上一章我们分析了客户端调用服务端相关的源码，但是到了cluster里面的部分我们就没有分析了，本章将深入分析cluster和它的相关支持类。

1.clustersupport的创建过程，上一章的ReferConfig的initRef()方法中调用了相关的创建代码：

for(Iterator iterator = protocols.iterator(); iterator.hasNext();)        {            ProtocolConfig protocol = (ProtocolConfig)iterator.next();            LoggerUtil.info((new StringBuilder("ProtocolConfig's")).append(protocol.getName()).toString());            Map params = new HashMap();            params.put(URLParamType.nodeType.getName(), "referer");            params.put(URLParamType.version.getName(), URLParamType.version.getValue());            params.put(URLParamType.refreshTimestamp.getName(), String.valueOf(System.currentTimeMillis()));            collectConfigParams(params, new AbstractConfig[] {                protocol, basicReferer, extConfig, this            });            collectMethodConfigParams(params, getMethods());            URL refUrl = new URL(protocol.getName(), localIp, 0, interfaceClass.getName(), params);            ClusterSupport clusterSupport = createClusterSupport(refUrl, configHandler, registryUrls);//创建clustersupport            clusterSupports.add(clusterSupport);            clusters.add(clusterSupport.getCluster());//获取对应的cluster            proxy = proxy != null ? proxy : refUrl.getParameter(URLParamType.proxy.getName(), URLParamType.proxy.getValue());        }    private ClusterSupport createClusterSupport(URL refUrl, ConfigHandler configHandler, List registryUrls)    {        List regUrls = new ArrayList();        if(StringUtils.isNotBlank(directUrl) || "injvm".equals(refUrl.getProtocol()))        {            URL regUrl = new URL("local", "127.0.0.1", 0, com/weibo/api/motan/registry/RegistryService.getName());            if(StringUtils.isNotBlank(directUrl))            {                StringBuilder duBuf = new StringBuilder(128);                String dus[] = MotanConstants.COMMA_SPLIT_PATTERN.split(directUrl);                String as[];                int j = (as = dus).length;                for(int i = 0; i < j; i++)                {                    String du = as[i];                    if(du.contains(":"))                    {                        String hostPort[] = du.split(":");                        URL durl = refUrl.createCopy();                        durl.setHost(hostPort[0].trim());                        durl.setPort(Integer.parseInt(hostPort[1].trim()));                        durl.addParameter(URLParamType.nodeType.getName(), "service");                        duBuf.append(StringTools.urlEncode(durl.toFullStr())).append(",");                    }                }                if(duBuf.length() > 0)                {                    duBuf.deleteCharAt(duBuf.length() - 1);                    regUrl.addParameter(URLParamType.directUrl.getName(), duBuf.toString());                }            }            regUrls.add(regUrl);        } else//走注册中心的方式        {            if(registryUrls == null || registryUrls.isEmpty())                throw new IllegalStateException(String.format("No registry to reference %s on the consumer %s , please config 
      in your spring config.", new Object[] {                    interfaceClass, "127.0.0.1"                }));            URL url;            for(Iterator iterator = registryUrls.iterator(); iterator.hasNext(); regUrls.add(url.createCopy()))                url = (URL)iterator.next();        }        URL url;        for(Iterator iterator1 = regUrls.iterator(); iterator1.hasNext(); url.addParameter(URLParamType.embed.getName(), StringTools.urlEncode(refUrl.toFullStr())))            url = (URL)iterator1.next();        return configHandler.buildClusterSupport(interfaceClass, regUrls);//调用simpleconfighandler的创建clustersupport方法    }    public 
     
       ClusterSupport
      
        buildClusterSupport(Class
       
         interfaceClass, List
        
          registryUrls) {        ClusterSupport
         
           clusterSupport = new ClusterSupport
          
           (interfaceClass, registryUrls);//创建cluster支持类，将业务接口和注册中心信息传递进去 clusterSupport.init();//初始化 return clusterSupport; }
          
         
        
       
      
     

2.clustersupport的init和prepare方法

public void init() {        prepareCluster();        URL subUrl = toSubscribeUrl(url);        for (URL ru : registryUrls) {//循环注册中心的url            String directUrlStr = ru.getParameter(URLParamType.directUrl.getName());            // 如果有directUrl，直接使用这些directUrls进行初始化，不用到注册中心discover            if (StringUtils.isNotBlank(directUrlStr)) {                List
     
       directUrls = parseDirectUrls(directUrlStr);                if (!directUrls.isEmpty()) {                    notify(ru, directUrls);                    LoggerUtil.info("Use direct urls, refUrl={}, directUrls={}", url, directUrls);                    continue;                }            }            // client 注册自己，同时订阅service列表            Registry registry = getRegistry(ru);//获取zookeeper的注册中心            registry.subscribe(subUrl, this);//注册自己并订阅服务        }        boolean check = Boolean.parseBoolean(url.getParameter(URLParamType.check.getName(), URLParamType.check.getValue()));        if (!CollectionUtil.isEmpty(cluster.getReferers()) || !check) {            cluster.init();//初始化集群            if (CollectionUtil.isEmpty(cluster.getReferers()) && !check) {                LoggerUtil.warn(String.format("refer:%s", this.url.getPath() + "/" + this.url.getVersion()), "No services");            }            return;        }        throw new MotanFrameworkException(String.format("ClusterSupport No service urls for the refer:%s, registries:%s",                this.url.getIdentity(), registryUrls), MotanErrorMsgConstant.SERVICE_UNFOUND);    }    private void prepareCluster() {        String clusterName = url.getParameter(URLParamType.cluster.getName(), URLParamType.cluster.getValue());//集群名称        String loadbalanceName = url.getParameter(URLParamType.loadbalance.getName(), URLParamType.loadbalance.getValue());//负载均衡名称        String haStrategyName = url.getParameter(URLParamType.haStrategy.getName(), URLParamType.haStrategy.getValue());//ha高可用名称        cluster = ExtensionLoader.getExtensionLoader(Cluster.class).getExtension(clusterName);//获取具体的集群对象        LoadBalance
      
        loadBalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(loadbalanceName);//获取具体的负载均衡方式，目前motan支持6种负载方式        HaStrategy
       
         ha = ExtensionLoader.getExtensionLoader(HaStrategy.class).getExtension(haStrategyName);//获取高可用的方式，目前支持两种failfast和failover方式        cluster.setLoadBalance(loadBalance);        cluster.setHaStrategy(ha);        cluster.setUrl(url);    }
       
      
     

3.负载均衡，motan支持6种方式，分别是：轮训、随机、hash、本地服务优先、权重可配置、低并发优先，具体代码可见com.weibo.api.motan.cluster.loadbalance目录，本文我们主要看一下轮训的方式：

public class RoundRobinLoadBalance
     
       extends AbstractLoadBalance
      
        {    private AtomicInteger idx = new AtomicInteger(0);    @Override    protected Referer
       
         doSelect(Request request) {        List
        
         
          > referers = getReferers();//获取所有服务器的引用        int index = idx.incrementAndGet();//自增        for (int i = 0; i < referers.size(); i++) {            Referer
          
            ref = referers.get((i + index) % referers.size());//利用自增数去模，达到轮训的目的 if (ref.isAvailable()) { return ref; } } return null; } @Override protected void doSelectToHolder(Request request, List
           
            
             > refersHolder) { List
             
              
               > referers = getReferers(); int index = idx.incrementAndGet(); for (int i = 0; i < referers.size(); i++) { Referer
               
                 referer = referers.get((i + index) % referers.size()); if (referer.isAvailable()) { refersHolder.add(referer); } } }}
               
              
             
            
           
          
         
        
       
      
     

4.motan支持failfast和failover两种方式，failfast只调用一次，如果失败则直接返回失败，failover循环调用若干次，直到成功或循环结束后

public Response call(Request request, LoadBalance
     
       loadBalance) {        List
      
       
        > referers = selectReferers(request, loadBalance);//获取所有的引用        if (referers.isEmpty()) {            throw new MotanServiceException(String.format("FailoverHaStrategy No referers for request:%s, loadbalance:%s", request,                    loadBalance));        }        URL refUrl = referers.get(0).getUrl();        // 先使用method的配置        int tryCount =                refUrl.getMethodParameter(request.getMethodName(), request.getParamtersDesc(), URLParamType.retries.getName(),                        URLParamType.retries.getIntValue());//获取重试次数        // 如果有问题，则设置为不重试        if (tryCount < 0) {            tryCount = 0;        }        for (int i = 0; i <= tryCount; i++) {            Referer
        
          refer = referers.get(i % referers.size());//循环调用            try {                request.setRetries(i);                return refer.call(request);            } catch (RuntimeException e) {                // 对于业务异常，直接抛出                if (ExceptionUtil.isBizException(e)) {                    throw e;//业务异常退出调用                } else if (i >= tryCount) {                    throw e;                }                LoggerUtil.warn(String.format("FailoverHaStrategy Call false for request:%s error=%s", request, e.getMessage()));            }        }        throw new MotanFrameworkException("FailoverHaStrategy.call should not come here!");    }
        
       
      
     

本章知识点总结：

1.一个cluster有一个cluster的支持类，有一个ha，有一个loadbalance;

2.motan支持6种负载均衡方式；

3.motan支持failover的ha方式；