I followed the instructions from this video https://www.codenameone.com/how-do-i---access-native-device-functionality-invoke-native-interfaces.html, but my code is throwing java.lang.ClassNotFoundException: interfaces.MyNativeImpl on the look up line. The code I'm using is almost exactly that of the video.
package interfaces;
import com.codename1.system.NativeInterface;
public interface MyNative extends NativeInterface{
public String sayHi();
}
in the android native directory
package interfaces;
public class MyNativeImpl {
public String sayHi() {
return "hi";
}
public boolean isSupported() {
return true;
}
}
and in the java code:
MyNative my = (MyNative)NativeLookup.create(MyNative.class);
if(my != null && my.isSupported()){
System.out.println("Hello!");
}
Where did I go wrong now?
That is perfectly fine code and will work on the device.
You are seeing the exception in the simulator because the native/internal_tmp directory is missing from your runtime classpath but it shouldn't cause a problem other than no native interfaces on the desktop:
Related
It seems this problem is pretty common in java, but what I've tried isn't working and I might need some guidance. I also tried running the same code on another machine and I didn't run into this issue.
My class Node.java uses NodeInterface.java but when running Node.java I get the error: java.lang.ClassNotFoundException: NodeInterface.
So far I've made sure that everything is compiled, and I've used the command java -cp /home/ryan/Desktop/P2P NodeInterface but this produced the error Error: Main method not found in class NodeInterface. Which confuses me because I didn't think interfaces are supposed to have main methods.
I'm not sure if this will be helpful, but the environment file located in etc has PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin". I'm running ubuntu 18.04.5 LTS and using vscode with the java extension pack. My file structure in vs code
Please let me know if I'm missing any information that could make this problem easier to solve.
Edit: here is a more simplified version of the code. However, I don't think the problem lies in the code and instead has something to do with the classpath.
Node.java:
import java.net.InetAddress;
import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class Node implements NodeInterface {
private String URL;
public Node(String URL) throws RemoteException {
try {
this.URL = URL;
}
catch(Exception e) {
System.out.println(String.format("Encountering issues while constructing the server class. Error %s%n", e.getMessage()));
}
}
public static void main(String[] args) {
try {
Node node = new Node(args[0]);
System.out.println(InetAddress.getLocalHost().getHostName());
System.setProperty("java.rmi.server.hostname", InetAddress.getLocalHost().getHostName());
NodeInterface serverStub = (NodeInterface) UnicastRemoteObject.exportObject(node, 0);
Naming.bind(args[0], serverStub);
}
catch(Exception e) {
System.out.println(e.getMessage());
}
}
}
NodeInterface.java
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface NodeInterface extends Remote {
}
I want to wrap a C++ library (PCL) in Java code using JNI, but I am having inconsistent results. I have first created a PointXYZ class for testing and it looks like this:
package pcl;
public class PointXYZ extends NativeObject {
PointXYZ() { }
#Override
public native void alloc(); // creates pointer + handle on the native side
#Override
public native void dispose(); // sets handle to 0 and deletes pointer
public native float getX();
// ...
}
I have generated the C header for this class using javah, compiled everything using CMake, tested it using its getters and setters and everything works perfectly.
static {
System.setProperty("java.library.path", System.getProperty("user.dir") + "/lib");
System.loadLibrary("pcl_java_common");
}
#Test
void attributeAccessTest() {
PointXYZ p = new PointXYZ();
p.alloc();
p.setX(3);
assertEquals(p.getX(), 3);
p.dispose();
// all is good
}
Now I have done the exact same steps for a PointXYZRGB class which inherits from PointXYZ and when I try to test that it throws java.lang.UnsatisfiedLinkError. Here is the class:
package pcl;
public class PointXYZRGB extends PointXYZ {
public PointXYZRGB() { }
#Override
public native void alloc();
#Override
public native void dispose();
public native short getR();
// ...
}
I have checked the generated .dll using Dependency Walker and the PointXYZRGB methods are all present. Anyone knows what the problem could be?
UPDATE: Here are the .dll functions as requested in the comment:
The problem was that System.setProperty("java.library.path", System.getProperty("user.dir") + "/lib"); does not actually make Java look for .dll files in the given path. It essentially does nothing. Then why do the tests work for PointXYZ? This is was my mistake of having put an older .dll into the project root folder, so it was essentially looking for methods in that.
SQLUtils.java:
import org.openide.util.Lookup;
import java.util.ServiceLoader; // This doesn't work either
public class SQLUtils {
public static DBDriver getDriver(String prefix) {
for(DBDriver e : Lookup.getDefault().lookupAll(DBDriver.class)) {
System.out.println(e.getPrefix());
if(e.getPrefix().equalsIgnoreCase(prefix)) {
return e;
}
}
return null;
}
}
MySQLDriver.java:
public class MySQLDriver implements DBDriver {
#Override
public String getPrefix() {
return "mysql";
}
}
DBDriver.java:
import java.io.Serializable;
public interface DBDriver extends Serializable {
public String getPrefix();
}
Main.java:
public class Main {
public static void main(String[] args) {
DBDriver d = SQLUtils.getDriver("mysql");
}
}
This does nothing when running it, it cannot find any classes implementing.
What the program is trying to do is get the driver that is entered as a parameter for SQLUtils.getDriver(String prefix) (in Main.java).
For some reason I cannot get this to work.
I'm not familiar with OpenIDE Lookup mechanism, but I am familiar with the Java ServiceLoader mechanism.
You need to provide a file in the META-INF/services/ folder describing what classes implement specific interfaces. From the Java Docs describing the ServiceLoader class is this example:
If com.example.impl.StandardCodecs is an implementation of the
com.example.CodecSet service then its jar file also contains a file
named
META-INF/services/com.example.CodecSet
This file contains the single line:
com.example.impl.StandardCodecs # Standard codecs implementing com.example.CodecSet
What you are missing is a similar file that needs to be included on your classpath or within your JAR file.
You don't include you package names so I cannot provide a more direct example to help solve your problem.
I dropped the NetBeans API and switched to Reflections. I implemented Maven and ran it with IntelliJ. Works well for me.
I need to call Windows Color System functions from Java. Following this tutorial i tried to call DLL function using Java Native Access. All examples from this tutorial works fine. When i try to load and use Mscms.dll (one of the WCS libraries) that DLL seems to be loaded successfully, but i can not call any functions. List of functions is here.
I got a message:
Exception in thread "main" java.lang.UnsatisfiedLinkError: Error looking up function 'GetColorDirectory'
What's wrong with my code? Could you help me please?
import com.sun.jna.Library;
import com.sun.jna.Native;
public class WCS_test {
public interface Mscms extends Library {
// http://msdn.microsoft.com/en-us/library/dd316928%28v=vs.85%29.aspx
boolean GetColorDirectory(String pMachineName, String[] pBuffer, int pdwSize);
}
private static Mscms mscms = (Mscms) Native.loadLibrary("C:/Windows/system32/Mscms.dll", Mscms.class);
public static void main(String[] args) {
if (mscms != null)
System.out.println("Library loaded\n");
else
System.err.println("Library loading error\n");
String[] pBuffer = new String[1024];
mscms.GetColorDirectory(null, pBuffer, pBuffer.length);
}
}
When you get a java.lang.UnsatisfiedLinkError that means that it could not find the function 'GetColorDirectory' inside of the Mscms.dll. Looking at the link from your source code http://msdn.microsoft.com/en-us/library/dd316928%28v=vs.85%29.aspx you should try the Unicode name GetColorDirectoryW.
I have created a Mac Java Swing application, and i have set a file extension(*.pkkt) for it in the "Info.plist" file, so when double clicking that file it opens my application.
When i do that the program runs fine. Now i need to load the (*.pkkt) project in the program, but the file path is not passed as an argument to the main(...) method in Mac as happens in Windows Operating System.
After some search i found an Apple handling jar "MRJToolkitStubs" that has the MRJOpenDocumentHandler interface to handle such clicked files. I have tried using it to load that file by implementing that Interface in the main program class, but it is not working. The implemented method is never called at the program start-up.
How does this Interface run ?
------------------------------------------------- Edit: Add a Code Sample
Here is the code i am using :
public static void main( final String[] args ) {
.
.
.
MacOpenHandler macOpenHandler = new MacOpenHandler();
String projectFilePath = macOpenHandler.getProjectFilePath(); // Always Empty !!
}
class MacOpenHandler implements MRJOpenDocumentHandler {
private String projectFilePath = "";
public MacOpenHandler () {
com.apple.mrj.MRJApplicationUtils.registerOpenDocumentHandler(this) ;
}
#Override
public void handleOpenFile( File projectFile ) {
try {
if( projectFile != null ) {
projectFilePath = projectFile.getCanonicalPath();
System.out.println( projectFilePath ); // Prints the path fine.
}
} catch (IOException e) {}
}
public String getProjectFilePath() {
return projectFilePath;
}
}
As mentioned in the comment above "getProjectFilePath()" is always Empty !
On Java 9, use Desktop.setOpenFileHandler()
The proprietary com.apple.eawt packages have been removed from recent versions of Java and has been incorporated into various methods in the Desktop class. For your specific example:
import java.awt.desktop.OpenFilesHandler;
import java.awt.desktop.OpenFilesEvent;
import java.io.File;
import java.util.List;
public class MyOpenFileHandler implements OpenFilesHandler {
#Override
public void openFiles​(OpenFilesEvent e) {
for (File file: e.getFiles​()) {
// Do whatever
}
}
}
Then elsewhere, add this:
Desktop.getDesktop().setOpenFileHandler(new MyOpenFileHandler());
The OpenFilesEvent class also has a getSearchTerm() method. Say that a person used Spotlight on macOS to search for the word "StackOverflow", then decided to open up a document. With this method, can you determine that "StackOverflow" was the word they searched for, and choose to do something with that (perhaps highlight the first occurrence of the word).
You're going to want to use the Apple Java Extensions.
They should be included in any JDK that runs on Mac OS X, but the documentation is kind of hard to get. See this answer for more details.
Specifically, you'll want to make an OpenFilesHandeler.
This code snippet should work:
import com.apple.eawt.event.OpenFilesHandeler;
import com.apple.eawt.event.AppEvent;
import java.io.File;
import java.util.List;
class MacOpenHandler implements OpenFilesHandeler {
#Override
public void openFiles(AppEvent.OpenFilesEvent e) {
List<File> files = e.getFiles();
// do something
}
}
And somewhere:
import com.apple.eawt.Application;
...
MacOpenHandeler myOpenHandeler = new MacOpenHandeler();
Application.getApplication().setOpenFileHandler(myOpenHandeler);