Using JNI in applets: impossible due to classloader limitations?

Hello,
I attempted to post this question on java.net but no one seemed to know the answer. I am especially hoping that the Engineers who work on the Java Plugin will comment on this question. Thank you.
http://forums.java.net/jive/thread.jspa?messageID=248215
Gili

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I am using trying to use JNI to call a Java class from C++. The Java class uses JMS to send messages to a JMS message queue. At first I coded the C++ in a console application that created the JavaVM and used JNI to access the Java class. All worked fine. Then I called the Java class using JNI from threads and ran into the problem of the Java class not able to locate the JMS related classes. This was solved by placing the following line in the constructor of the Java class.
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How to use JNI?

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There really isn't a lot to using JNI.
There are examples on Sun's website:
http://developer.java.sun.com/developer/onlineTraining/Programming/JDCBook/jniexamp.html
There is also a little more simple example at:
http://www.inonit.com/cygwin/jni/helloWorld/java.html
Basically, here are the steps:
1) Create a simple java applet that will call your C/C++ code.
For practise, I would just use the HelloWorld example from www.inonit.com:
package example.jni;
public class HelloWorld {
     private static native void writeHelloWorldToStdout();
     public static void main(String[] args) {
          writeHelloWorldToStdout();
2) Name the file with the code above HelloWorld.java and compile it:
javac HelloWorld.java
3) Use javah to generate the C header file:
javah example.jni.HelloWorld
(You may need to cd to the parent directory of 'example', in this case)
4) The above line should create a example_jni_HelloWorld.h header file.
Use this header file in your C/C++ DLL. Make sure your C/C++ compile knows where to find jni.h. In my compiler, I added the following paths:
C:\J2SDK1.4.1\INCLUDE\
C:\J2SDK1.4.1\INCLUDE\WIN32
5) The trickiest part about JNI is passing in and returning parameters.
If you don't have to pass in or return any parameters, then you're almost done. Replace your C/C++ function protocol with the protocol in the header file you generated. Compile your DLL.
6) Copy the DLL to a path that it will be found by your Java Applet. (If running on Windows, this would be your System32 or System directory.)
7) I also had to edit my Path environment variable to include the Java Runtime bin directory. On my machine it was: C:\J2SDK1.4.1\jre\bin
8) Try running your java applet:
Java example.jni.HelloWorld
Good Luck!

Memory Allocation problem when using JNI

For a Project we need to interface Labwindows-CVI/ Teststand with an application written in Java. we are using JNI. The code uses JNI_CreateJavaVM to start a JVM to run the Java interface code. The code did run for some time , but now ( without any obvious change nor on the CVI side neither on the Java side) JNI_CreateJavaVM fails with -4 error code, that means that the start of the JVM failed due to memory allocation failure. First investigation showed, that even if Windows Task Manager shows about 600M free physical memory, you can allocate in CVI only about 250M as a single block at the time we are calling JNI_CreateJavaVM. That might be a little bit to less as we need to pass -Xmx192m to the JVM to run our code. Unfortunately just increasing the physical memory of that machine from 1.5G to 2G doesn't change anything. The free memory showed by Task Manager increases, but the allocatable memory block size does not. Are the any trick to optimize CVI/Teststand for that use case ? Or maybe known problems with JNI ?
Solved!
Go to Solution.

hi,
have you tried other functions to allocate memory?
the -Xmx command only sets the maximum heap size. You can try to use -Xms. This command sets the initial Java heap size.

How can I use JNI in JDeveloper???

hi
I have a native mathod,it can work very well use JCreator or JDK's Java command.
But it can't work in Jdeveloper with the errors :
java.lang.UnsatisfiedLinkError: no JniConvert in java.library.path
void java.lang.ClassLoader.loadLibrary(java.lang.Class, java.lang.String, boolean)
void java.lang.Runtime.loadLibrary0(java.lang.Class, java.lang.String)
void java.lang.System.loadLibrary(java.lang.String)
void myInterMediaPackage.ArithmaticBean.<clinit>()
void DrawTest.init()
void DrawTest.main(java.lang.String[])
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Dennis ,
Thank you very much.
I have resolved that question according to your second option.
thank you again!
Good luck.
2 options, that I know of (windoze, right?):
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If you deploy it to a jar, and put the DLL in there, I'd think it would see it - but I haven't gotten THERE, yet! :-P
Later.
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I have paid for ipages 09 on 15/05 but never succed to enter the serial code. After 45 days, altough I was charged by 20 chf, I cannot completely use all ipages tools(impossible to save ). How can I get again the serial code I paid for?

i have paid for ipages 09 on 15/05 but never succed to enter the serial code. After 45 days, altough I was charged by 20 chf, I cannot completely use all ipages tools(impossible to save ). How can I get again the serial code I paid for?

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Apple's support article on the subject says it's due to having a copy of the trial that is a higher version that the one you've purchased, but I'm not sure that is very common. This problem started with Snow Leopard & it seems to be some code in the iWork installers that doesn't do what it should.

I have problem when use 'JNI'

Hello every body,
I have an application language "C", which, I must make a wrapper java.
To do this using "JNI".
First I try to understand the functioning of JNI, I try it for the first example helloWorld.
all steps works well, and dynamic library was well create: libHelloWorld.so
The execution, it does'nt work
When I try to java Helloworld, here's what I see:
Exception in thread "main" java.lang.UnsatisfiedLinkError: /home/java/jniexamples/HelloWorld/libHelloWorld.so: Can't load IA 32-bit .so on a IA 32-bit platform
at java.lang.ClassLoader$NativeLibrary.load(Native Method)
at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1751)
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1676)
at java.lang.Runtime.loadLibrary0(Runtime.java:822)
at java.lang.System.loadLibrary(System.java:993)
at HelloWorld.<clinit>(HelloWorld.java:7)
Although I added the link to my library like this:
export LD_LIBRARY_PATH = $ LD_LIBRARY_PATH: / home / Install / java / jniexamples / HelloWorld
I dont understand where is the problem may be in the version I use of java, I use jdk-1.5.0-13?
Thank you in advance for your help
Regards
Daniel

Exception in thread "main" java.lang.UnsatisfiedLinkError: /home/java/jniexamples/HelloWorld/libHelloWorld.so: Can't load IA 32-bit .so As a guess that would suggest that it found a file (thus the name is correct) but that the contents do not represent a shared library that the VM will load.
That is usually because the compile/link options are wrong for the target VM.

Guidelines for when to use JNI

I didn't find an answer to this in any FAQ or the 2 JNI books I have, so apologies in advance if this is a common question whose answer has already been posted -
Do any guidelines exist for when, and to what extent, JNI should be used?
I'm currently working on my second project where the question of whether or not to use it has come up. Both projects were distributed and contained both C++ and Java code in different areas. The issue came up when the need arose to implement a new shared library that had to be used by both C++ and Java code. Logging and configuration services are examples of the new functionality.
The choice is whether to implement the new libraries primarily in C++ and supply a Java interface, via JNI, for Java code which needs to use it, or to implement the new libraries in both C++ and Java to support both types of clients.
On the previous project, a team member had extensive JNI experience and recommended the dual language implementation approach instead of JNI. This worked out ok except we did have to have to ensure the new library developer was skilled in both C++ and Java, and he had to be sure to update both when changes to 1 were necessary - a maintenance problem. The experienced JNI developer made this recommendation due to issues he had encountered previously - most notably issues related to errors in the native code which brought down the JVM.
On the current project, we're opting for base C++ implementations with JNI wrappers. That's making me somewhat nervous since the alternative seems safer.
What do other developers think?

Have you checked out www.javaworld.com. They usually have very good and in-depth articles. IMHO, it all depends on the sort of use your library is intended for. If its used extensively by native code, use C++ with a Java wrapper. It its the other way around, implement it in Java and use a JNI interface for native code. I would really consider this carefully before implementing stuff in C++ that is used from Java. First of all, Java is after all much simpler than C++, its a more elgant OO-language and you have the platform neutrality. On the other hand, C++ has its sides. I dont use JNI unless its absolutely neccessary, in situations like using legacy code.
These are just a few of my thoughts, hope it gives you some hints.

How to implement button installer using JNI or any native code

Hello All,
I am trying to implement installer that install button on internet explorer using JNI or native code so i am new to this technology .please suggest some approach.
Thanks All

Why would you ever do that?
There are a host of languages that will do that and many scripting. You can easily write Applets and services in Java that will work in IE, but to just add a button... just doesn't make sense.

JNI with applet

hello
I want to use JNI with the applet ,could any one give me helloworld applet using JNI
Thank you

hello
I want to use JNI with the applet ,could any one give
me helloworld applet using JNI
Thank youhttp://java.sun.com/sfaq/index.html#prevent

How to invoke a window using JNI?

Hello,
I need to invoke a C++ DLL from a Java Applet using JNI. The DLL should display an image in a separate window. Further I should be able to set the position of the DLL window, and should be able to minimize, maximize the DLL window from the Applet.
Well I am fairly new to C++. Any suggestions regarding how I should proceed?
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Hi jschell,
Thanks for the reply.
But I am sorry that I am not sure whether I understood your point. What I understood is I make an exe that displays the image and run it from Java like SHELL function in VB. In that case can I specify a particular image to be loaded from the applet? The applet and exe needs to be constant touch as the location , size etc of the window displaying the image could be controlled by the applet.
I have created a DLL which displays the specified the image in a modeless dialog box. I have succeded in invoking the DLL from applet. But the dll window hangs as soon as it loads! I got a suggestion to implement the display of modeless dialog box inside thread. Now I am investigating how to implement thread :) Please send in your advice if you have any?
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After enabling cellular data, i am receiving mails even if disable "use cellular data for mail", due to this data usage usage use is more, if we have fix please let me know

Phone Model and OS
Model - iphone 5
IOS 8.0.2
Problem Description
After enabling cellular data, i am receiving mails even if we disable "use cellular data for mail", due to this data usage usage use is more, if we have fix please let me know.
Steps:
1. Enable Cellular Data
2. Disable mail on "use cellular data for mail
3. check whether mail is received or not
tried multiple times and i am getting more billing amount because of data usage

Mail isn't the only app using data. Turning it off there has no effect whatsoever on whether the rest of iOS or other apps you have installed. In fact most apps use data these days, at a minimum for Notifications and often for gameplay and other features.

How can i call a VB6 project from my java application using JNI

hi
can anyone tell me the procedure of calling a VB6 project from any java application using JNI
if anyone does know then tell me the detail procedure of doing that. I know that i have to create a dll of that VB6 project then to call it from the java application.
if anyone know that procedure of creating dll file of an existing VB6 project please reply
please if anyone know then let me know

Ahh, kind of a duplicate thread:
http://forums.java.sun.com/thread.jspa?threadID=631642
@OP. You could have clarified your original post and the relationship of your question to java. You did not need a new thread.
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Using JNI in applets: impossible due to classloader limitations?

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