Am trying to call a x86 DLL that I created using VC 6, from a java project on Eclipse, first try I got an error saying that I can't call a x86 DLL from a x64 envirement and that the DLL can't be loaded. So I installed a x86 jre and I have no more problem to charge the DLL.
But when I try to call my c++ function I get the following exception:
Exception in thread "main" java.lang.UnsatisfiedLinkError: mm.SimpleDLL.SimpleDLL_Calculation_Add(II)I
Can someone please help me ?
Thank you.
SimpleDLL.h
#ifndef SIMPLE_DLL_H
#define SIMPLE_DLL_H
namespace SimpleDll
{
extern class Calculation
{
public:
static __declspec(dllexport) int Add(int a, int b);
};
}
#endif SIMPLE_DLL_H
SimpleDLL.cpp
#include "SimpleDll.h"
namespace SimpleDll
{
int Calculation::Add(int a, int b)
{ return a + b; }
}
SimpleDLL.java
package mm;
public class SimpleDLL {
static
{
System.load("D:\\SimpleDLL.dll");
}
public static void main(String ar[])
{
System.out.println("Hello world from Java");
SimpleDLL t=new SimpleDLL();
int x = t.SimpleDLL_Calculation_Add(6, 7);
System.out.println("Resultat "+x);
}
public native int SimpleDLL_Calculation_Add(int a, int b);
}
Exported DLL Functions View
Resolved using the JNA library, I used this link to walkthrough
You need to build a 32-bit DLL and a .h file using javah for the exact signature Java expects. It is usually something like
JNIEXPORT jboolean JNICALL Java_Sample1_booleanMethod
(JNIEnv *, jobject, jboolean);
from https://medium.com/#bschlining/a-simple-java-native-interface-jni-example-in-java-and-scala-68fdafe76f5f
An alternative approach is to use a library like JNA or JNR-FFI which allow you to bind to a C library without writing this bridging code.
Related
I have a simple C# class library, I wrapped it in a C++/CLI class library and loaded it into a simple Java console application. But when I run the Java application, I get the following error:
Process is terminated due to StackOverflowException.
Process finished with exit code -1073741571 (0xC00000FD)
My C# library has a Class1.cs file:
using System;
namespace CSharpClassLibrary1
{
public class Class1
{
public Class1() { }
public void Print()
{
Console.WriteLine("Hello World From C#!");
}
}
}
My C++/CLI wrapper has two files: HelloWorld.h and CppClassLibrary1.cpp.
HelloWorld.h:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class HelloWorld */
#ifndef _Included_HelloWorld
#define _Included_HelloWorld
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: HelloWorld
* Method: print
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_HelloWorld_print
(JNIEnv*, jobject);
#ifdef __cplusplus
}
#endif
#endif
I got it by running the command of the following form in my Java application: javac -h <directory> -d <directory> <source files>.
CppClassLibrary1.cpp:
#include "pch.h"
#include "HelloWorld.h"
using namespace CSharpClassLibrary1;
JNIEXPORT void JNICALL Java_HelloWorld_print(JNIEnv* env, jobject obj)
{
Class1^ cls = gcnew Class1();
cls->Print();
}
I added the CSharpClassLibrary1 as reference to the C++/CLI wrapper.
I added to the "Include directories" setting the following paths:
C:\Users\ns16\AppData\Local\JetBrains\Toolbox\apps\IDEA-C\ch-0\192.6817.14\jbr\include
C:\Users\ns16\AppData\Local\JetBrains\Toolbox\apps\IDEA-C\ch-0\192.6817.14\jbr\include\win32
My Java application has a HelloWorld.java file:
public class HelloWorld {
public native void print();
static {
try {
System.loadLibrary("CppClassLibrary1");
} catch (UnsatisfiedLinkError e) {
System.err.println("Native code library failed to load.\n" + e);
}
}
public static void main(String[] args) {
HelloWorld hw = new HelloWorld();
hw.print();
}
}
I specified the CppClassLibrary1 library path in the java.library.path variable.
Please help me! What am I doing wrong?
Update. A study of the problem showed the following:
In the Java application error appears in the hw.print(); line. If you comment it out, the application will start successfully.
If in the C++/CLI wrapper in the CppClassLibrary1.cpp file you replace Java_HelloWorld_print function body to the std::cout << "Hello World From C++/CLI!"; line, the Java application will start successfully and print the Hello World From C++/CLI! string.
If you create C# console application, add to it the C# library as references and add into Main method the Class1 cls = new Class1(); cls.print(); code, the application will start successfully and print the Hello World From C#! string.
I copied the C# library assembly in the directory with the java.exe file (in my system it located in C:\Users\ns16\AppData\Local\JetBrains\Toolbox\apps\IDEA-C\ch-0\192.6817.14\jbr\bin) and now the Java application works! I would not want to move the assembly out of the project directory, but this is the only solution I found.
I'm trying to test out some JNI code integrating a Java class with some ROS functionality and I'm struggling to get the Java methods linked up correctly. I've got the native code compiled against the JNI interface correctly (or so I think) but at runtime I get an UnsatisifiedLinkError on the first native method I have defined. At this point I'm not sure if the root cause is that the JVM isn't properly loading the .so file (in the same directory, and I've tried -Djava.library.path=.) or if it's successfully loading it and it's not finding the method correctly.
This error message gives so little to go on, is there a way to get more info about what exactly is causing it?
I'm not opposed to posting the source code if it would help, though I'd have to do some editing before I can upload it so I'll wait to see if you guys think it might be helpful.
Talker.java:
public class Talker {
/**
* ROS Native methods
*
* Simple passthrough to the C++ native methods in the ROS layer
*/
private static native void rosAdvertise();
private static native void rosPublish();
private static native void rosSpinOnce();
{
System.loadLibrary("ros-test-native-talker");
}
public static void main(String[] args) {
rosAdvertise();
while (true) {
rosPublish();
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
rosSpinOnce();
}
}
}
ros-test-native-talker.cpp:
#include "test_rostest_Talker.h"
#include "ros/ros.h"
#include "std_msgs/Time.h"
ros::Publisher outbound;
JNIEXPORT void JNICALL Java_test_rostest_Talker_rosAdvertise
(JNIEnv *, jclass) {
int argc = 0;
char **argv;
ros::init(argc, argv, "ros-native-timing-tester");
ros::NodeHandle n;
outbound = n.advertise<std_msgs::Time>("chatter", 1000);
}
JNIEXPORT void JNICALL Java_test_rostest_Talker_rosPublish
(JNIEnv *, jclass) {
ros::Time tx_timestamp = ros::Time::now();
ROS_INFO("Sending message at %d.%d", tx_timestamp.sec, tx_timestamp.nsec);
std_msgs::Time msg;
msg.data = tx_timestamp;
outbound.publish(msg);
}
JNIEXPORT void JNICALL Java_test_rostest_Talker_rosSpinOnce
(JNIEnv *, jclass) {
ros::spinOnce();
}
and the output:
rush#lubuntu64vm:~/javarostest$ java -Djava.library.path=. -cp ros-test-native-1.0-SNAPSHOT.jar test.rostest.Talker
Exception in thread "main" java.lang.UnsatisfiedLinkError: test.rostest.Talker.rosAdvertise()V
at test.rostest.Talker.rosAdvertise(Native Method)
at test.rostest.Talker.main(Talker.java:21)
I have no clue why but refactoring the above code slightly caused it to work. If I take the native methods out of the main classand put them in a separate class (thus removing the static modifier on the native methods) which is invoked by the main class, it all links and works fine. I'm not certain nor do I even have a clue why, but I think the static modifier on those methods was causing some issues.
I'm playing around with JNI on Windows 7x64, Java version is 1.7.0_40 and MinGW / GCC / G++ 4.7.2.
Trying to power off my monitor from Java. So, I've created a class:
public class MonitorTrigger {
static {
try {
System.load(new ClassPathResource("MonitorTrigger.dll").getFile().getAbsolutePath());
} catch (IOException e) {
e.printStackTrace();
}
}
public native void on();
public native void off();
}
Then, generated h file from it (with Eclipse, but I beleive it uses javah):
/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger */
#ifndef _Included_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger
#define _Included_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger
* Method: on
* Signature: ()V
*/
JNIEXPORT void
JNICALL Java_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger_on(
JNIEnv *, jobject);
/*
* Class: by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger
* Method: off
* Signature: ()V
*/
JNIEXPORT void
JNICALL Java_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger_off(
JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
And implemented it:
#include "by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger.h"
#include <iostream>
#include <windows.h>
JNIEXPORT void JNICALL Java_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger_on
(JNIEnv * env, jobject object) {
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) -1);
}
JNIEXPORT void JNICALL Java_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger_off
(JNIEnv * env, jobject object) {
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) 2);
}
It does not work! I get exception:
Exception in thread "main" java.lang.UnsatisfiedLinkError: by.dev.madhead.bubikopf.desktop.monitortrigger.util.MonitorTrigger.off()V
at by.dev.madhead.bubikopf.desktop.monitortrigger.util.MonitorTrigger.off(Native Method)
at by.dev.madhead.bubikopf.desktop.monitortrigger.App.main(App.java:7)
I was stuck for a bit, but after googling, I've found a solution - use __cdecl instead of __stdcall convention for exported function. So, I've made a very dirty hack:
#define JNICALL __cdecl
And it works!
It was previously defined as __stdcall at jni_md.h. I realize that I'm doing a very bad thing, which harm kittens, but I lack of experience in C/ C++, and I cannot figure out, why I should redefine this? Why standard header (jni_md.h) defines this incorrectly?
For 32 bit DLLs being used by jni, the code has to be compiled without the usual __stdcall adornments - i.e. the code can't have the #N postfix on the symbol name; but it still needs to be compiled in __stdcall mode.
When compiling the dll under mingw, you need to add the option --kill-at to the linker. This is generally passed using -Wl,--kill-at. This will cause the #N postfix to be removed, and so appear as a simple symbol which can be linked at run-time by the JVM. The option can be abbreviated to -Wl,-k as well.
An alternative is to use a map file, which exports the symbols in their unmangled form, which is the mechanism that's used most often when compiling with microsoft's own visual studio compiler.
This is pretty poorly documented, and the resulting error you get when it happens doesn't help too well.
I'd recommend looking at JNA, which makes writing native code wrappers a lot simpler, and in this case would mean no C++ code needed.
The JNA code to accomplish this looks like:
import com.sun.jna.platform.win32.User32;
import com.sun.jna.platform.win32.WinUser;
import com.sun.jna.platform.win32.WinDef.LPARAM;
import com.sun.jna.platform.win32.WinDef.WPARAM;
public class JNAMonitorTrigger {
public void monitor(LPARAM param) {
User32.INSTANCE.PostMessage(WinUser.HWND_BROADCAST,
WinUser.WM_SYSCOMMAND,
new WPARAM(0xf170), param);
}
public void on() {
monitor(new LPARAM(-1));
}
public void off() {
monitor(new LPARAM(2));
}
public static void main(String args[]) throws Exception {
JNAMonitorTrigger me = new JNAMonitorTrigger();
me.off();
Thread.sleep(1000);
me.on();
}
};
Even though you're on Windows, you're using GCC, which means this: Is there STDCALL in Linux? is still basically going to apply.
The functions in your file generated by java.h are declared as extern "C"
You have to add it in your cpp file :
extern "C"
JNIEXPORT void JNICALL Java_by_dev_madhead_bubikopf_desktop_monitortrigger_util_MonitorTrigger_on
(JNIEnv * env, jobject object) {
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) -1);
}
I'm making a simple JNI test app using Eclipse on Windows. My C++ compiler is MinGW 4.6.2. Java is throwing an UnsatisfiedLinkError when I try to invoke a function in my test DLL (the DLL itself loads without problem). I have verified that my DLL exports a "C" function with the same name as the function generated by the javah utility.
How could trying to invoke the function possibly generate a link error? (Also, is there any way to get more detail as to what symbol isn't being found? A bald statement that there's an UnsatisfiedLinkError is next to useless.)
Here's the Java which defines the native function:
package com.xyz.jsdi_test;
import java.io.File;
public class JSDI
{
public static native void func(
String str,
int i,
Integer ii,
long j /* 64 bits */,
Long jj,
byte[] b
);
public static void dummy()
{
System.out.println("JSDI.dummy()");
}
static
{
File f = new File("..\\jsdi\\bin\\jsdi.dll");
System.out.println("Preparing to load: " + f);
System.load(f.getAbsolutePath());
System.out.println("Successfully loaded: " + f);
}
Here is the corresponding output from javah:
...
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: com_xyz_jsdi_test_JSDI
* Method: func
* Signature: (Ljava/lang/String;ILjava/lang/Integer;JLjava/lang/Long;[B)V
*/
JNIEXPORT void JNICALL Java_com_xyz_jsdi_1test_JSDI_func
(JNIEnv *, jclass, jstring, jint, jobject, jlong, jobject, jbyteArray);
#ifdef __cplusplus
}
#endif
...And how I implemented the function...:
extern "C"
{
JNIEXPORT void JNICALL Java_com_xyz_jsdi_1test_JSDI_func(
JNIEnv * env,
jclass _class,
jstring str,
jint i,
jobject ii,
jlong j,
jobject jj,
jbyteArray b
)
{
// don't do anything...let's just try to get called successfully...
}
} // extern "C"
Here is how I attempt to invoke it.
...
public static void main(String[] args)
{
JSDI.dummy(); // cause class to load, which should cause System.load() to run.
JSDI.func("hello", 0, 0, 0L, 0L, (byte[])null);
}
Finally, this is the output:
Preparing to load: ..\jsdi\bin\jsdi.dll
Successfully loaded: ..\jsdi\bin\jsdi.dll
JSDI.dummy()
java.lang.UnsatisfiedLinkError: com.xyz.jsdi_test.JSDI.func(Ljava/lang/String;ILjava/lang/Integer;JLjava/lang/Long;[B)V
at com.xyz.jsdi_test.JSDI.func(Native Method)
at com.xyz.jsdi_test.SimpleTest.main(SimpleTest.java:24)
SOLVED IT -- WOOO!
It turns out that MSVC prepends an underscore to the name of __stdcall functions. MinGW does not. The Windows JVM apparently expects the '_' prefix. As soon as I prepended '_' to the function name and rebuilt with MinGW, everything worked just dandy.
eg:
JNIEXPORT void JNICALL Java_com_xyz_jsdi_1test_JSDI_func ==> _Java_com_xyz_jsdi_1test_JSDI_func
EDIT:
The --add-stdcall-underscore feature of the dlltool utility included with MinGW can solve this problem for you transparently. Set it up in your Makefile and you don't need to worry about having different versions of the actual source code for different compilers. See at this link.
Posting a working example, copy the content in the three files in the same directory (modify the path to your JDK) then invoke build.cmd
/* File: HelloWorld.java */
public class HelloWorld {
private static native void writeHelloWorldToStdout();
public static void main(String[] args) {
System.loadLibrary("HelloWorld");
writeHelloWorldToStdout();
}
}
/* File: HelloWorld.c */
#include <stdio.h>
#include "HelloWorld.h"
JNIEXPORT void JNICALL Java_HelloWorld_writeHelloWorldToStdout(JNIEnv *env, jclass c)
{
printf("Hello World!");
}
rem File: build.cmd
%echo off
echo delete generated binaries
del HelloWorld.class
del HelloWorld.dll
del HelloWorld.h
del HelloWorld.def
echo Compile the Java Class
javac HelloWorld.java
echo Generate the Header file
javah -classpath . -o HelloWorld.h HelloWorld
echo Build the DLL
gcc -I"C:\Program Files (x86)\Java\jdk1.7.0_25\include" -I"C:\Program Files (x86)\Java\jdk1.7.0_25\include\win32" -Wl,--add-stdcall-alias -Wl,--output-def,HelloWorld.def -shared -o HelloWorld.dll HelloWorld.c
echo run the program
java HelloWorld
The signature in the exception doesn't have the 'int' parameter. So your Java code disagrees with your native code.
We currently have some image processing software written in c++ which is being used by our IOS application. I am trying to integrate this image processing code into the android project that I created using the Android NDK.
I have my android project and the sdk all setup and ready to go. I also have the ndk setup and ready to go.
I was following through on this tutorial (which is awesome), and I got stumped at the part that he defined the code for native.c because it had a function name like this,
void Java_com_mamlambo_sample_ndk1_AndroidNDK1SampleActivity_helloLog(JNIEnv * env, jobject this, jstring logThis)
It almost looks to me like I have to go through all of my existing c++ functions and alter the code in order for the NDK to recognize it.
So here are my questions,
Do I have to alter my existing c++ code in order for it to work with the ndk builder? And if so, what are the things I need to change in my code for this work?
Is there a way to have the Android.mk file build an entire directory? I have a lot of files and I did not want to have to list out every single one of them in order to get them built.
1) You should be able to build without alteration, but you will need to write some of those JNI wrapper functions to call it from Java. Hopefully you have a small number of top-level classes and you will only need to wrap those. E.g. Here's what I have for a game I'm (slowly) writing:
// android.cpp
#include "game.h"
#include <jni.h>
namespace {
Game* toGame(jlong gamePtr) {
return reinterpret_cast<Game*>(gamePtr);
}
}
extern "C" {
jlong Java_com_rarepebble_game3_Game_create(JNIEnv* env, jobject jobj) {
Game* g = new Game();
return reinterpret_cast<jlong>(g);
}
void Java_com_rarepebble_game3_Game_destroy(JNIEnv* env, jobject jobj, jlong gamePtr) {
delete toGame(gamePtr);
}
void Java_com_rarepebble_game3_Game_update(JNIEnv* env, jobject jobj, jlong gamePtr, jboolean isTouching, jfloat touchX, jfloat touchY) {
toGame(gamePtr)->update(isTouching, touchX, touchY);
}
void Java_com_rarepebble_game3_Game_render(JNIEnv* env, jobject jobj, jlong gamePtr) {
toGame(gamePtr)->render();
}
// ... and a few others. Only one class, though.
}
On the Java side this lets me declare those functions in my com.rarepebble.game3.Game class and call them at the appropriate times in the app's lifecycle. (Note how the Java package, class and function names correspond to the function names in C++):
//Game.java
package com.rarepebble.game3;
// (imports)
public class Game {
static {
System.loadLibrary("game3lib");
}
// These are the functions you defined in C++
private native long create();
private native void destroy(long gamePtr);
private native void update(long gamePtr, boolean isTouched, float x, float y);
private native void render(long gamePtr);
private long gamePtr = 0;
Game() {
gamePtr = create();
}
#Override
protected void finalize() throws Throwable {
if (gamePtr != 0) {
destroy(gamePtr);
}
super.finalize();
}
// etc...
}
2) You can use
LOCAL_SRC_FILES := $(wildcard *.cpp) $(wildcard subdirectory/*.cpp) #etc...
Edit: As requested, my C++ Game class header, "game.h":
// game.h
#ifndef GAME_INCLUDED
#define GAME_INCLUDED
// Various game and standard library includes.
// *NO* JNI or Android includes.
namespace game {
class Game {
public:
Game();
~Game();
void update(bool isTouching, float touchX, float touchY);
void render();
// other funcs...
private:
// etc...
};
}
#endif //def GAME_INCLUDED
Similarly, "game.cpp" doesn't include any JNI stuff either.