code: public static long copy(Reader reader, Writer writer) throws IORuntimeException {
  		return copy(reader, writer, DEFAULT_BUFFER_SIZE);
  	}
docs: 将Reader中的内容复制到Writer中 使用默认缓存大小
  
  @param reader Reader
  @param writer Writer
  @return 拷贝的字节数
  @throws IORuntimeException IO异常