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org.postgres.Driver Class Exception - Beginner

thanks for any help, I am a complete noob here but trying to learn.
the below code is simply trying to create a connection to a database. I am getting this error back:
java.lang.ClassNotFoundException: org.postgres.Driver
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at CreateDB.main(CreateDB.java:11)
java.lang.ClassNotFoundException: org.postgres.Driver
having researched online the solution i come across is to check the library is added to to build path. i can confirm that i have (I think). to do this i right clicked the prject -> Properties -> Java Build Path -> external JARS and navigated to the postgresql - 42.41.4..jar which is located in "...\eclipse-workspace\libraries\"
I can see that the library is added under referenced libraries within the project.
not a clue now im stuck. any help is genuinely appreciated.
I am learning from here https://www.tutorialspoint.com/postgresql/postgresql_java.htm
import java.sql.Connection;
import java.sql.DriverManager;
public class CreateDB {
public static void main(String Args[]) {
Connection c = null;
try {
Class.forName("org.postgres.Driver");
c = DriverManager.getConnection("jdbc.postgresql://localhost:1080/VEM", "postgres", "Diablo12" ); //creates connection with U&P
} catch (Exception e) {
e.printStackTrace();
System.err.println(e.getClass().getName() +": " + e.getMessage());
System.exit(0);
}
System.out.println("Database opened successfully");
}
}

The correct driver name is: org.postgresql.Driver. So your code should look like this:
import java.sql.Connection;
import java.sql.DriverManager;
public class CreateDB {
public static void main(String args[]) {
Connection c = null;
try {
Class.forName("org.postgresql.Driver");
c = DriverManager.getConnection("jdbc.postgresql://localhost:1080/VEM", "postgres", "Diablo12" ); //creates connection with U&P
} catch (Exception e) {
e.printStackTrace();
System.err.println(e.getClass().getName() +": " + e.getMessage());
System.exit(0);
}
System.out.println("Database opened successfully");
}
}
The false driver name causes java to throw the ClassNotFoundException because the class with the passed name could not be found in the classpath.
Since Java 6 the loading of the driver via Class.forName() is not needed any more, like a_horse_with_no_name pointed out in his comment.

ClassNotFoundException with RMI

i wrote a program in netbeans with RMI that client has error
error :
java.rmi.UnmarshalException: error unmarshalling return; nested
exception is: java.lang.ClassNotFoundException: rmiserver.Message
(no security manager: RMI class loader disabled) at
sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
but sever does not any error!
interfaace code:
package rmiclient;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface Message extends Remote {
void sayHello(String name) throws RemoteException;
}
interface implementation is:
package rmiserver;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class MessageImpl extends UnicastRemoteObject implements Message {
public MessageImpl() throws RemoteException {
}
#Override
public void sayHello(String name) throws RemoteException {
System.out.println("hello "+name);
}
}
server code is:
package rmiserver;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class Main {
private void startServer(){
try {
// create on port 1099
Registry registry = LocateRegistry.createRegistry(1099);
// create a new service named myMessage
registry.rebind("myMessage", new MessageImpl());
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("system is ready");
}
public static void main(String[] args) {
Main main = new Main();
main.startServer();
}
}
client code is:
package rmiclient;
import java.rmi.RMISecurityManager;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class Main {
private void doTest(){
try {
// fire to localhost port 1099
Registry myRegistry = LocateRegistry.getRegistry("127.0.0.1", 1099);
// search for myMessage service
Message impl = (Message) myRegistry.lookup("myMessage");
// call server's method
impl.sayHello("edwin");
System.out.println("Message Sent");
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Main main = new Main();
main.doTest();
}
}
thanks :).

In your stacktrace:
java.lang.ClassNotFoundException: rmiserver.Message
but as per data you have provided, your Message interface is declated with package package rmiclient; and You haven't created any rmiserver.Message class.
Correct the package name.

I have two package. rmiclient and rmiserver. that in rmiclient are "message" and "main" . in rmiserver are "message" and "main" and "messageimpl"
That's your problem. This doesn't satisfy the contract. You can't just copy Message to another package and expect to have it be treated the same as the original. The remote stub implements the same remote interfaces that the remote object does. Not another interface with the same name in another package.
You have to deploy rmiserver.Message to the client. Just like the error message says, really.

RMI client cannot lookup server - java.rmi.UnmarshalException

I have a java rmi server and a java rmi client in two separate and different machines.
The server is basically a fibonacy calculator. It receives a bunch of numbers and calculates a Fibonacci sequence based on them.
The client simply sends a bunch of numbers for the server to calculate.
The FiboServer project consists of three classes:
IFibonacci.java: an interface
Fibonacci.java: implements the previously defined interface
FibonacciServer.java: Has the main, and runs the server
FibonacciServer.java:
package fiboserver;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class FibonacciServer {
public static void main(String args[]){
if (System.getSecurityManager() == null) {
System.setProperty("java.security.policy", "server.policy");
System.setSecurityManager(new SecurityManager());
}
try{
IFibonacci fib = new Fibonacci();
// Bind the remote object's stub in the registry
Registry registry = LocateRegistry.createRegistry(1099);
registry.rebind("fibonacci", fib);
System.out.println("Fibonacci Server ready.");
}catch(RemoteException rex){
System.err.println("Exception in Fibonacci.main " + rex);
}
}
}
The client project merely has one class: FibonacciClient.java.
FibonacciClient.java:
package fiboclient;
import fiboserver.IFibonacci;
import java.math.BigInteger;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class FibonacciClient {
public static void main(String[] args) {
if (System.getSecurityManager() == null) {
System.setProperty("java.security.policy", "client.policy");
System.setSecurityManager(new SecurityManager());
}
try{
//args[0] = server Public IP
Registry registry = LocateRegistry.getRegistry(args[0]);
IFibonacci calculator = (IFibonacci) registry.lookup("fibonacci");
//the rest of the args are just numbers to calculate
for(int i = 1; i < args.length; i++){
try{
BigInteger index = new BigInteger(args[i]);
BigInteger f = calculator.getFibonacci(index);
System.out.println("The " + args[i] + "th Fibonacci number "
+ "is " + f);
}catch(NumberFormatException e){
System.err.println(args[i] + " is not an integer.");
}
}
}catch(RemoteException e){
System.err.println("Remote object threw exception " + e);
} catch (NotBoundException e) {
System.err.println("Could not find the requested remote object on "
+ "the server: " + e);
}
}
}
Both projects have a policy file, the server has a server.policy and the client has a client.policy file. Both files have the same content:
grant{
permission java.security.AllPermission;
};
I am launching the FiboServer in the server machine using java -jar FiboServer.jar -Djava.net.preferIPv4Stack=true -Djava.rmi.server.hostname=12.34.56.789
I am launching the client by using java -jar FiboClient.jar 12.34.56.789 1 2 3 4 5.
The server launches without a problem. But when I launch the client I get the error:
Remote object threw exception java.rmi.UnmarshalException: error unmarshalling return; nested exception is:
java.lang.ClassNotFoundException: fiboserver.IFibonacci
Searches on StackOverflow convinced me that this has to do with RMI registry errors or policy file errors. However I know the the policy files are being read correctly and I do not think they have any errors.
What am I doing wrong? Why is this not working?
EDIT:
IFibonacci.java:
package fiboserver;
import java.math.BigInteger;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface IFibonacci extends Remote{
public BigInteger getFibonacci(int n) throws RemoteException;
public BigInteger getFibonacci(BigInteger n) throws RemoteException;
}
JAR Files:
Contents of FibonacciClient.jar:
|META-INF
|----Manifest.mf
|fiboclient
|----FibonacciClient.class
Contents of FibonacciServer.jar:
|META-INF
|----manifest.mf
|fiboserver
|----IFibonacci.class
|----FibonacciServer.class
|----Fibonacci.class

The client doesn't have the class named in the exception available on its classpath. You need to deploy it, and any class it depends in, and so on recursively until closure.
Possibly you've renamed/copied the remote interface into another package for the client. You can't do that. It has to be the same at server and client. Same name, same methods, same package.
NB The message in your client 'remote object threw exception' isn't correct. It could be the lookup() throwing the exception. Don't confuse yourself by assuming things that may not be so. Just print the actual error message, exception, and stack trace.

Asterisk-java for AMI not working correctly

I am an absolute newbee in asterisk. I am trying to use asterisk-java for event listening through AMI. I am currently using the version 11.2.1 asterisk. When I tries to compiles the code as
javac -cp asterisk-java-0.3.jar HelloEvents.java
it complets successfully. But when I try to execute the file, I give the following error.
Exception in thread "main" java.lang.NoClassDefFoundError: HelloEvents
Caused by: java.lang.ClassNotFoundException: HelloEvents
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: HelloEvents. Program will exit.
the code is
import java.io.IOException;
import org.asteriskjava.manager.AuthenticationFailedException;
import org.asteriskjava.manager.ManagerConnection;
import org.asteriskjava.manager.ManagerConnectionFactory;
import org.asteriskjava.manager.ManagerEventListener;
import org.asteriskjava.manager.TimeoutException;
import org.asteriskjava.manager.action.StatusAction;
import org.asteriskjava.manager.event.ManagerEvent;
public class HelloEvents implements ManagerEventListener
{
private ManagerConnection managerConnection;
public HelloEvents() throws IOException
{
ManagerConnectionFactory factory = new ManagerConnectionFactory(
"localhost", "manager", "password");
this.managerConnection = factory.createManagerConnection();
}
public void run() throws IOException, AuthenticationFailedException,
TimeoutException, InterruptedException
{
// register for events
managerConnection.addEventListener(this);
// connect to Asterisk and log in
managerConnection.login();
// request channel state
managerConnection.sendAction(new StatusAction());
// wait 10 seconds for events to come in
Thread.sleep(10000);
// and finally log off and disconnectaaaa
managerConnection.logoff();
}
public void onManagerEvent(ManagerEvent event)
{
// just print received events
System.out.println(event);
}
public static void main(String[] args) throws Exception
{
HelloEvents helloEvents;
helloEvents = new HelloEvents();
helloEvents.run();
}
}

java -cp ".;asterisk-java.jar" HelloEvents
works fine.
And the class path separator is OS dependent. If you are using linux / mac, use : (colon) instead of ; (semicolon)

We can avoid adding class path every time while compiling or executing code. Now go to the location where jar file is located. Then run,
For linux :- export CLASSPATH=$CLASSPATH:asterisk-java-2.0.3.jar:.
For windows:- set CLASSPATH=$CLASSPATH:asterisk-java-2.0.3.jar:.
Now compile code by
javac HelloEvents.java
Execute it by java HelloEvents

Java RMI application failed to run

I created a simple Java RMI application in netbeans 7.0.1 ( win 7 + jdk 7u1). I have two separate projects:
RMI_Client contains:
MyClient class:
package rmi_client;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class MyClient
{
public static void main(String[] args)
{
String msg = "Hello RMI";
rmiInterface stub;
Registry reg;
try
{
reg = LocateRegistry.getRegistry("localhost");
stub = (rmiInterface) reg.lookup("Hello");
try
{
stub.hello(msg);
}
catch(Exception e)
{
System.out.println("Remote method exception thrown: " +e.getMessage());
}
}
catch(Exception e)
{
System.err.println("Client exception thrown: " + e.toString());
e.printStackTrace();
}
}
}
rmiInterface interface:
package rmi_client;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface rmiInterface extends Remote
{
void hello(String message) throws RemoteException;
}
RMI_Server contains:
rmiInterface interface - exactly the same as above
rmiImpl class:
package rmi_server;
import java.rmi.RemoteException;
public class rmiImpl implements rmiInterface
{
#Override
public void hello(String message) throws RemoteException
{
System.out.println("Server:" + message);
}
}
MyServer class:
package rmi_server;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;
public class MyServer
{
public static void main(String[] args)
{
try
{
rmiImpl robj = new rmiImpl();
rmiInterface stub = (rmiInterface) UnicastRemoteObject.exportObject(robj, 0);
Registry reg = LocateRegistry.createRegistry(1099);
reg.rebind("Hello", stub);
System.out.println("Server is ready to listen: ");
}
catch (Exception e)
{
System.err.println("Server exception thrown: " + e.toString());
}
}
}
If I'm doing something wrong above please let me know. First I start RMI_Server application, then when I run RMI_Client I get errors:
Client exception thrown: java.rmi.UnmarshalException: error unmarshalling return; nested exception is:
java.lang.ClassNotFoundException: rmi_server.rmiInterface (no security manager: RMI class loader disabled)
java.rmi.UnmarshalException: error unmarshalling return; nested exception is:
java.lang.ClassNotFoundException: rmi_server.rmiInterface (no security manager: RMI class loader disabled)
at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
at rmi_client.MyClient.main(MyClient.java:28)
Caused by: java.lang.ClassNotFoundException: rmi_server.rmiInterface (no security manager: RMI class loader disabled)
at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:554)
at java.rmi.server.RMIClassLoader$2.loadProxyClass(RMIClassLoader.java:646)
at java.rmi.server.RMIClassLoader.loadProxyClass(RMIClassLoader.java:311)
at sun.rmi.server.MarshalInputStream.resolveProxyClass(MarshalInputStream.java:257)
at java.io.ObjectInputStream.readProxyDesc(ObjectInputStream.java:1549)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1511)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1750)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
... 2 more
Where is the problem ?

RMI_Server contains:
rmiInterface interface - exactly the same as above
No it isn't. This message:
java.lang.ClassNotFoundException: rmi_server.rmiInterface
says that rmiinterface is in the rmi_server package, which isn't 'the same as above'.
It has to be exactly the same class. Not a similar class in a different package.
So what you need is three packages: server, client, and shared. The shared package needs to contain the remote interface and any application classes it relies on.