java-serverside for（;;）循環在readline（）爲null時停止

Question

我有幾個關於我的服務器端代碼的問題。由於我不知道如何調試服務器端代碼，我在這裏問它可能是什麼原因。在我的for(;;)循環，如果信息來了nullfor循環休息之前來到我的if(msg==null)聲明，所以我不能播出它可能是什麼問題？由於

public class ChatServer { 
    String gonderen1; 
    String alan1; 

    private static final int PORT_NUMBER = 8000; 
    Map<String, List<PrintWriter>> clients; 
    List<PrintWriter> clientwriter; 
    ArrayList<String> liste = new ArrayList<String>(); 

    /** Creates a new server. */ 
    public ChatServer() { 
     clients = new HashMap<String, List<PrintWriter>>(); 
     clientwriter = new LinkedList<PrintWriter>(); 
    } 

    /** Starts the server. */ 
    public void start() { 
     try { 
      ServerSocket s = new ServerSocket(PORT_NUMBER); 
      for (;;) { 
       Socket incoming = s.accept(); 
       new ClientHandler(incoming).start(); 
      } 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
    } 

    /** Adds a new client identified by the given print writer. */ 
    private void addClient(PrintWriter out,String alan) { 
     synchronized(clientwriter) {  
      clientwriter.add(out); 
      clients.put(alan, clientwriter);  
     } 
    } 

    /** Adds the client with given print writer. */ 
    private void removeClient(PrintWriter out) { 
     synchronized(clientwriter) {  
      clientwriter.remove(out); 
      clients.remove(alan1); 
     } 
    } 

    private void broadcast(String msg,String alan) { 
     for(PrintWriter out : clients.get(alan)){ 
      out.println(msg); 
      out.flush(); 
     } 
    } 

    public static void main(String[] args) { 
     if (args.length > 0) { 
      System.out.println(USAGE); 
      System.exit(-1); 
     } 
     new ChatServer().start(); 
    } 

    private class ClientHandler extends Thread { 

     private Socket incoming; 

     public ClientHandler(Socket incoming) { 
      this.incoming = incoming; 
     } 

     public void run() { 
      PrintWriter out = null; 
      try { 
       out = new PrintWriter(
         new OutputStreamWriter(incoming.getOutputStream())); 

       // inform the server of this new client   
       /* ChatServer.this.addClient(out,"mert"); 
       out.print("Welcome to AndyChat! mert"); 
       out.println("Enter BYE to exit."); 
       out.flush();*/ 

       BufferedReader in 
        = new BufferedReader(
         new InputStreamReader(incoming.getInputStream())); 
       String msg; 
       for(;;) { 
        msg = in.readLine(); 
        if(msg!=null){ 
         liste.add(msg); 
         Pattern pat = Pattern.compile("<Gonderen>(.*?)</Gonderen>"); 
         Matcher mat = pat.matcher(msg); 
         if (mat.find()) { 
          gonderen1 = mat.group(1).replaceAll("\\s",""); // => "3" 
          System.out.println("Gonderen "+gonderen1); 
         } 
         Pattern p = Pattern.compile("<Alan>(.*?)</Alan>"); 
         Matcher m = p.matcher(msg); 

         if (m.find()) { 
          alan1 = m.group(1).replaceAll("\\s",""); // => "3"   
          out.print("dsa"); 
          System.out.println("Alanin adi "+alan1); 
         } 
         if(alan1!=null){ 
          System.out.println(clients.get("mert")); 
          ChatServer.this.addClient(out,alan1); 
         } 
        } else {       
         for(int i =0;i<liste.size();i++){ 
         ChatServer.this.broadcast(msg,"mert"); 
         System.out.println("null gelmedi");} 
         break; 
        } 

       } 

       incoming.close(); 
       ChatServer.this.removeClient(out); 
      } catch (Exception e) { 
       if (out != null) { 
        ChatServer.this.removeClient(out); 
       } 
       e.printStackTrace(); 
      } 
     } 
    } 
} 

Answer 1

Matcher mat = pat.matcher(msg);可能給你NullPointerException，如果你傳遞給它一個null味精。

您應該將if(msg==null)支票移至Matcher mat = pat.matcher(msg);之前。

pat.matcher(msg) 
    calls new Matcher (pat, msg) 
    which assigns this.text = msg (which is null) and then calls reset() 
    which calls to = getTextLength() 
    which returns text.length() // which is where the NullPointerException will be 
           // thrown