Nacos深入浅出（五）

四中标色的代码

          result = ConfigService.dump(dataId, group, tenant, cf.getContent(), lastModified);

我们看下这个方法

  /**
     * 保存配置文件，并缓存md5.
     */
    static public boolean dump(String dataId, String group, String tenant, String content, long lastModifiedTs) {
        String groupKey = GroupKey2.getKey(dataId, group, tenant);
        makeSure(groupKey);
        final int lockResult = tryWriteLock(groupKey);
        assert (lockResult != 0);

        if (lockResult < 0) {
            dumpLog.warn("[dump-error] write lock failed. {}", groupKey);
            return false;
        }

        try {
            final String md5 = MD5.getInstance().getMD5String(content);
            if (md5.equals(ConfigService.getContentMd5(groupKey))) {
                dumpLog.warn(
                    "[dump-ignore] ignore to save cache file. groupKey={}, md5={}, lastModifiedOld={}, "
                        + "lastModifiedNew={}",
                    groupKey, md5, ConfigService.getLastModifiedTs(groupKey), lastModifiedTs);
            } else if (!STANDALONE_MODE || PropertyUtil.isStandaloneUseMysql()) {
                DiskUtil.saveToDisk(dataId, group, tenant, content);
            }
            updateMd5(groupKey, md5, lastModifiedTs);
            return true;
        } catch (IOException ioe) {
            dumpLog.error("[dump-exception] save disk error. " + groupKey + ", " + ioe.toString(), ioe);
            if (ioe.getMessage() != null) {
                String errMsg = ioe.getMessage();
                if (NO_SPACE_CN.equals(errMsg) || NO_SPACE_EN.equals(errMsg) || errMsg.contains(DISK_QUATA_CN)
                    || errMsg.contains(DISK_QUATA_EN)) {
                    // 磁盘写满保护代码
                    fatalLog.error("磁盘满自杀退出", ioe);
                    System.exit(0);
                }
            }
            return false;
        } finally {
            releaseWriteLock(groupKey);
        }
    }

这里MD5加密的意义就体现出来了，如果content的值没有变，这不需要激活

LocalDataChangeEvent，不然则激活，这里又是另一个天地了；也是我们感兴趣的地方，go!

 public static void updateMd5(String groupKey, String md5, long lastModifiedTs) {
        CacheItem cache = makeSure(groupKey);
        if (cache.md5 == null || !cache.md5.equals(md5)) {
            cache.md5 = md5;
            cache.lastModifiedTs = lastModifiedTs;
            EventDispatcher.fireEvent(new LocalDataChangeEvent(groupKey));
        }
    }

这个LocalDataChangeEvent比较简单，大家简单的过下，

public class LocalDataChangeEvent implements Event {
    final public String groupKey;
    final public boolean isBeta;
    final public List<String> betaIps;
    final public String tag;

    public LocalDataChangeEvent(String groupKey) {
        this.groupKey = groupKey;
        this.isBeta = false;
        this.betaIps = null;
        this.tag = null;
    }

    public LocalDataChangeEvent(String groupKey, boolean isBeta, List<String> betaIps) {
        this.groupKey = groupKey;
        this.isBeta = isBeta;
        this.betaIps = betaIps;
        this.tag = null;
    }

    public LocalDataChangeEvent(String groupKey, boolean isBeta, List<String> betaIps, String tag) {
        this.groupKey = groupKey;
        this.isBeta = isBeta;
        this.betaIps = betaIps;
        this.tag = tag;
    }
}

我们主要看这个fireEvent里面的这个onEvent是如何处理的，上代码

LongPollingService.java

 @Override
    public void onEvent(Event event) {
        if (isFixedPolling()) {
            // ignore
        } else {
            if (event instanceof LocalDataChangeEvent) {
                LocalDataChangeEvent evt = (LocalDataChangeEvent)event;
                scheduler.execute(new DataChangeTask(evt.groupKey, evt.isBeta, evt.betaIps));
            }
        }
    }

DataChangeTask这个类，看看他的庐山真面目！

 class DataChangeTask implements Runnable {
        @Override
        public void run() {
            try {
                ConfigService.getContentBetaMd5(groupKey);
                for (Iterator<ClientLongPolling> iter = allSubs.iterator(); iter.hasNext(); ) {
                    ClientLongPolling clientSub = iter.next();
                    if (clientSub.clientMd5Map.containsKey(groupKey)) {
                        // 如果beta发布且不在beta列表直接跳过
                        if (isBeta && !betaIps.contains(clientSub.ip)) {
                            continue;
                        }

                        // 如果tag发布且不在tag列表直接跳过
                        if (StringUtils.isNotBlank(tag) && !tag.equals(clientSub.tag)) {
                            continue;
                        }

                        getRetainIps().put(clientSub.ip, System.currentTimeMillis());
                        iter.remove(); // 删除订阅关系
                        LogUtil.clientLog.info("{}|{}|{}|{}|{}|{}|{}",
                            (System.currentTimeMillis() - changeTime),
                            "in-advance",
                            RequestUtil.getRemoteIp((HttpServletRequest)clientSub.asyncContext.getRequest()),
                            "polling",
                            clientSub.clientMd5Map.size(), clientSub.probeRequestSize, groupKey);
                        clientSub.sendResponse(Arrays.asList(groupKey));
                    }
                }
            } catch (Throwable t) {
                LogUtil.defaultLog.error("data change error:" + t.getMessage(), t.getCause());
            }
        }

        DataChangeTask(String groupKey) {
            this(groupKey, false, null);
        }

        DataChangeTask(String groupKey, boolean isBeta, List<String> betaIps) {
            this(groupKey, isBeta, betaIps, null);
        }

        DataChangeTask(String groupKey, boolean isBeta, List<String> betaIps, String tag) {
            this.groupKey = groupKey;
            this.isBeta = isBeta;
            this.betaIps = betaIps;
            this.tag = tag;
        }

        final String groupKey;
        final long changeTime = System.currentTimeMillis();
        final boolean isBeta;
        final List<String> betaIps;
        final String tag;
    }

到这里感觉好像还是没看到究竟是在哪变了，奇怪哦，咱们继续想办法，既然跟代码没跟出什么名堂，我不妨停下来想想？

1、client在请求处理nacos参数的时候调用什么rpc服务，用的是返回的value么？

2、如果没有请求的话 数据无非就几种载体，DB，cache,file

DB不可能，我们的业务库根本就没有创建过相应的存储表，所以pass;

cache也不可能，我们重启服务之后，数据还是在的，所以呢，肯定就是file了，会不会像我们的property一样，存在某个地方，然后按照一定的规则去取值，

是不是？继续往下走,goo!