Develop Reference

Ecplise Java JNI, java.lang.UnsatisfiedLinkError loading dll

I'm having a problem with loading printer dll. I have a dll file from the printer manufacturer (JniPrinterStatusLib.dll). I wrote code like printer manufacturer suggested. The code is:
package com.printer.test
public class JniPrinterStatus {
static{
System.loadLibrary("JniPrinterStatusLib");
}
public native int GetStatus(String printer);
}
package com.printer.test
public class TestSample {
public static void main(String[] args) {
int status;
String printer = "MY PRINTER";
JniPrinterStatus jps = new JniPrinterStatus();
System.out.println("PRINTER NAME = " + printer);
status = jps.GetStatus(printer);
if (status == -1) {
System.out.println("status = -1");
}
else if (status == 0) {
System.out.println("status = NORMAL");
}
else if ((status & 0x00000080) != 0) {
System.out.println("status = PRINTER_STATUS_OFFLINE");
}
else if ((status & 0x00400000) != 0) {
System.out.println("status = PRINTER_STATUS_DOOR_OPEN");
}
else if ((status & 0x00000010) != 0) {
System.out.println("status = PRINTER_STATUS_PAPER_OUT");
}
else if ((status & 0x00000800) != 0) {
System.out.println("status = PRINTER_STATUS_OUTPUT_BIN_FULL");
}
else if ((status & 0x00000040) != 0) {
System.out.println("status = PRINTER_STATUS_PAPER_PROBLEM");
}
}
}
I used Eclipse to run the code, i put the dll library in the folder project and the error is
PRINTER NAME = MY PRINTER
Exception in thread "main" java.lang.UnsatisfiedLinkError: com.printer.test.JniPrinterStatus.GetStatus(Ljava/lang/String;)I
at com.printer.test.JniPrinterStatus.GetStatus(Native Method)
at com.printer.test.TestSample.main(TestSample.java:10)
If i move the source from the package "com.printer.test" to default package the code works and show:
PRINTER NAME = MY PRINTER
status = -1
I don't know how it's possible. If i compile and run the code from command prompt without package it works.
Where is the problem?
Thank you

From the javadoc for class UnsatisfiedLinkError...
Thrown if the Java Virtual Machine cannot find an appropriate
native-language definition of a method declared native.
That means that function Java_com_printer_test_JniPrinterStatus_GetStatus is not found.
Method loadLibrary in class java.lang.System usually searches the directories listed in the [System] property "java.library.path". For Windows machines, the value of this property is generally the value of the PATH environment variable.
So I suggest printing out the value of that property in your code to see whether it includes the directory containing your DLL. If it doesn't then you need to fix that, either by relocating the DLL or changing the PATH environment variable or launching your java program with the -Djava.library.path=... option. After that you need to check the signature of the native method. Dependency Walker is a tool I use at my work to accomplish this.
EDIT
Having re-read your question, I feel I did not accurately address your question, so let me add...
The default behaviour of Eclipse is to copy resource files, like DLLs, to the output folder. So if you put your DLL in folder src\com\printer\test, it will get copie to folder bin\com\printer\test. My guess is that the current, working directory, i.e. . is in your "java.library.path" which is why it works when your java code is in the default package.

Sorry, actually I wanted to write a comment, but as I'm still low on reputation, I have to try and guess an answer.
There should be no need to recompile the dll - it's just some native code to be invoked.
The java package of the class loading the dll should not make a difference, either.
You have to take care about your system architecture: A 64-bit dll file will fail in a 32-bit JRE and vice versa. Make sure, your JRE architecture matches the dll architecture.
Another thing to take into account is your working directory. Eclipse may use a working directory different from what you used when you ran you program from console.
Last but not least, please have a look at your java.library.path variable.
This page might also help: https://www.chilkatsoft.com/java-loadLibrary-Windows.asp
I covers all the details.

The expected package of the Java classes is hard-coded in the JNI library. In your case, it's the default package.
Let me expand on that. When one implements a native method in a JNI library, one has to create a public C function with a name in the following format:
Java_com_mypackage_MyClass_MyMethod
In other words, the JNI library can't provide methods for the classes in arbitrary packages - only for classes in packages that the JNI library authors had in mind.
In your case, it's the default one. The C function goes Java_JniPrinterStatus_GetStatus. If you call your class MyPrinterStatus, or place it into package com.foobar, the JNI run-time won't be able to associate the C function with the declared Java native method. That's just how JNI was designed.

How to get static final variables using JNA

I am using the GLEW library glew32.dll (standard download from the GLEW website) and I am trying to load the variable GLEW_OK. This variable is defined in the glew.h file (as a uint of 0), so I am assuming it would be included in the glew32.dll file. However, when I use the Java JNA code :
NativeLibrary glew = NativeLibrary.getInstance("glew.dll");
Pointer p = glew.getGlobalVariableAddress("GLEW_OK");
System.out.println(p.getInt(0));
I am given an error of Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up 'GLEW_OK': The specified procedure could not be found.
at com.sun.jna.NativeLibrary.getGlobalVariableAddress(NativeLibrary.java:587)
at mcclean.opengl.glew.GLEWUtils.init(GLEWUtils.java:22)
The library is loaded fine, but it appears the static variable could not be found. Why is the static variable not being loaded?

Looking at the header file glew.h, GLEW_OK is found as such:
/* error codes */
#define GLEW_OK 0
This is a preprocessor definition. This is not a "static final variable" as you would conceive in the Java world. When a C++ project is compiled, preprocessor #defines are essentially "copypasted" by the preprocessor into the code. This means that if (val == GLEW_OK) is literally changed into if (val == 0).
Since the preprocessor simply replaces the text, there is no information about the names or the origins of the values originating from defines in the .dll file.
You need to manually find the values. You can do this by downloading the binaries from GLEW and navigating to the include/GL/glew.h file. After this, you could create a class for the constants in Java:
class GlewConstants {
public static final int GLEW_OK = 0;
// ...
}

Getting java.lang.UnsatisfiedLinkError at runtime

I'm trying to use JNI to access C++ methods from a Java class. I'm able to compile (both in Eclipse or on command line) my Java class fine, but on executing the class at runtime, I'm getting:
Exception in thread "main" java.lang.UnsatisfiedLinkError: com.domain.services.CallServiceAPIS.createSession()I
at com.domain.services.CallServiceAPIS.createSession(Native Method)
at com.domain.services.CallServiceAPIS.main(CallServiceAPIS.java:18)
Java code is as follows:
package com.domain.services;
public class CallServiceAPIS {
static {
System.loadLibrary("service.client");
}
public native int createSession();
public static void main(String[] args) {
System.out.println(System.getProperty("java.library.path"));
new CallServiceAPIS().createSession();
}
}
I included the printout of the java.library.path just to make sure it's pointing to the correct location of the C++ library - and it is. I also tried setting the LD_LIBRARY_PATH in my Eclipse environment. But neither worked.
Note that the System.loadLibrary call IS working since 1) the code compiles and 2) the error occurs on line 18, which is the new CallServiceAPIs call.
C++ code:
int createSession(const PosServiceInfo info, const SessionArgs& args, Domain::UUID& uuidSession)
{
return int::undefined;
}
Any ideas?

Never mind. I realized that I was using the JNI interface incorrectly. I was thinking you could load an EXISTING C++ library using EXISTING C++ source. But you basically have to rewrite the existing code to make use of the JNI interface.

Unsure about reason behind NoClassDefFoundError

I have built a DLL which I am attempting to wrap Java code with, however I am having some troubles with running my Java program. I wrote a simple test DLL and Java program and am producing the same error, and although there are plenty of resources regarding NoClassDefFoundError online I can't seem to solve mine with any troubleshooting methods.
Here is my D:\Test1.Java file
public class Test1 {
static {
//System.loadLibrary("HeyLand");
System.load("D://HeyLand.dll");
}
public native void displayHeyLand();
public static void main (String[] args) {
Test1 t = new Test1();
t.displayHeyLand();
}
}
After compiling, attempting to run D:\Test1.classresults in the following:
D:\>java Test1.class
Exception in thread "main" java.lang.NoClassDefFoundError: Test1.class
Caused by: java.lang.ClassNotFoundException: Test1.class
at java.net.URLClassLoader.findClass(URLClassLoader.java:434)
at java.lang.ClassLoader.loadClass(ClassLoader.java:660)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:358)
at java.lang.ClassLoader.loadClass(ClassLoader.java:626)
Could not find the main class: Test1.class. Program will exit.
Why I am stumped :
1. I have set my classpath to be D:\, so I believe my class definition would be in the classpath, and I do not see how my compile-time and run-time classpaths could be any different.
2. I don't see how this could have anything to do with static initialization, and I believe the exception would look different.
Perhaps I'm just missing something incredibly simple, I am very newbie with Java.
Any help is greatly appreciated!

The classpath environmental variable is taking precedence over that in the java run command. You need to specify the class location (as well as removing the .class file extension)
java -cp . Test1

Java normal syntax for executing class file is
Java [<options>....} <class-name> [<arguments>....]
For example
java com.package.name.Test1
here how compiler works
1. Compiler search for complete class name
2. Load that class
3. check for main method - in the same class
4. Call main method with passed arguments in command line string.
Now following are the possibilities why your class may not found main method.
1 - forgot to include package name
I am new developer in java but I found when I run application using eclips or intellJ editor it gives different path and package name and execute code as I noticed it on command line edior. So make sure you are including package name
For example:
java com.package.name.Test1 instead of
java Test1
2. File name or pathname rather then class name
As I noticed output file is in different location. That why class file path was different.
java Test1.class
java com/package/name/Test1.class
3. Typo
also I noticed you are using
static {
//System.loadLibrary("HeyLand");
System.load("D://HeyLand.dll");
}
Is this function ? or constructor? If it is function then where is name of the function? You cant write code without any reference in classs

JNA to call a DLL without source code from java

I have to call a dll method and I don't have the source code from dll, I was reading about JNI and understood that you should have the source to input the JNI library in the code (.h).
My second shoot is JNA, but I am getting the same error, although you don't have to change anything in DLL.
I created two classes to test:
interface:
package icom;
import com.sun.jna.Library;
public interface IConectorT extends Library {
int StartConector(byte[] conectorStatus, String icomPath);
}
DLL method call:
package icom;
import com.sun.jna.Native;
public class ConectorTJna {
public static void main(String args[]) {
IConectorT lib = (IConectorT) Native.loadLibrary("ConectorT", IConectorT.class);
int teste = lib.StartConector(null, "C:\\ICOM");
System.out.println("RESULT: " + teste);
}
}
When I call the lib.StartConector method I get this:
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error
looking up function 'StartConector': The specified procedure could not
be found. at com.sun.jna.Function.(Function.java:179) at
com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:350) at
com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:330) at
com.sun.jna.Library$Handler.invoke(Library.java:203) at
$Proxy0.StartConector(Unknown Source) at
icom.ConectorTJna.main(ConectorTJna.java:10)

Did you specify path to the library, e.g. using system property?
Here are the details from "Getting Started with JNA" guide:
Make your target library available to your Java program. There are two
ways to do this:
The preferred method is to set the jna.library.path system property to
the path to your target library. This property is similar to
java.library.path, but only applies to libraries loaded by JNA.
Change the appropriate library access environment variable before launching
the VM. This is PATH on Windows, LD_LIBRARY_PATH on Linux, and
DYLD_LIBRARY_PATH on OSX.
Taken from: https://github.com/twall/jna/blob/master/www/GettingStarted.md