nacos-client 获取配置源码分析

这一篇文章，是介绍获取配置的实现方式。

查看接口com.alibaba.nacos.api.config.ConfigService

/**
     * Get config.
     *
     * @param dataId    dataId
     * @param group     group
     * @param timeoutMs read timeout
     * @return config value
     * @throws NacosException NacosException
     */
    String getConfig(String dataId, String group, long timeoutMs) throws NacosException;

查看接口的实现NacosConfigService

private String getConfigInner(String tenant, String dataId, String group, long timeoutMs) throws NacosException {
        group = null2defaultGroup(group);
        ParamUtils.checkKeyParam(dataId, group);
        ConfigResponse cr = new ConfigResponse();
        
        cr.setDataId(dataId);
        cr.setTenant(tenant);
        cr.setGroup(group);
        
        // Failover是一个宕机文件目录下的本地缓存。没发现有代码会生成这个目录，怀疑是保留功能
        String content = LocalConfigInfoProcessor.getFailover(agent.getName(), dataId, group, tenant);
        if (content != null) {
            LOGGER.warn("[{}] [get-config] get failover ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
                    dataId, group, tenant, ContentUtils.truncateContent(content));
            cr.setContent(content);
            configFilterChainManager.doFilter(null, cr);
            content = cr.getContent();
            return content;
        }
        
        try {
            //去服务端查找配置
            String[] ct = worker.getServerConfig(dataId, group, tenant, timeoutMs);
            cr.setContent(ct[0]);
            //通知过滤器，默认代码没有过滤器，是留给用户实现的。这里目的是将content过滤器转换
            configFilterChainManager.doFilter(null, cr);
            content = cr.getContent();
            
            return content;
        } catch (NacosException ioe) {
            if (NacosException.NO_RIGHT == ioe.getErrCode()) {
                throw ioe;
            }
            LOGGER.warn("[{}] [get-config] get from server error, dataId={}, group={}, tenant={}, msg={}",
                    agent.getName(), dataId, group, tenant, ioe.toString());
        }
        
        LOGGER.warn("[{}] [get-config] get snapshot ok, dataId={}, group={}, tenant={}, config={}", agent.getName(),
                dataId, group, tenant, ContentUtils.truncateContent(content));
        //假如服务端链接异常，使用本地缓存数据
        content = LocalConfigInfoProcessor.getSnapshot(agent.getName(), dataId, group, tenant);
        cr.setContent(content);
        configFilterChainManager.doFilter(null, cr);
        content = cr.getContent();
        return content;
    }

重点看下如何从服务端获取配置worker.getServerConfig(dataId, group, tenant, timeoutMs);

HttpRestResult<String> result = null;
        try {
            Map<String, String> params = new HashMap<String, String>(3);
            if (StringUtils.isBlank(tenant)) {
                params.put("dataId", dataId);
                params.put("group", group);
            } else {
                params.put("dataId", dataId);
                params.put("group", group);
                params.put("tenant", tenant);
            }
            //链接是/v1/cs/configs
            result = agent.httpGet(Constants.CONFIG_CONTROLLER_PATH, null, params, agent.getEncode(), readTimeout);
        } catch (Exception ex) {
            String message = String
                    .format("[%s] [sub-server] get server config exception, dataId=%s, group=%s, tenant=%s",
                            agent.getName(), dataId, group, tenant);
            LOGGER.error(message, ex);
            throw new NacosException(NacosException.SERVER_ERROR, ex);
        }

其实就是发了一个GET请求，把三要素做参数，返回结果。