socket编程读取输入流的疑惑解决思路

socket编程读取输入流的疑惑
服务器获取客户端信息的代码大致如下
InputStream is = socket.getInputStream();
byte[] buffer = new byte[1024];
int length = is.read(buffer);
String msg = new String(buffer,0,length);

为什么以下的写法是错误的
InputStream is = socket.getInputStream();
byte[] buffer = new byte[1024];
int length = 0;
while((length = is.read(buffer)) != -1){
  String msg = new String(buffer,0,length);
}

------解决方案--------------------
我之前这样也不行，不知道是为什么！等待求解啊！！！