BufferedReader.readLine（）不读取并挂起系统（等待）

BufferedReader.readLine（）不读取并挂起系统（等待）。

InputStream istrm = runtimeProcess.getInputStream();
InputStreamReader istrmrdr = new InputStreamReader(istrm);
BufferedReader buffrdr = new BufferedReader(istrmrdr);
System.out.println("4");
String data;
String st;
System.out.println("4a");
while (!(st=buffrdr.readLine()).isEmpty()) {
    System.out.println("5 in loop");
}