private static void writeString(DataOutputStream dous,int len,String s)
	throws IOException{
		byte[] data=s.getBytes();
		if(data.length>len){
			throw new IOException("д볤Ϊ"+data.length+",!");
		}
		dous.write(data);
		 while(len>data.length){//̣Ҫ0
			 dous.writeByte('\0');//0
			 len--;
		 }
	}