Develop Reference

JavaFX app overwriting files while being open causes exception

I have a runnable jar file (with a lib folder housing all the dependency jars). This is located on a network share which anyone that has access can run from. This works great except one huge caveat. If I want to deploy a new version of the software, I have to ask everyone to exit the application first. This is because if I overwrite the jars with new versions (or if there is a network blip), the running program stays open but as soon as they do an action that requires code in of the dependencies (jar file in lib folder), it will cause an exception:
Exception in thread "JavaFX Application Thread" java.lang.NoClassDefFoundError
The program will not produce an error, but certain actions will break, like communicating with an API etc.
Is there a way that I can resolve this so that I can publish updates while the user's are working or at least produce a prompt that will force them to close/and reopen the app etc.

One approach:
Provide a script which launches the application from a local copy of the remote code.
Store a version number with your app.
The script checks if there is a local copy of the app on the machine.
If no local version exists, the script copies the jars from your network share to a local copy.
If there is already a local copy, it checks the version against the network version.
If the network version is updated, it overwrites the local copy with the new remote version before launching the app,
otherwise it just launches the local copy.
If you want the users to be alerted that they are currently running an outdated copy, you could create a JavaFX task which polls the remote version number and checks it against the currently running version number. If they differ, you can alert and (if you wish) shutdown the app and re-trigger the launcher script.

I was able to create a scheme in which I have multiple server folder locations that house the jar distributable. And this jar basically checks these locations for the latest copy of the application and runs that latest copy. I was able to get it working for both Mac and Windows (didn't test Linux) by detecting the OS.
So now, I can publish an update over the oldest app, and the next time the user opens the app, it will be the latest copy.
process.properties
location.a=Application/A
location.b=Application/B
app=app.jar
You can add folders A-Z but just add them into the properties.
Main.java
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.TreeMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.apache.commons.io.FileUtils;
import org.apache.commons.lang3.StringUtils;
public class Main
{
public static Properties properties;
private static final String DEFAULT_PROPERTY_FILE_LOCATION = Paths.get("").toAbsolutePath().toString() + File.separator + "process.properties";
private static final String JAVE_EXEC;
static
{
String os = System.getProperty("os.name");
if (StringUtils.containsIgnoreCase(os, "win"))
{
JAVA_EXEC = "java";
} else if (StringUtils.containsIgnoreCase(os, "mac"))
{
JAVA_EXEC = "/usr/bin/java";
} else if (StringUtils.containsIgnoreCase(os, "nux") || StringUtils.containsIgnoreCase(os, "nix"))
{
JAVA_EXEC = "/usr/bin/java";
} else
{
JAVA_EXEC = "java";
}
}
/**
* #param args the command line arguments
*/
public static void main(String[] args)
{
Main.properties = new Properties();
try
{
InputStream in = new FileInputStream(DEFAULT_PROPERTY_FILE_LOCATION);
Main.properties.load(in);
System.out.println("Loaded property file: " + DEFAULT_PROPERTY_FILE_LOCATION);
TreeMap<Long, String> locations = new TreeMap<>();
String appName = Main.properties.getProperty("app");
if (validateProperties(properties))
{
for (int letter = 'a'; letter <= 'z'; ++letter)
{
String location = "location." + (char) letter;
if (Main.properties.getProperty(location) != null)
{
String networkLocation = Paths.get("").toAbsolutePath() + File.separator + Main.properties.getProperty(location);
File file = new File(networkLocation + File.separator + appName);
if (file.exists())
{
locations.put(FileUtils.lastModified(file), networkLocation);
}
}
}
if (!locations.isEmpty())
{
Runtime.getRuntime().exec(new String[]
{
JAVA_EXEC, "-jar", locations.lastEntry().getValue() + File.separator + appName
}, null, new File(locations.lastEntry().getValue()));
}
}
} catch (IOException ex)
{
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
}
}
private static boolean validateProperties(Properties properties)
{
List<String> mandatoryProperties = new ArrayList<>();
mandatoryProperties.add("app");
for (String mandatoryProperty : mandatoryProperties)
{
if (properties.get(mandatoryProperty) == null)
{
System.out.println("Failed - Property: " + mandatoryProperty + " doesn't exist.");
return false;
}
}
return true;
}
}

Spigot Minecraft plugin coding NoClassDefFound error mysql

When i start the server this error comes :
I am using IntelliJ Idea and MySQL jar is added to the src and in the project modules.
Error pastebin
Here is my code
package com.okaam.jaajhome;
import org.bukkit.plugin.java.JavaPlugin;
import pro.husk.mysql.MySQL;
import java.sql.Connection;
import java.sql.SQLException;
public class JaaJHome extends JavaPlugin {
static JaaJHome instance = null;
MySQL MySQL = new MySQL("address", "port", "schema", "user", "password", "");
static Connection c = null;
#Override
public void onEnable() {
System.out.println("Plugin JaaJHome active");
getCommand("sethome").setExecutor(new SetHomeExecutor());
getCommand("home").setExecutor(new HomeExecutor());
try {
c = MySQL.getConnection();
} catch (SQLException e) {
e.printStackTrace();
}
instance = this;
}
public static JaaJHome getInstance() {
return instance;
}
}

It seems like you're missing on some dependencies, make sure you have them either in the plugins folder as a non plugin or in the classpath to make sure they're loaded.

Java Current Directory Returns `null`

I'm trying to use the printWorkingDirectory() from Apache Commons FTP but it's only returning null. I can't navigate directories, list files, etc.
Log in pass all is success but how ever I try I can not change current directory.
I use this following code:
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
public class FTPDownloadFileDemo {
public static void main(String[] args) {
String server = "FTP server Address";
int port = portNo;
String user = "User Name";
String pass = "Pasword";
FTPClient ftpClient = new FTPClient();
String dir = "stocks/";
try {
ftpClient.connect(server, port);
ftpClient.login(user, pass);
System.out.println( ftpClient.printWorkingDirectory());//Always null
//change current directory
ftpClient.changeWorkingDirectory(dir);
boolean success = ftpClient.changeWorkingDirectory(dir);
// showServerReply(ftpClient);
if (success)// never success
System.out.println("Successfully changed working directory.");
System.out.println(ftpClient.printWorkingDirectory());// Always null
} catch (IOException ex) {
System.out.println("Error: " + ex.getMessage());
ex.printStackTrace();
} finally {
try {
if (ftpClient.isConnected()) {
ftpClient.logout();
ftpClient.disconnect();
}
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
}

This is rather old question that deserves an answer. This issue is likely a result of using FTPClient when secure connection is required. You may have to switch to FTPSClient if that is, indeed, the case. Further, output the response from the server with the following code snippet to troubleshoot the issue if secure client doesn't solve the it:
ftpClient.addProtocolCommandListener(
new PrintCommandListener(
new PrintWriter(new OutputStreamWriter(System.out, "UTF-8")), true));
Also, a server can reject your login attempt if your IP address is not white listed. So, being able to see the logs is imperative. The reason you see null when printing current working directory is because you are not logged in. Login method will not throw an exception but rather return a boolean value indicating if the operation succeeded. You are checking for success when changing a directory but not doing so when logging in.
boolean success = ftpClient.login(user, pass);

I faced the same, but I came across with a simple step.
Just added this.
boolean success = ftpClient.changeWorkingDirectory(dir);
ftpClient.printWorkingDirectory(); //add this line after changing the working directory
System.out.println(ftpClient.printWorkingDirectory()); //wont be getting null
Here I have the code and the console output
FTPClient.changeWorkingDirectory - Unknown parser type: "/Path" is current directory
I know I replied too soon ;-P, but I saw this post recently. Hope this helps to future searchers ;-)

java.lang.NoClassDefFoundError

I have no idea of why this is having a runtime error, I have googled the problem and it says that a class that was available during compile time is no longer available at run time.
This is the code:
package examples.RMIShape;
import java.rmi.*;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
//import java.rmi.server.UnicastRemoteObject;
public class ShapeListServer {
public static void main(String args[]){
// System.setSecurityManager(new RMISecurityManager());
System.out.println("Main OK");
try{
ShapeList aShapelist = new ShapeListServant();
System.out.println("After create");
String registryURL = "rmi://localhost:" + "/ShapeList";
startRegistry();
Naming.rebind(registryURL, aShapelist);
System.out.println("ShapeList server ready");
}catch(Exception e) {
System.out.println("ShapeList server main " + e.getMessage());
}
}
// This method starts a RMI registry on the local host, if it
// does not already exists at the specified port number.
private static void startRegistry()throws RemoteException{
Registry registry;
try {
registry = LocateRegistry.getRegistry();
registry.list( ); // This call will throw an exception
// if the registry does not already exist
}
catch (RemoteException e) {
// No valid registry at that port.
System.out.println ("RMI registry cannot be located at port " + Registry.REGISTRY_PORT );
registry = LocateRegistry.createRegistry(Registry.REGISTRY_PORT);
System.out.println("RMI registry created at port " + Registry.REGISTRY_PORT);
}
} // end startRegistry
}

I have googled the problem and it says that a class that was available during compile time is no longer available at run time.
That's not correct. That would cause ClassNotFoundException. This one has several causes, but the most common one is that the class in the file isn the class implied by the filename and directory hierarchy.

Basicall java.lang.NoClassDefFoundError thrown if the Java Virtual Machine or a ClassLoader instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found.
following links will be helpful. This links will guide you slove issue.
http://javarevisited.blogspot.in/2011/06/noclassdeffounderror-exception-in.html
http://javaeesupportpatterns.blogspot.in/2012/06/javalangnoclassdeffounderror-how-to.html
Hope this will be helpful

Using reflections with onejar plugin

I am using reflections with onejar maven plugin, and I have a problem when running the resulting jar:
20204 [main] ERROR org.reflections.Reflections - given scan urls are
empty. set urls in the configuration
It seems to me that reflections doesn't support the class loader that onejar is using. I've been using the following configuration of Reflections in my code:
Reflections reflections = new Reflections("path.to.my.package");
Any ideas? Thanks.

Yep a known issue. There is a work around...
Use Custom UrlType and custom Vfs.Dir; Uses OneJarURLConnection to correctly read content from embedded JARs; uses 'standard' Vfs.File.
Issue and solution discussed here : http://code.google.com/p/reflections/issues/detail?id=128
Source if you need it:
OneJarDir
package com.sdl.ws.integration.profserv.shared.onejar;
import com.simontuffs.onejar.OneJarURLConnection;
import org.reflections.vfs.Vfs;
import org.reflections.vfs.ZipDir;
import org.reflections.vfs.ZipFile;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
public class OneJarDir implements Vfs.Dir {
private JarFile oneJarFile = null;
private List<Vfs.File> oneJarClassFiles = new ArrayList<Vfs.File>();
private OneJarURLConnection oneJarConnection;
public OneJarDir(OneJarURLConnection oneJarConnection) {
this.oneJarConnection = oneJarConnection;
try {
this.oneJarConnection.connect();
this.oneJarFile = this.oneJarConnection.getJarFile();
Enumeration<JarEntry> entries = oneJarFile.entries();
while (entries.hasMoreElements()) {
oneJarClassFiles.add(new ZipFile(new ZipDir(oneJarFile), entries.nextElement()));
}
} catch (IOException e) {
throw new RuntimeException("Can't create One-Jar VFS directory", e);
}
}
public String getPath() {
return oneJarConnection.getURL().getPath();
}
public Iterable<Vfs.File> getFiles() {
return oneJarClassFiles;
}
public void close() {
try {
if (oneJarConnection != null)
oneJarConnection.getInputStream().close();
} catch (IOException e) {
throw new RuntimeException("Can't close VFS JAR stream", e);
}
}
}
OneJarUrlType
package com.sdl.ws.integration.profserv.shared.onejar;
import com.simontuffs.onejar.OneJarURLConnection;
import org.reflections.vfs.Vfs;
import java.io.IOException;
import java.net.URL;
public class OneJarUrlType implements Vfs.UrlType {
private static final String _JAR_DIR = "jar!";
public boolean matches(URL url) {
// check if "double-jarred' by one-jar; this would appear to conflict with the standard JAR loader, so it either needs to be first (which it is)
// OR the standard needs to be removed. This match assumes a nested JAR, unlike the standard JAR type.
String externalForm = url.toExternalForm();
// ugly, but should be much faster than regex.
int idx1 = externalForm.indexOf(_JAR_DIR);
return (idx1 > 0 && externalForm.indexOf(_JAR_DIR, idx1 + _JAR_DIR.length()) > 0);
}
public Vfs.Dir createDir(URL url) {
try {
return new OneJarDir(new OneJarURLConnection(url));
} catch (IOException e) {
throw new RuntimeException("Can't open One-Jar embedded JAR", e);
}
}
}