import j ava.io.*;
import j ava.net.*;
import java.util.*;
class Webserver {
   public static void main(String argv[]) throws Exception
   {
      String requestMessageLine;
      String fileName;
      ServerSocket listenSocket = new ServerSocket(6789);
      Socket connectionSocket = listenSocket.accept();
      BufferedReader inFromClient =
         new BufferedReader(new InputStreamReader(
                connectionSocket.get!nputStream()));
      DataOutputStream outToClient =
         new DataOutputStream(
                connectionSocket.getOutputStream());
   requestMessageLine = inFromClient.readLine();
 
   StringTokenizer tokenizedLine = 
       new StringTokenizer(requestMessageLine);   if (tokenizedLine.nextToken().equals("GET")){       fileName = tokenizedLine.nextToken();       if (fileName.startsWith("/") == true )
               fileName = fileName.substring(1);
  File file = new File(fileName);     int numOfBytes = (int) file.length();     FileInputStream inFile = new FileInputStream (fileName);     byte[] fileInBytes = new byte[numOfBytes];     inFile.read(fileInBytes);
 outToClient.writeBytes(
                 "HTTP/I.0 200 Document Follows\r\n");
     if (fileName.endsWith(".jpg"))
         outToClient.writeBytes("Content-Type:image/jpeg\r\n");
     if (fileName.endsWith(".gif"))
        outToClient.writeBytes("Content-Type:image/gif\r\n");
     outToClient.writeBytes("Content-Length: " + 
               numOfBytes + "\r\n");
     outToClient.writeBytes("\r\n") ;
     outToClient.write(fileInBytes, 0, numOfBytes);
     connectionSocket.close();
     }
  else System.out.println("Bad Request Message");
  }
}即把这个改成多线程的,请问怎么改啊??