaning up after itself.. When you clean up an object.. you want to dereference what that objected pointed to and clear out any lists, arrays, hashmaps, etc. Be careful though, dont go crazy, and start cleaning up objects that live in a Vector of your class - just clean up the vector itself...
Give it a try.. its easy to implement.. and it may help you see whats going on in a runtime env vs what you think is happening just by looking at your code..

Wrapper Classes for Backward compatibility in Java

There is an interesting article here on maintaing backwards compatibility for Java. In the wrapper class section, I can't actually understand what the wrapper class accomplishes. In the following code from MyApp, WrapNewClass.checkAvailable() could be replaced by Class.forName("NewClass").
static {
try {
WrapNewClass.checkAvailable();
mNewClassAvailable = true;
} catch (Throwable ex) {
mNewClassAvailable = false;
}
}
Consider when NewClass is unavailable. In the code where we use the wrapper (see below), all we have done is replace a class that doesn't exist, with one that exists, but which can't be compiled as it uses a class that doesn't exist.
public void diddle() {
if (mNewClassAvailable) {
WrapNewClass.setGlobalDiv(4);
WrapNewClass wnc = new WrapNewClass(40);
System.out.println("newer API is available - " + wnc.doStuff(10));
}else {
System.out.println("newer API not available");
}
}
Can anyone explain why this makes a difference? I assume it has something to do with how Java compiles code - which I don't know much about.

The point of this is to have code which is compiled against some class which may not be available at runtime. WrapNewClass has to be present in the classpath of javac, or this thing can't be compiled. However, it can be absent from the classpath at runtime.
The code you quote avoids references to WrapNewClass if mNewClassAvailable is false. Thus, it will just print the 'new API not available' message.
However, I can't say that I'm impressed. In general, I've seen this sort of thing arranged with java.lang.reflect instead of trying to catch the exception. That, in passing, allows the class to be nowhere in sight even when compiled.

I have long had the need to support every JVM since 1.1 in JSE and have used these kind of wrapping techniques to compatibly support optional APIs - that is, APIs which make the application work better, but are not essential to it.
The two techniques I use seem to be (poorly?) described in the article you referenced. Rather than comment further on that, I will instead provide real examples of how I have done this.
Easiest - Static Wrapper Method
Need: To invoke an API if it is available, or otherwise do nothing. This can be compiled against any JVM version.
First, set up a static Method which has the reflected method, like so:
static private final java.lang.reflect.Method SET_ACCELERATION_PRIORITY;
static {
java.lang.reflect.Method mth=null;
try { mth=java.awt.Image.class.getMethod("setAccelerationPriority",new Class[]{Float.TYPE}); } catch(Throwable thr) { mth=null; }
SET_ACCELERATION_PRIORITY=mth;
}
and wrap the reflected method instead of using a direct call:
static public void setImageAcceleration(Image img, int accpty) {
if(accpty>0 && SET_ACCELERATION_PRIORITY!=null) {
try { SET_ACCELERATION_PRIORITY.invoke(img,new Object[]{new Float(accpty)}); }
catch(Throwable thr) { throw new RuntimeException(thr); } // exception will never happen, but don't swallow - that's bad practice
}
}
Harder - Static Wrapper Class
Need: To invoke an API if it is available, or otherwise invoke an older API for equivalent, but degraded, functionality. This must be compiled against the newer JVM version.
First set up a static wrapper class; this may be a static singleton wrapper, or you might need to wrap every instance creation. The example which follows uses a static singleton:
package xxx;
import java.io.*;
import java.util.*;
/**
* Masks direct use of select system methods to allow transparent use of facilities only
* available in Java 5+ JVM.
*
* Threading Design : [ ] Single Threaded [x] Threadsafe [ ] Immutable [ ] Isolated
*/
public class SysUtil
extends Object
{
/** Package protected to allow subclass SysUtil_J5 to invoke it. */
SysUtil() {
super();
}
/** Package protected to allow subclass SysUtil_J5 to override it. */
int availableProcessors() {
return 1;
}
/** Package protected to allow subclass SysUtil_J5 to override it. */
long milliTick() {
return System.currentTimeMillis();
}
/** Package protected to allow subclass SysUtil_J5 to override it. */
long nanoTick() {
return (System.currentTimeMillis()*1000000L);
}
// *****************************************************************************
// STATIC PROPERTIES
// *****************************************************************************
static private final SysUtil INSTANCE;
static {
SysUtil instance=null;
try { instance=(SysUtil)Class.forName("xxx.SysUtil_J5").newInstance(); } // can't use new SysUtil_J5() - compiler reports "class file has wrong version 49.0, should be 47.0"
catch(Throwable thr) { instance=new SysUtil(); }
INSTANCE=instance;
}
// *****************************************************************************
// STATIC METHODS
// *****************************************************************************
/**
* Returns the number of processors available to the Java virtual machine.
* <p>
* This value may change during a particular invocation of the virtual machine. Applications that are sensitive to the
* number of available processors should therefore occasionally poll this property and adjust their resource usage
* appropriately.
*/
static public int getAvailableProcessors() {
return INSTANCE.availableProcessors();
}
/**
* Returns the current value of the most precise available system timer, in milliseconds.
* <p>
* This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock
* time. The value returned represents milliseconds since some fixed but arbitrary time (perhaps in the future, so
* values may be negative). This method provides millisecond precision, but not necessarily millisecond accuracy. No
* guarantees are made about how frequently values change. Differences in successive calls that span greater than
* approximately 292,000 years will not accurately compute elapsed time due to numerical overflow.
* <p>
* For example, to measure how long some code takes to execute:
* <p><pre>
* long startTime = SysUtil.getNanoTick();
* // ... the code being measured ...
* long estimatedTime = SysUtil.getNanoTick() - startTime;
* </pre>
* <p>
* #return The current value of the system timer, in milliseconds.
*/
static public long getMilliTick() {
return INSTANCE.milliTick();
}
/**
* Returns the current value of the most precise available system timer, in nanoseconds.
* <p>
* This method can only be used to measure elapsed time and is not related to any other notion of system or wall-clock
* time. The value returned represents nanoseconds since some fixed but arbitrary time (perhaps in the future, so values
* may be negative). This method provides nanosecond precision, but not necessarily nanosecond accuracy. No guarantees
* are made about how frequently values change. Differences in successive calls that span greater than approximately 292
* years will not accurately compute elapsed time due to numerical overflow.
* <p>
* For example, to measure how long some code takes to execute:
* <p><pre>
* long startTime = SysUtil.getNanoTick();
* // ... the code being measured ...
* long estimatedTime = SysUtil.getNanoTick() - startTime;
* </pre>
* <p>
* #return The current value of the system timer, in nanoseconds.
*/
static public long getNanoTick() {
return INSTANCE.nanoTick();
}
} // END PUBLIC CLASS
and create a subclass to provide the newer functionality when available:
package xxx;
import java.util.*;
class SysUtil_J5
extends SysUtil
{
private final Runtime runtime;
SysUtil_J5() {
super();
runtime=Runtime.getRuntime();
}
int availableProcessors() {
return runtime.availableProcessors();
}
long milliTick() {
return (System.nanoTime()/1000000);
}
long nanoTick() {
return System.nanoTime();
}
} // END PUBLIC CLASS

I've seen this behaviour in spring and richfaces. Spring, for example, does the following
has a compile-time dependency on JSF
declares a private static inner class where it references the JSF classes
try/catches Class.forName(..) a JSF class
if no exception is thrown, the inner class is referenced (and the spring context is obtained through the faces context)
if exception is thrown, the spring context is obtained from another source (the servlet context)
Note that inner classes are not loaded until they are referenced, so it is OK to have a dependency that is not met in it.
(The spring class is org.springframework.web.context.request.RequestContextHolder)

Wrapping an existing application with JNI

Most of the documentation that details how to get started with JNI described how to build a new JNI application using X-Code. Can anyone link me to a description of how to use JNI to interface with Objective-C in an existing application.

NOTE: I have completely re-written this answer from scratch, now that I know for sure it works ;-).
Use Rococoa instead of JNI.
Here is a brief sample I was able to whip up that displays the picture taker dialog (based on your comment to Stephen C's answer).
/***
* INCOMPLETE: Doesn't have imports or anything like that.
***/
public interface Quartz extends Library
{
public static Quartz instance = (Quartz)Native.loadLibrary("Quartz", Quartz.class);
}
public interface IKPictureTaker extends NSObject
{
public static final _Class CLASS = Rococoa.createClass("IKPictureTaker", _Class.class);
public interface _Class extends NSClass
{
/**
* Returns a shared {#code IKPictureTaker} instance, creating it if necessary.
* #return an {#code IKPictureTaker} object.
*/
IKPictureTaker pictureTaker();
}
NSInteger runModal();
}
public class IKPictureTakerTest extends JFrame
{
public static void main(String[] args) throws Exception
{
// You need a GUI before this will work.
new IKPictureTakerTest().setVisible(true);
NSAutoreleasePool pool = NSAutoreleasePool.new_();
// Initialize the Quartz framework.
Quartz.instance.toString();
// Display the dialog.
IKPictureTaker pictureTaker = IKPictureTaker.CLASS.pictureTaker();
NSInteger result = pictureTaker.runModal();
if (result.intValue() == 0) // NSCancelButton
{
System.out.println("User cancelled.");
}
else
{
assert result.intValue() == 1; // NSOKButton
System.out.println("User chose an image.");
}
System.out.println(pictureTaker.inputImage()); // null if the user cancelled
pool.release();
}
}
If you get lost, try the Rococoa mailing lists. The developers are very helpful.

You will still need to write a JNI library of some sort to wrap your access to the existing code (aka, shared object, DLL, service program, etc). This is because JNI requires a rather obtuse (but sensible) naming convention for the native functions invoked, because you need to move data in and out of Java memory space and because you need to have conceptual "bridging" code between Java and your native function.
For example, I wrote a JNI library to provide access to existing C functions on the iSeries. One such function to read from a data area looks as follows:
JNIEXPORT void JNICALL Java_com_xxx_jni400_DataArea_jniGetDataArea(JNIEnv *jep, jobject thsObj, jbyteArray qulnam, jint str, jint len, jbyteArray rtndta, jint rtnlen) {
jbyte *qn,*rd;
Qwc_Rdtaa_Data_Returned_t *drt;
QFBK2_T fbk;
byte nam[11],lib[11];
byte *ptr;
// SETUP
thsObj=thsObj;
qn=(*jep)->GetByteArrayElements(jep,qulnam,0);
rd=(*jep)->GetByteArrayElements(jep,rtndta,0);
fbk.pro=sizeof(fbk); fbk.avl=0;
// INVOKE
QWCRDTAA(rd,rtnlen,(byte*)qn,str,len,&fbk);
// HANDLE SUCCESSFUL INVOCATION
if(fbk.avl==0) {
drt=(Qwc_Rdtaa_Data_Returned_t*)rd;
if(drt->Length_Value_Returned>0) { /* pad with spaces until the length requested */
ptr=(byte*)(rd+sizeof(*drt)+drt->Length_Value_Returned);
for(; drt->Length_Value_Returned<len; drt->Length_Value_Returned++,ptr++) { *ptr=' '; }
}
}
// RELEASE JAVA MEMORY LOCKS
(*jep)->ReleaseByteArrayElements(jep,qulnam,qn,JNI_ABORT); /* discard array changes */
(*jep)->ReleaseByteArrayElements(jep,rtndta,rd,0 ); /* copy back changes */
// TRANSFORM NATIVE ERROR INTO AN EXCEPTION AND THROW
if(fbk.avl!=0) {
byte eid[8],dta[201];
word dtalen;
f2s(nam,sizeof(nam),(byte*)qn ,10);
f2s(lib,sizeof(lib),(byte*)(qn+10),10);
dtalen=(word)mMin( sizeof(fbk.dta),(fbk.avl-(sizeof(fbk)-sizeof(fbk.dta))) );
f2s(eid,sizeof(eid),fbk.eid,sizeof(fbk.eid));
f2s(dta,sizeof(dta),fbk.dta,dtalen);
if(mStrEquI(eid,"CPF1015") || mStrEquI(eid,"CPF1021")) {
throwEscape(jep,90301,"Could not find data area %s in library %s",nam,lib);
}
else if(mStrEquI(eid,"CPF1016") || mStrEquI(eid,"CPF1022")) {
throwEscape(jep,90301,"Not authorized to data area %s in library %s",nam,lib);
}
else if(mStrEquI(eid,"CPF1063") || mStrEquI(eid,"CPF1067")) {
throwEscape(jep,90301,"Cannot allocate data area %s in library %s",nam,lib);
}
else if(mStrEquI(eid,"CPF1088") || mStrEquI(eid,"CPF1089")) {
throwEscape(jep,90301,"Substring %i,%i for data area %s in library %s are not valid",str,len,nam,lib);
}
else {
if(strlen(dta)>0) { throwEscape(jep,90001,"System API QWCRDTAA returned error message ID %s (%s)",eid,dta);}
else { throwEscape(jep,90001,"System API QWCRDTAA returned error message ID %s",eid); }
}
}
}
Note the one-line invocation for underlying existing API, QWCRDTAA, which is provided by IBM; the rest is Java-centric wrapping which is necessary to make the call and deal with the results.
Also, be very careful that what you invoke is thread-safe, or that you protect the code from concurrent invocations globally in the Java layer, or that you protect the code with a mutex in the O/S layer.
PS: Note that non-threadsafe native code is globally non-threadsafe; you must prevent concurrent invocation with all other non-threadsafe native code, not just the one method you are invoking. This is because it might be unsafe due to an underlying call to some other function which other unsafe methods call (like strerror(), (if my C memory serves well)).

Assuming that the Object-C application can be run via the command line, a simpler (and less problematic) approach would be to launch it using one of the java.lang.Runtime.exec(...) methods.
JNI is fraught with complexity and stability issues, and it is best to avoid it if you can.
EDIT: The OP has explained that this is a "widget" not a command line application. That makes it harder to avoid using JNI. But I still think that you ought to try. For example, you could consider wrapping the Objective-C widget in an Objective-C application, that runs the widget in a new window.