public void setConnNum(int connNum) {
        if (connNum <= 0 || connNum > Configs.MAX_CONN_NUM_PER_URL) {
            throw new IllegalArgumentException("Illegal value of connection number [" + connNum
                                               + "], must be an integer between ["
                                               + Configs.DEFAULT_CONN_NUM_PER_URL + ", "
                                               + Configs.MAX_CONN_NUM_PER_URL + "].");
        }
        this.connNum = connNum;
    }
Get property value according to property key

@param key property key
@return property value
src/main/java/com/alipay/remoting/Url.java