Socket阻塞问题

[幻想波普星]

客户端代码如下：

public class Client {
	public static void main(String[] args) throws UnknownHostException, IOException, InterruptedException {
		Socket client=new Socket("localhost", 7978);
		BufferedReader br=new BufferedReader(new InputStreamReader(client.getInputStream()));
		PrintWriter pw=new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
		//pw.println("wefwfwf");
		//pw.flush();
		String da=null;
		while((da=br.readLine())!=null) {
			System.out.println(da);
		}	
	}
}

服务器代码如下：

public class Server implements Runnable{
	private static ServerSocket serverSocket;
	private static List<Socket> clients;
	private static PrintWriter pw;
	private static String msg;
	private BufferedReader br;
	private static List<String> msgs;
	public  Server() throws IOException {
		clients=new ArrayList<>();;
		serverSocket=new ServerSocket(7978);
		msgs=new ArrayList<>();
		msg=null;
	}
	@Override
	public void run() {
		try {		
			while(true) {
		//	System.out.println("");   必须加这个？？？
				if(clients.size()!=0) {
					if(msgs.size()!=0) {
						for(Socket client:clients) {
							pw=new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
							pw.println(msgs.get(0));
							pw.flush();
						}
						msgs.remove(0);
					}
				}
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	public static void main(String[] args) throws IOException {
			new Thread(new Server()).start();
			while(true) {
				Socket client=serverSocket.accept();
				msg=client.toString()+"is coming";
				msgs.add(msg);
				clients.add(client); 				
			}		
	}
}

写了一个小的socket多线程通信demo，可以看到我注释的那个地方，为什么必须加一个这个东西，不然就阻塞了。讲道理我的PrintWrirter用的是println啊，不应该存在回车的问题的，死活想不明白，请大神执教

[幻想波普星]

已经解决，ArrayList线程不安全导致的，换成Vector

[静看星辰变]

println就是会输出一个回车啊，不输出回车用print