motan源码分析十：流量切换

motan提供了流量切换的功能，可以实现把一个group的流量切换到另一个group（一个或多个服务都可以）。大家可以使用tomcat部署motan的管理工具，并设置几个组，例如可以参考demo代码：motan_demo_server_commandRegistry.xml。分析源码时可以发现，流量切换是在客户端完成的，与服务端没什么关系，在实际的工作中，可以解决很多问题，例如：某个集群出了问题，可以马上将流量切换到其它集群；在系统升级的过程中，将带升级集群的流量切换到其它集群，实现了24小时随时升级等。

1.motan的流量切换是通过command来实现的，每次我们在motan管理器上进行设置的时候，其实是写入信息到注册中心的command节点，而motan又监听了这些command节点，下面是motan的客户端监听command相关的代码

    protected void subscribeCommand(final URL url, final CommandListener commandListener) {
        try {
            clientLock.lock();//对clientLock进行上锁
            ConcurrentHashMap<CommandListener, IZkDataListener> dataChangeListeners = commandListeners.get(url);//数据变更监听器
            if (dataChangeListeners == null) {
                commandListeners.putIfAbsent(url, new ConcurrentHashMap<CommandListener, IZkDataListener>());
                dataChangeListeners = commandListeners.get(url);
            }
            IZkDataListener zkDataListener = dataChangeListeners.get(commandListener);
            if (zkDataListener == null) {
                dataChangeListeners.putIfAbsent(commandListener, new IZkDataListener() {//增加新的listener
                    @Override
                    public void handleDataChange(String dataPath, Object data) throws Exception {
                        commandListener.notifyCommand(url, (String) data);//调用commandListener的notifyCommand方法
                        LoggerUtil.info(String.format("[ZookeeperRegistry] command data change: path=%s, command=%s", dataPath, (String) data));
                    }

                    @Override
                    public void handleDataDeleted(String dataPath) throws Exception {
                        commandListener.notifyCommand(url, null);
                        LoggerUtil.info(String.format("[ZookeeperRegistry] command deleted: path=%s", dataPath));
                    }
                });
                zkDataListener = dataChangeListeners.get(commandListener);
            }

            String commandPath = ZkUtils.toCommandPath(url);
            zkClient.subscribeDataChanges(commandPath, zkDataListener);//向zookeeper注册监听事件
            LoggerUtil.info(String.format("[ZookeeperRegistry] subscribe command: path=%s, info=%s", commandPath, url.toFullStr()));
        } catch (Throwable e) {
            throw new MotanFrameworkException(String.format("Failed to subscribe %s to zookeeper(%s), cause: %s", url, getUrl(), e.getMessage()), e);
        } finally {
            clientLock.unlock();
        }
    }

2.CommandServiceManager实现了上节中的commandListener

    public void notifyCommand(URL serviceUrl, String commandString) {
        LoggerUtil.info("CommandServiceManager notify command. service:" + serviceUrl.toSimpleString() + ", command:" + commandString);

        if (!MotanSwitcherUtil.isOpen(MOTAN_COMMAND_SWITCHER) || commandString == null) {//判断命令开关是否打开
            LoggerUtil.info("command reset empty since swither is close.");
            commandString = "";
        }

        List<URL> finalResult = new ArrayList<URL>();
        URL urlCopy = serviceUrl.createCopy();//serviceurl的副本

        if (!StringUtils.equals(commandString, commandStringCache)) {
            commandStringCache = commandString;
            commandCache = RpcCommandUtil.stringToCommand(commandStringCache);//将字符串转换为命令
            Map<String, Integer> weights = new HashMap<String, Integer>();

            if (commandCache != null) {
                commandCache.sort();
                finalResult = discoverServiceWithCommand(refUrl, weights, commandCache);
            } else {
                // 如果是指令有异常时，应当按没有指令处理，防止错误指令导致服务异常
                if (StringUtils.isNotBlank(commandString)) {
                    LoggerUtil.warn("command parse fail, ignored! command:" + commandString);
                    commandString = "";
                }
                // 没有命令时，只返回这个manager实际group对应的结果
                finalResult.addAll(discoverOneGroup(refUrl));

            }

            // 指令变化时，删除不再有效的缓存，取消订阅不再有效的group
            Set<String> groupKeys = groupServiceCache.keySet();
            for (String gk : groupKeys) {
                if (!weights.containsKey(gk)) {
                    groupServiceCache.remove(gk);
                    URL urlTemp = urlCopy.createCopy();
                    urlTemp.addParameter(URLParamType.group.getName(), gk);
                    registry.unsubscribeService(urlTemp, this);
                }
            }
        } else {
            LoggerUtil.info("command not change. url:" + serviceUrl.toSimpleString());
            // 指令没有变化，什么也不做
            return;
        }

        for (NotifyListener notifyListener : notifySet) {
            notifyListener.notify(registry.getUrl(), finalResult);
        }

        // 当指令从有改到无时，会触发取消订阅所有的group，需要重新订阅本组的service
        if ("".equals(commandString)) {
            LoggerUtil.info("reSub service" + refUrl.toSimpleString());
            registry.subscribeService(refUrl, this);
        }
    }

3.discoverServiceWithCommand的相关代码

    public List<URL> discoverServiceWithCommand(URL serviceUrl, Map<String, Integer> weights, RpcCommand rpcCommand, String localIP) {
        if (rpcCommand == null || CollectionUtil.isEmpty(rpcCommand.getClientCommandList())) {
            return discoverOneGroup(serviceUrl);
        }

        List<URL> mergedResult = new LinkedList<URL>();
        String path = serviceUrl.getPath();//获取路径

        List<RpcCommand.ClientCommand> clientCommandList = rpcCommand.getClientCommandList();
        boolean hit = false;
        for (RpcCommand.ClientCommand command : clientCommandList) {
            mergedResult = new LinkedList<URL>();
            // 判断当前url是否符合过滤条件
            boolean match = RpcCommandUtil.match(command.getPattern(), path);
            if (match) {
                hit = true;
                if (!CollectionUtil.isEmpty(command.getMergeGroups())) {
                    // 计算出所有要合并的分组及权重
                    try {
                        buildWeightsMap(weights, command);
                    } catch (MotanFrameworkException e) {
                        LoggerUtil.warn("build weights map fail!" + e.getMessage());
                        continue;
                    }
                    // 根据计算结果，分别发现各个group的service，合并结果
                    mergedResult.addAll(mergeResult(serviceUrl, weights));
                } else {
                    mergedResult.addAll(discoverOneGroup(serviceUrl));
                }

                LoggerUtil.info("mergedResult: size-" + mergedResult.size() + " --- " + mergedResult.toString());

                if (!CollectionUtil.isEmpty(command.getRouteRules())) {
                    LoggerUtil.info("router: " + command.getRouteRules().toString());

                    for (String routeRule : command.getRouteRules()) {
                        String[] fromTo = routeRule.replaceAll("\s+", "").split("to");

                        if (fromTo.length != 2) {
                            routeRuleConfigError();
                            continue;
                        }
                        String from = fromTo[0];
                        String to = fromTo[1];
                        if (from.length() < 1 || to.length() < 1 || !IP_PATTERN.matcher(from).find() || !IP_PATTERN.matcher(to).find()) {
                            routeRuleConfigError();
                            continue;
                        }
                        boolean oppositeFrom = from.startsWith("!");
                        boolean oppositeTo = to.startsWith("!");
                        if (oppositeFrom) {
                            from = from.substring(1);
                        }
                        if (oppositeTo) {
                            to = to.substring(1);
                        }
                        int idx = from.indexOf('*');
                        boolean matchFrom;
                        if (idx != -1) {
                            matchFrom = localIP.startsWith(from.substring(0, idx));
                        } else {
                            matchFrom = localIP.equals(from);
                        }

                        // 开头有!，取反
                        if (oppositeFrom) {
                            matchFrom = !matchFrom;
                        }
                        LoggerUtil.info("matchFrom: " + matchFrom + ", localip:" + localIP + ", from:" + from);
                        if (matchFrom) {
                            boolean matchTo;
                            Iterator<URL> iterator = mergedResult.iterator();
                            while (iterator.hasNext()) {
                                URL url = iterator.next();
                                if (url.getProtocol().equalsIgnoreCase("rule")) {
                                    continue;
                                }
                                idx = to.indexOf('*');
                                if (idx != -1) {
                                    matchTo = url.getHost().startsWith(to.substring(0, idx));
                                } else {
                                    matchTo = url.getHost().equals(to);
                                }
                                if (oppositeTo) {
                                    matchTo = !matchTo;
                                }
                                if (!matchTo) {
                                    iterator.remove();
                                    LoggerUtil.info("router To not match. url remove : " + url.toSimpleString());
                                }
                            }
                        }
                    }
                }
                // 只取第一个匹配的 TODO 考虑是否能满足绝大多数场景需求
                break;
            }
        }

        List<URL> finalResult = new ArrayList<URL>();
        if (!hit) {
            finalResult = discoverOneGroup(serviceUrl);
        } else {
            finalResult.addAll(mergedResult);
        }
        return finalResult;
    }