java网络套接字服务端读取字节数为0

客户端采用的是阻塞io，服务器采用的是nio，客户端向服务器发送了一个字符串，服务端这边读取字节数始终为0，我猜想有可能是未读取完整，使用了while循环反复读取仍然是0，这是为什么呢？有没什么办法解决呢？求大神指导客户端代码public class Tst {
public static void main(String[] args){
try {
Socket socket=new Socket("127.0.0.1",9999);
String[] strs={new String("str1\r\n"),
new String("str2\r\n"),
new String("str3\r\n")};
OutputStream out=socket.getOutputStream();
int i=0;
while(i<3){
try {

Thread.sleep(3000);
System.out.println("准备发送！");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
out.write(strs[i].getBytes());
out.flush();

i++;
}
if(out!=null){
out.close();
}

socket.close();


} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}


}
}服务器代码public class TstServer {    private Selector selector = null;
    static final int port = 9999;
    private Charset charset = Charset.forName("UTF-8");
    
    
    public void init() throws IOException
    {
        selector = Selector.open();
        ServerSocketChannel server = ServerSocketChannel.open();
        server.bind(new InetSocketAddress(port));
        server.configureBlocking(false);
        server.register(selector, SelectionKey.OP_ACCEPT); 
        
        
        while(true) {
            int readyChannels = selector.select();
            if(readyChannels == 0) continue; 
            Set selectedKeys = selector.selectedKeys(); 
            Iterator keyIterator = selectedKeys.iterator();
            while(keyIterator.hasNext()) {
                 SelectionKey sk = (SelectionKey) keyIterator.next();
                 keyIterator.remove();
                 dealWithSelectionKey(server,sk);
            }
        }
    }
    
    public void dealWithSelectionKey(ServerSocketChannel server,SelectionKey sk) throws IOException {
        if(sk.isAcceptable())
        {
            SocketChannel sc = server.accept();
            sc.configureBlocking(false);
            sc.register(selector, SelectionKey.OP_READ);
            sk.interestOps(SelectionKey.OP_ACCEPT);
            System.out.println("连接请求来自 :" + sc.getRemoteAddress());
        }
        //处理来自客户端的数据读取请求
        if(sk.isReadable())
        {
            SocketChannel sc = (SocketChannel)sk.channel(); 
            ByteBuffer buff = ByteBuffer.allocate(1024);
            StringBuilder content = new StringBuilder();
            try
            {
             int length=0;
                while(true)
                {
                 System.out.println("接收了一次, 大小为" + length);
                    buff.flip();
                    content.append(charset.decode(buff));
                    
                    length=sc.read(buff);
                    if(length==0){
                     try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
                    }
                    if(buff.toString().endsWith("\r\n")) break;
                    
                }
                System.out.println("Server is listening from client " + sc.getRemoteAddress() + " data rev is: " + content);
                sk.interestOps(SelectionKey.OP_READ);
            }
            catch (IOException io)
            {
                sk.cancel();
                if(sk.channel() != null)
                {
                    sk.channel().close();
                }
            }
           
            
        }
    }
    
    public static void main(String[] args) throws IOException 
    {
        new TstServer().init();
    }
}