为什么它返回空指针异常(服务器端)

时间:2010-01-18 18:25:30

标签: java networking

这是我的服务器类,它允许客户端相互聊天,但它会返回此行的nullpointer异常:while (!(line = in.readLine()).equalsIgnoreCase("/quit"))你能帮助我吗?谢谢。

我的ChatHandler类:

 final static Vector handlers = new Vector(10);
private Socket socket;
private BufferedReader in;
private PrintWriter out;

public ChatHandler(Socket socket) throws IOException {
    this.socket = socket;
    in = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));
    out = new PrintWriter(
            new OutputStreamWriter(socket.getOutputStream()));
}

@Override
public void run() {
    String line;

    synchronized (handlers) {
        handlers.addElement(this);
    // add() not found in Vector class
    }
    try {
        while (!(line = in.readLine()).equalsIgnoreCase("/quit")) {
            for (int i = 0; i < handlers.size(); i++) {
                synchronized (handlers) {
                    ChatHandler handler =
                            (ChatHandler) handlers.elementAt(i);
                    handler.out.println(line + "\r");
                    handler.out.flush();
                }
            }
        }
    } catch (IOException ioe) {
        ioe.printStackTrace();
    } finally {
        try {
            in.close();
            out.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            synchronized (handlers) {
                handlers.removeElement(this);
            }
        }
    }
}

客户端类的一部分:

  String teXt = MainClient.getText();

    os.println(teXt);
    os.flush();
    try {
        String line = is.readLine();



            setFromServertext("Text recieved:"+line+"\n");

        is.close();
        is.close();
        c.close();
    } catch (IOException ex) {
        Logger.getLogger(MainClient.class.getName()).log(Level.SEVERE, null, ex);
    }

2 个答案:

答案 0 :(得分:3)

这不是正确的习惯用法。当到达流的末尾时,BufferedReader#readLine()将返回null

因此,以下

while (!(line = in.readLine()).equalsIgnoreCase("/quit")) {
    // Do stuff.
}

必须替换为:

while ((line = in.readLine()) != null && !line.equalsIgnoreCase("/quit")) {
    // Do stuff.
}

另请参阅Sun自己的基本Java IO教程,了解如何使用BufferedReaderhttp://java.sun.com/docs/books/tutorial/essential/io/

答案 1 :(得分:2)

当没有其他内容可供阅读时,

in.readLine()将返回null。您需要将其更改为

String line;
while ((line = in.readLine()) != null) {
    if (!line.equalsIgnoreCase("/quit")) {

    }
}