أحاول حل سؤال عن ال Multithreading بين client و server، المفترض أن ال client يستيطع إرسال أربع أوامر فقط ويتعامل مع كل منها ال server بالشكل التالي:
1-إن أرسل ال client الأمر ADD filename فإن ال server سيضيف إسم الملف إلى ال data structure التي ستخزن أسماء الملفات في ال server.
2-إن أرسل ال client الأمر LSF فإن السيرفر سيقوم بعرض قائمة بأسماء الملفات التي يحويها.
3-إن أرسل ال client الأمر SRC فإن السيرفر سيقوم بعرض رقم ال ID لل file's owner.
4- إن أرسل ال client الأمر QUIT فسيخرج.
الحاصل أني أواجه مشكلة NullPointerException ، أظن أنها مع variable إسمه clientCommand لكن بحسب علمي أني قد أعلنت له object مسبقاً فهو يستطيع وعملت له initialization فلا أعلم مشكلة فيه!.
هل أحد من الأخوة يستطيع مساعدتي في الأمر...
الكودين كالتالي:
Server code:
//kazaaServer.java : The Server application
import java.net.*;
import java.io.*;
import java.util.*; // for Tokenizer
public class KazaaServer
{
ServerSocket m_ServerSocket;
String[] files = new String[100];
public KazaaServer()
{
try
{
// Create the server socket.
m_ServerSocket = new ServerSocket(12111);
}
catch(IOException ioe)
{
System.out.println("Could not create server socket at 12111. Quitting.");
System.exit(-1);
}
System.out.println("Listening for clients on 12111...");
// Successfully created Server Socket. Now wait for connections.
int id = 0;
while(true)
{
try
{
// Accept incoming connections.
Socket clientSocket = m_ServerSocket.accept();
// accept() will block until a client connects to the server.
// If execution reaches this point, then it means that a client
// socket has been accepted.
// For each client, we will start a service thread to
// service the client requests. This is to demonstrate a
// multithreaded server, although not required for such a
// trivial application. Starting a thread also lets our
// EchoServer accept multiple connections simultaneously.
// Start a service thread
ClientServiceThread cliThread = new ClientServiceThread(clientSocket, id++);
cliThread.start();
}
catch(IOException ioe)
{
System.out.println("Exception encountered on accept. Ignoring. Stack Trace :");
ioe.printStackTrace();
}
}
} // public KazaaServer
public static void main (String[] args)
{
new KazaaServer();
}
class ClientServiceThread extends Thread
{
Socket m_clientSocket;
int m_clientID = -1;
boolean m_bRunThread = true;
ClientServiceThread(Socket s, int clientID)
{
m_clientSocket = s;
m_clientID = clientID;
}
public void run()
{
// Obtain the input stream and the output stream for the socket
// A good practice is to encapsulate them with a BufferedReader
// and a PrintWriter as shown below.
String clientCommand = new String();
clientCommand=" ";
BufferedReader in = null;
PrintWriter out = null;
int ID=0;
// Print out details of this connection
System.out.println("Accepted Client : ID - " + m_clientID + " : Address - " +
m_clientSocket.getInetAddress().getHostName());
try
{
in = new BufferedReader(new InputStreamReader(m_clientSocket.getInputStream()));
out = new PrintWriter(new OutputStreamWriter(m_clientSocket.getOutputStream()));
// At this point, we can read for input and reply with appropriate output.
// Run in a loop until m_bRunThread is set to false
while(m_bRunThread)
{
//String clientCommand = new String();
//clientCommand= " ";
// read incoming stream
// BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
//String clientCommand = "";
clientCommand = in.readLine();
String[] tokens = new String[2];
StringTokenizer st = new StringTokenizer(clientCommand," ");
int i=0;
while (st.hasMoreTokens() ) {
tokens[i++] = st.nextToken();
}
if(tokens[0]=="ADD"){
files[ID++]=tokens[1];
}
if(tokens[0]=="SRC"){
for(i=0;i<ID;i++){
if(tokens[1]==files){
out.print("the owner is :");
out.println(i);
}
}
}
if(clientCommand.equalsIgnoreCase("LSF"))
{
for(i=0;i<ID;i++){
out.println(files);
}
}
if(clientCommand.equalsIgnoreCase("quit"))
{
// Special command. Quit this thread
m_bRunThread = false;
System.out.print("Stopping client thread for client : " + m_clientID);
}
else
{
// Echo it back to the client.
out.println(clientCommand);
out.flush();
}
} //while
} //try
catch(Exception e)
{
e.printStackTrace();
}
finally
{
// Clean up
try
{
in.close();
out.close();
m_clientSocket.close();
System.out.println("...Stopped");
}
catch(IOException ioe)
{
ioe.printStackTrace();
}
}//finally
} //run
} //ClientServiceThread
} // kazaaserverClient code:
//KazaaClient.java : The client application
import java.net.*;
import java.io.*;
import java.util.*;
// A client for our multithreaded EchoServer.
public class KazaaClient
{
public static String[] args= new String[1];//{PC148716230145};
public static void main(String[] args)
{
// First parameter has to be machine name
args[0]="127.0.0.1";//if it doesn't work within your JDT,you compile the .java file then take the .class file copy it in \bin directory in j2sd directory then run it from DOS prompt
if(args.length == 0)
{
System.out.println("Usage : EchoClient <serverName>");
return;
}
Socket s = null;
// Create the socket connection to the EchoServer.
try
{
s = new Socket(args[0], 12111);
}
catch(UnknownHostException uhe)
{
// Host unreachable
System.out.println("Unknown Host :" + args[0]);
s = null;
}
catch(IOException ioe)
{
// Cannot connect to port on given host
System.out.println("Cant connect to server at 12111. Make sure it is running.");
s = null;
}
if(s == null)
System.exit(-1);
BufferedReader inCommand = null;
PrintWriter out = null;
String line;
try
{
// Create the streams to send and receive information
inCommand = new BufferedReader(new InputStreamReader(s.getInputStream()));
out = new PrintWriter(new OutputStreamWriter(s.getOutputStream()));
System.out.print("Enter your command: ");
// read the command from the command-line; need to use try/catch with the
// readLine() method
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String cmd = null;
try {
cmd = br.readLine();
} catch (IOException ioe) {
System.out.println("IO error trying to read your command!");
System.exit(1);
}
out.print(cmd);
// open up standard input
//BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
/*String cmd = null;
String[] tokens = new String[2];
// read the command from the command-line; need to use try/catch with the
// readLine() method
try {
cmd = br.readLine();
} catch (IOException ioe) {
System.out.println("IO error trying to read your command!");
System.exit(1);
}
StringTokenizer st = new StringTokenizer(cmd, " ,\t");
int i=0;
while (st.hasMoreTokens()) {
tokens[i++] = st.nextToken();
}
System.out.println(tokens[0]);*/
}
catch(IOException ioe)
{
System.out.println("Exception during communication. Server probably closed connection.");
}
finally
{
try
{
// Close the streams
out.close();
inCommand.close();
// Close the socket before quitting
s.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
}