Develop Reference

Using VC++ dll using JNA

I am using a BTICARD.DLL, which is the dll of Arinc429 card. I need to write wrapper class in Java for the functions like BTICard_CardOpen for example.
I Had written an interface below BTICardAPI.java:
package NLIPjt;
import com.sun.jna.win32.StdCallLibrary;
import com.sun.jna.Native;
// import com.sun.jna.ptr.IntByReference;
import com.sun.jna.Pointer;
public interface BTICardAPI extends StdCallLibrary {
BTICardAPI INSTANCE = (BTICardAPI) Native.loadLibrary("BTICARD", BTICardAPI.class);
int BTICard_CardOpen(Pointer LPHCARD, int cardnum);
}
and my Java implementation prog
BTICardTest.java:
package NLIPjt;
// import com.sun.jna.ptr.IntByReference;
import com.sun.jna.Pointer;
public class BTICardTest {
public static void main(String args[]) {
BTICardAPI BTI1 = BTICardAPI.INSTANCE;
int iErr;
int CardNo = 0;
Pointer CardHandle = null;
iErr = BTI1.BTICard_CardOpen(CardHandle, CardNo);
System.out.println("Error Value: " + iErr);
}
}
i get the following error in netbeans IDE:
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'BTICard_CardOpen': The specified procedure could not be found.
at com.sun.jna.Function.<init>(Function.java:245)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:566)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:542)
at com.sun.jna.NativeLibrary.getFunction(NativeLibrary.java:528)
at com.sun.jna.Library$Handler.invoke(Library.java:228)
at com.sun.proxy.$Proxy0.BTICard_CardOpen(Unknown Source)
at NLIPjt.BTICardTest.main(BTICardTest.java:14)
Looking for a solution!!

According to the documentation you need to make the library available. There are three ways to do this.
Make your target library available to your Java program. There are
several 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.
Make your native library available on your classpath, under the path
{OS}-{ARCH}/{LIBRARY}, where {OS}-{ARCH} is JNA's canonical prefix for
native libraries (e.g. win32-x86, linux-amd64, or darwin). If the
resource is within a jar file it will be automatically extracted when
loaded.

System.out.println() stops working after JNA/DLL call?

I have multiple System.out.println() calls in my program. My issue is that, after making a call to a DLL through a JNA Library (which does work without returning an error code or throwing an exception), subsequent calls to println() execute without printing anything! I know that the statements are executing because I'm stepping through them in NetBeans!
Unfortunately, I don't have a clue about the C code behind the DLL, and I guess you won't be able to duplicate this unless you register with qimaging.com and download the QCam SDK. I'm just wondering if anyone has experienced anything similar to this System.out.println() behavior, i.e. that it works until a certain point, then stops printing even though it executes.
This is my main test class:
package hwi.scope;
import com.sun.jna.ptr.IntByReference;
import hwi.scope.qcam.QCamDriverX64;
import java.io.File;
/**
* QCamTest class tests some functions of the QCam driver library.
* #author rnagel
*/
public class QCamTest
{
private static QCamDriverX64 driver;
// Main test method:
public static void main() throws Exception
{
// Set path to easily find DLL in the /dll folder:
File f = new File("dll");
System.setProperty("jna.library.path", f.getCanonicalPath());
// Use JNA to load the driver library:
driver = QCamDriverX64.INSTANCE;
// Load camera driver from the library:
loadQCamDriver();
// Print out the driver version:
printQCamVersion();
}
// Load camera driver method:
public static void loadQCamDriver()
{
System.out.println("Loading QCam driver..."); // Executes and prints to console
int error = driver.QCam_LoadDriver();
System.out.println("Done loading driver."); // Executes, but doesn't print to console
}
// Print camera driver version:
public static void printQCamVersion()
{
// Obtain driver version as a combination of 'major' and 'minor' increments:
IntByReference major = new IntByReference(), minor = new IntByReference();
int error = driver.QCam_Version(major, minor);
// At this point, I've verified that I have a obtained a valid version.
System.out.println("QCam v." + major.getValue() + "." + minor.getValue()); // Executes, but doesn't print to console
}
}
And this is the QCamDriverX64 class that I've made to wrap the DLL:
package hwi.scope.qcam;
import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.ptr.IntByReference;
/**
* QCamDriverX64 wraps the 64-bit version of the QCam driver DLL.
* #author rnagel
*/
public interface QCamDriverX64 extends Library {
// Make the library name publicly accessible:
public static final String DLL_NAME = "QCamDriverx64";
// Load an instance of the library using JNA:
public static final QCamDriverX64 INSTANCE = (QCamDriverX64) Native.loadLibrary(DLL_NAME, QCamDriverX64.class);
// Load the QCam driver:
int QCam_LoadDriver();
// Obtain QCam driver version # (in major and minor increments)
int QCam_Version (IntByReference major, IntByReference minor);
}
I'm using NetBeans 8.2 and JDK 1.8.0_121.
Thanks for taking a look! I'd appreciate any insight!

You can easily reproduce that by calling
System.out.close();
System.err.close();
I'm assuming that the native code in the DLL is doing something in that respect. It might be friendly by actually doing above call. In that case you could save System.out and System.err into variables, set some dummy streams with System.setOut() and System.setErr() and put everything back as it was before after the DLL-call. If the native code closes the underlying file handles, that won't help and the only option is to file a bug report at the provider of the DLL.

Check if tools.jar is available and load it dynamically during runtime

I'm working on a monitoring application, which uses Sigar for monitoring to monitor different kind of applications. One problem with Sigar is that when monitoring the heap usage of a Java application (JVM) I only get the maximum heap size but not the actually used heap size of the JVM.
So I extended my monitoring application to use JMX to connect to a JVM and retrieve the CPU as well as the heap usage. This works fine so far, but
I want to automise everything as much as possible and I don't want to start all my applications, being monitored, with JMX activated, but activate it dynamically when needed with the following piece of code:
private void connectToJVM(final String pid) throws IOException, AgentLoadException, AgentInitializationException {
List<VirtualMachineDescriptor> vms = VirtualMachine.list();
for (VirtualMachineDescriptor desc : vms) {
if (!desc.id().equals(pid)) {
continue;
}
VirtualMachine vm;
try {
vm = VirtualMachine.attach(desc);
} catch (AttachNotSupportedException e) {
continue;
}
Properties props = vm.getAgentProperties();
String connectorAddress = props.getProperty(CONNECTOR_ADDRESS);
if (connectorAddress == null) {
String agent = vm.getSystemProperties().getProperty("java.home") + File.separator + "lib"
+ File.separator + "management-agent.jar";
vm.loadAgent(agent);
// agent is started, get the connector address
connectorAddress = vm.getAgentProperties().getProperty(CONNECTOR_ADDRESS);
}
vm.detach();
JMXServiceURL url = new JMXServiceURL(connectorAddress);
this.jmxConnector = JMXConnectorFactory.connect(url);
}
}
This works fine so far but the problem is that I have now a dependency to the tools.jar from the JDK.
My question is now can I somehow check during runtime if the tools.jar is available in the JAVA_HOME path and load it when it is? Because if it isn't available I just want to do the normal monitoring with Sigar, but if it is available I want to use JMX for monitoring Java applications.
My project is a maven project and I'm using the maven-shade-plugin to create a executable jar with all dependencies in it.
Currently I'm using a dirty hack I found in the internet which uses reflection to add the tools.jar dynamically to the system classpath if it exists. But I'm wondering if it is possible to do it differently as well?
Thanks in advance for your support.

I do a similar thing in my project, look here.
The idea is to load your utility class by differrent ClassLoader which has tools.jar in path.
File javaHome = new File(System.getProperty("java.home"));
String toolsPath = javaHome.getName().equalsIgnoreCase("jre") ? "../lib/tools.jar" : "lib/tools.jar";
URL[] urls = new URL[] {
getClass().getProtectionDomain().getCodeSource().getLocation(),
new File(javaHome, toolsPath).getCanonicalFile().toURI().toURL(),
};
URLClassLoader loader = new URLClassLoader(urls, null);
Class<?> utilityClass = loader.loadClass("some.package.MyUtilityClass");
utilityClass.getMethod("connect").invoke(null);

Finding tools.jar on the filesystem is a little more tricky than #apangin's solution.
Different JDK's stick the tools.jar in different places as shown by this method, which claims to support the IBM JDK and HotSpot on Mac.
But even the code I've referenced looks out of date. It suggests all mac JDK's use classes.jar, but my Mac 1.7 and 1.8 JDK's instead use tools.jar.
This other answer of mine shows locations of tools.jar and classes.jar files for mac some 1.6, 1.7 and 1.8 JDKs.

The code I ended up using is from: org.gridkit.lab::jvm Attach Api
https://mvnrepository.com/artifact/org.gridkit.lab/jvm-attach-api/1.2
Source code: http://central.maven.org/maven2/org/gridkit/lab/jvm-attach-api/1.2/
From that source code, you simply need one file: AttachAPI.java
/**
* Copyright 2013 Alexey Ragozin
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.gridkit.lab.jvm.attach;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
/**
* #author Alexey Ragozin (alexey.ragozin#gmail.com)
*/
class AttachAPI {
private static final LogStream LOG_ERROR = LogStream.error();
private static boolean started;
static {
try {
String javaHome = System.getProperty("java.home");
String toolsJarURL = "file:" + javaHome + "/../lib/tools.jar";
// Make addURL public
Method method = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
method.setAccessible(true);
URLClassLoader sysloader = (URLClassLoader)ClassLoader.getSystemClassLoader();
if (sysloader.getResourceAsStream("/com/sun/tools/attach/VirtualMachine.class") == null) {
method.invoke(sysloader, (Object) new URL(toolsJarURL));
Thread.currentThread().getContextClassLoader().loadClass("com.sun.tools.attach.VirtualMachine");
Thread.currentThread().getContextClassLoader().loadClass("com.sun.tools.attach.AttachNotSupportedException");
}
} catch (Exception e) {
LOG_ERROR.log("Java home points to " + System.getProperty("java.home") + " make sure it is not a JRE path");
LOG_ERROR.log("Failed to add tools.jar to classpath", e);
}
started = true;
};
public static void ensureToolsJar() {
if (!started) {
LOG_ERROR.log("Attach API not initialized");
}
}
}
To use this class, put it somewhere in your project and ensure you change its package accordingly. In the example below, I have placed the file in the same folder as my MyApp.java file but I've not amended the AttachAPI.java file's package statement to reflect that since I wanted to leave it pristine.
Lastly, in your main class, ensure you have a block such as the follows:
public class MyApp
{
static {
AttachAPI.ensureToolsJar();
}
public static void ensureToolsJar() {
// do nothing, just ensure call to static initializer
}
}
...
Now you will no longer need to specify a path to the tools.jar on the command line and can launch you app with simply a java -jar MyApp.jar

ClassNotFoundException using Processing's PApplet with Arduino Tool

I developer a basic Processing PApplet to run as a Tool in the Arduino IDE and that ran fine until Arduino 1.5.8. The problem I have is that in Arduino 1.6.0 some of the code got refactored and this happened on the Arduino side:
" In order to provide a better command line, IDE has been refactored
into app and arduino-core which is the old core In order to avoid
conflicts between classes, PApplet was moved from
processing.core.PApplet to processing.app.legacy.PApplet "
This explanation came from one of the Arduino IDE developers. It's worth noting that processing.app.legacy.PApplet is a (very)stripped down version of PApplet, discarding all graphics capabilities which I need.
Initially I was getting this error:
Uncaught exception in main method: java.lang.NoClassDefFoundError: processing/core/PApplet
Placing Processing's core.jar in the same location as the eclipse exported tool jar fixed this issues, but let to another:
Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: You need to use "Import Library" to add processing.core.PGraphicsJava2D to your sketch.
at processing.core.PApplet.makeGraphics(Unknown Source)
at processing.core.PApplet.init(Unknown Source)
The part that is confusing is I've used Processing's library source java files instead of the core.jar compiled library to avoid this issue, but it didn't change anything.
I've gone through PApplet's source code and found the graphics/renderer class gets loaded and instantiated at runtime here like so:
Class<?> rendererClass =
Thread.currentThread().getContextClassLoader().loadClass(renderer);
Constructor<?> constructor = rendererClass.getConstructor(new Class[] { });
PGraphics pg = (PGraphics) constructor.newInstance();
and this is where the ClassNotFoundException is caught throwing the Runtime exception:
catch (ClassNotFoundException cnfe) {
// if (cnfe.getMessage().indexOf("processing.opengl.PGraphicsOpenGL") != -1) {
// throw new RuntimeException(openglError +
// " (The library .jar file is missing.)");
// } else {
if (external) {
throw new RuntimeException("You need to use \"Import Library\" " +
"to add " + renderer + " to your sketch.");
} else {
throw new RuntimeException("The " + renderer +
" renderer is not in the class path.");
}
}
I'm getting more comfortable with java, but I don't have enough experience to figure this one out. It looks like a classpath issue, but I'm not sure why this happens and how I should tell java where to find the classes it needs to load.
Here is the code test I'm using based on the Arduino Tool sample that comes with the IDE. Currently I'm exporting the jar file (not runnable) from eclipse:
/*
Part of the Processing project - http://processing.org
Copyright (c) 2008 Ben Fry and Casey Reas
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package com.transformers.supermangletron;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import processing.core.PApplet;
import processing.app.Editor;
import processing.app.tools.Tool;
//import processing.app.legacy.PApplet;
/**
* Example Tools menu entry.
*/
public class Mangler implements Tool {
private Editor editor;
public void init(Editor editor) {
this.editor = editor;
}
private void setupSketch(){
int w = 255;
int h = 255;
// PApplet ui = new PApplet();
TestApp ui = new TestApp();
JFrame window = new JFrame(getMenuTitle());
window.setPreferredSize(new Dimension(w,h+20));
window.add(ui);
window.invalidate();
window.pack();
window.setVisible(true);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
ui.init();
System.out.println("setup complete");
}
public String getMenuTitle() {
return "Mangle Selection";
}
public void run() {
setupSketch();
}
}
and here's the basic test Applet I'm trying to display:
package com.transformers.supermangletron;
import processing.core.PApplet;
public class TestApp extends PApplet {
public void setup(){
size(100,100);
}
public void draw(){
background((1.0f+sin(frameCount * .01f)) * 127);
}
}
How can I fix this ClassNotFoundException with my setup?
Any hints on what I should double check regarding class paths?

If you're getting this error when you run from eclipse, you have to add the library jars to your classpath. You do this by right-clicking your project, going to properties, then to Java Build Path. Make sure the library jars are listed under the Libraries tab.
If you're getting this error when you run an exported jar, then you need to do one of two things:
Either make sure you export a runnable jar with the library jars embedded inside the main jar. Do this from eclipse by right-clicking the project, going to Export, then choosing "runnable jar" from the list.
Or, make sure you set the classpath as a JVM argument. You do this using the -cp option from the command line.

Sigar UnsatisfiedLinkError

I'm new to Sigar. I would like to run a simple test to know how I can monitor my system.
I added sigar-1.6.4 and log4j as external libraries, but when I go to run it, I face this error:
Exception in thread "main" java.lang.UnsatisfiedLinkError: org.hyperic.sigar.Sigar.getCpuInfoList()[Lorg/hyperic/sigar/CpuInfo;
at org.hyperic.sigar.Sigar.getCpuInfoList(Native Method)
Here is my code:
import java.util.Map;
import org.hyperic.sigar.CpuInfo;
import org.hyperic.sigar.FileSystem;
import org.hyperic.sigar.Sigar;
import org.hyperic.sigar.SigarException;
public class Test {
/**
* #param args
*/
public static void main(String[] args) {
Sigar sigar = new Sigar();
CpuInfo[] cpuinfo = null;
try {
cpuinfo = sigar.getCpuInfoList();
} catch (SigarException se) {
se.printStackTrace();
}
System.out.println("---------------------");
System.out.println("Sigar found " + cpuinfo.length + " CPU(s)!");
System.out.println("---------------------");
}
}
Any help would be appreciated.

I understood the problem!
I have to use the following JVM Argument:
-Djava.library.path="./lib"
in Run Configuration, Arguments tab, VM arguments in eclipse, while the contnet of sigar-bin/lib is in lib folder.

Sigar works via JNI. As such, the appropriate .so or .dll file needs to be in the path specified by the java.library.path property.
Check your sigar distribution - the zip file, I mean. Unzip it and copy the contents of
sigar-bin\lib to a location accessible by your Path, PATH, and LD_LIBRARY_PATH environment variables. Usually, only one file needs to be accessible per platform.
That should do the trick, if it doesn't, let me know and I'll see what I can do.