没有发送数据时Java ServerSocket异常

Question

我有一个简单的Daemon设置，带有一个监听数据包的ServerSocket，当建立连接并发送数据时，一切正常，但是当建立连接并且不发送数据时，程序因异常而崩溃。以下是Listener 线程的代码。

public class Listener implements Runnable {
    ServerSocket listenerSocket;
    Socket connection = null;
    OutputStream out;
    BufferedReader in;
    String packet;
    Console console;
    public Listener(Console Console){
        console = Console;

    }
    @Override
    public void run()
    {
        try{
            listenerSocket = new ServerSocket(5344); //General socket setup
            console.write("INFO", "Listener started");
            do{
            connection = listenerSocket.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            DataOutputStream out = new DataOutputStream(connection.getOutputStream()); 
                try{
                    packet = (String)in.readLine(); // Get packet data
                    if(packet != null){
                        byte[] decoded = Base64.decodeBase64(packet);
                        packet = new String(decoded, "UTF-8");
                        Thread handler = new Thread(new Handler(packet, out, console, in, connection)); // Handler class will take / parse packet data
                        handler.start();
                    }
                }
                catch(Exception e){
                    e.printStackTrace();
                }
            }while(!packet.equals("shutdown"));
        }
        catch(IOException ioException){
            ioException.printStackTrace();
        }
        finally{
            try{
                in.close();
                out.close();
                listenerSocket.close();
            }
            catch(IOException ioException){
                ioException.printStackTrace();
            }
        }
    }
}

这是建立连接但未发送数据时的错误:

Exception in thread "Thread-0" java.lang.NullPointerException
        at com.cj.panel.Listener.run(Listener.java:53)
        at java.lang.Thread.run(Thread.java:744)

第 53 行是 in.close();

Answer 1

上述问题最简单的解决方案之一是......只需在finally block 中放置一个空检查

finally
{
   if(in!=null)
     in.close();

   if(out!=null)
     out.close();
}