Java Reflection API problem... Please HELP!

Question

Hi,
I'm writing a Client-Server program set where the Server class receives a Java file, along with some parameters, from the Client class/computer.
The Server class then invokes a certain method from the Java file it received (depending on the parameters received).
My Server program keeps giving me a ClassNotFoundException, and I'm going crazy.. I've been trying to fix it for a long time now... but with no avail.
Here's the Server program.. but I doubt you need to read it all. Please just scroll down to "// The line below is what give me problems:".
package remoterun;
import java.net.*;
import java.io.*;
import java.lang.reflect.*;
* <p>Copyright: Copyright ms2000 (c) 2005</p>
public class Server2 {
    public static void main(String args[]) throws Exception {
        int numParameters;
        int port = 6789;
        boolean isThere = false;
        String className, methodName;
        Object[] parameters;
        ServerSocket welcomeSocket = new ServerSocket(port);
        for (; ; ) {
             * Create a new socket, called connectionSocket, when some client knocks
             * on welcomeSocket. This socket has the same port number. TCP then
             * establishes a direct virtual pipe between the client socket and
             * connectionSocket at the server so the client and server can send bytes
             * to each other over it.
            Socket connectionSocket = welcomeSocket.accept();
            // Get number of parameters
            DataInputStream in = new DataInputStream(new BufferedInputStream(
                    connectionSocket.getInputStream()));
            numParameters = in.readInt();
// Get the parameters for the method to be invoked.
            parameters = new Object[numParameters];
            ObjectInputStream objStream = new ObjectInputStream(
                    connectionSocket.getInputStream());
            for (int i = 0; i < numParameters; i++) {
                parameters[i] = objStream.readObject();
            // read the class
            File program = (File) objStream.readObject();
            System.err.println(program); // It prints the program name correctly, e.g. Class2.java
// Receiving some String parameters...
                        BufferedReader inFromClient = new BufferedReader(new
                    InputStreamReader(connectionSocket.getInputStream()));
            className = inFromClient.readLine();
            methodName = inFromClient.readLine();
            // The line below is what give me problems:
            Class classDefinition = Class.forName("remoterun." + className + ".java");
            Object object = classDefinition.newInstance();
            Method[] theMethods = classDefinition.getMethods();
            for (int i = 0; (i < theMethods.length) && (!isThere); i++) {
                if (theMethods.getName().equals(methodName)) {
isThere = true;
theMethods[i].invoke(object, parameters);
The Client code just sends the stuff to the Server, and it works fine. The code is below if it may help:
package remoterun;
import java.net.*;
import java.io.*;
public class Client2 {
    public static void main(String[] args) throws Exception {
        int result;
        int port = 6789;
        int num1 = 5;
        int num2 = 6;
        int numParameters = 3;
        String hostIP = "127.0.0.1";
        String className = "Class2";
        String methodName = "add";
        Object[] parameters;
        Socket clientSocket = new Socket(InetAddress.getByName(hostIP),
                                         port);
        // Send numParameters, className, methodName
        DataOutputStream out = new DataOutputStream(new BufferedOutputStream(
                clientSocket.getOutputStream()));
        out.writeInt(numParameters);
        out.flush();
        Integer num3 = new Integer(num1);
        Integer num4 = new Integer(num2);
        parameters = new Object[] {num3, num4, InetAddress.getLocalHost()};
        File program = new File((className + ".java"));
        ObjectOutputStream output = new ObjectOutputStream(clientSocket.
                getOutputStream());
        for (int i = 0; i < numParameters; i++) {
            output.writeObject(parameters);
output.writeObject(program);
output.flush();
DataOutputStream outToServer = new DataOutputStream(clientSocket.
getOutputStream());
outToServer.writeBytes(className + '\n');
outToServer.writeBytes(methodName + '\n');
outToServer.flush();
clientSocket.close();
The error I get from the Server class is:
java.lang.ClassNotFoundException: remoterun.Class2.java
at java.net.URLClassLoader$1.run(URLClassLoader.java:199)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:141)
at remoterun.Server2.main(Server2.java:94)
Exception in thread "main"
(I also get a dialog box saying sthg like, "A fatal exception occured.. will exit now".)
It's really odd, becuase there were rare times when it works although I don't change the program...
I tried changing the problem line to stuff like:
            Class classDefinition = Class.forName(className + ".java");or
   Class classDefinition = Class.forName(className);but with no use. Same error. Can someone please pinpoint the problem?
I'm sure the program does get to the Server, because it can print out the file name.
PS: Sometimes it works when I use the same PC as the client/server, sometimes it doesn't.... Help :-(
I'd appreciate some assistance in this.
Thank you.

Answer 1

What's this dot-java stuff? Are you sending a source file? If so, that isn't going to work. You need to compile the file and send the dot-class file.
I'll try that. However, can I make the Client program complie the .java file? For example. something like Class2.compile()? Is this feature available, or do I have to open Class2.java and compile it from there?
And in the server you need to either store that somewhere in the server's classpath....
Isn't it automatically stored there? If not, how do I make it stored in the same file as the Server source file (I assume that's what you mean by classpath)?
Thanks for your help... !!!