code: public HttpConnection header(String header, String value, boolean isOverride) {
  		if (null != this.conn) {
  			if (isOverride) {
  				this.conn.setRequestProperty(header, value);
  			} else {
  				this.conn.addRequestProperty(header, value);
  			}
  		}
  
  		return this;
  	}
docs: 设置请求头<br>
  当请求头存在时，覆盖之
  
  @param header 头名
  @param value 头值
  @param isOverride 是否覆盖旧值
  @return HttpConnection