PostgreSQL驱动程序ClassNotFoundException错误

Question

我已经看到很多不同的方法可以解决此问题，但是没有一个方法可以解决此问题。错误是这样的：

    java.lang.ClassNotFoundException: org.postgresql.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 questionarios.DBConn.connectDB(DBConn.java:35)
    at questionarios.questionariosImpl.addQuest3(questionariosImpl.java:144)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
    at sun.rmi.transport.Transport$1.run(Unknown Source)
    at sun.rmi.transport.Transport$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Unknown Source)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

我见过很多解决方案：环境变量，路径，类路径，库的jar，连接到数据库（我在NetBeans上尝试过，并且连接没有问题）。我还能做些什么？谢谢