ribbon的执行原理_2 文章中详细分析了ribbon选择负载均衡器并进行执行的过程，本篇文章就实现自定义服务过滤功能来做详细的分析

场景

1. 灰度和生产的服务都部署在同一个注册中心
2. 生产环境的服务只能调用生产环境的微服务
3. 灰度环境的服务优先调用灰度环境的服务当灰度不存在，则调用生成环境的服务

思路

自定义规则

可从默认的规则ZoneAvoidanceRule入手，因为在生成的时候使用了@ConditionalOnMissingBean说明了可以我们可以自定义Rule

@Bean
@ConditionalOnMissingBean
public IRule ribbonRule(IClientConfig config) {if (this.propertiesFactory.isSet(IRule.class, name)) {return this.propertiesFactory.get(IRule.class, config, name);}ZoneAvoidanceRule rule = new ZoneAvoidanceRule();rule.initWithNiwsConfig(config);return rule;
}

public class ZoneAvoidanceRule extends PredicateBasedRule {private static final Random random = new Random();private CompositePredicate compositePredicate;public ZoneAvoidanceRule() {super();ZoneAvoidancePredicate zonePredicate = new ZoneAvoidancePredicate(this);AvailabilityPredicate availabilityPredicate = new AvailabilityPredicate(this);compositePredicate = createCompositePredicate(zonePredicate, availabilityPredicate);}private CompositePredicate createCompositePredicate(ZoneAvoidancePredicate p1, AvailabilityPredicate p2) {return CompositePredicate.withPredicates(p1, p2).addFallbackPredicate(p2).addFallbackPredicate(AbstractServerPredicate.alwaysTrue()).build();}@Overridepublic void initWithNiwsConfig(IClientConfig clientConfig) {ZoneAvoidancePredicate zonePredicate = new ZoneAvoidancePredicate(this, clientConfig);AvailabilityPredicate availabilityPredicate = new AvailabilityPredicate(this, clientConfig);compositePredicate = createCompositePredicate(zonePredicate, availabilityPredicate);}/*** 被调用的地方是getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);* chooseRoundRobinAfterFiltering(lb.getAllServers(), key)就是真正要过滤逻辑了* */ @Overridepublic AbstractServerPredicate getPredicate() {return compositePredicate;}  /*** 省略部分代码* */  
}

从ZoneAvoidanceRule可以得出以下几点

• 在构造方法中将ZoneAvoidancePredicate和AvailabilityPredicate这两个过滤器通过调用createCompositePredicate方法包装成了compositePredicate组合型过滤器，这三个过滤器在上文有详细解释，这里不再赘述
• createCompositePredicate方法能够将多个过滤器包装进来，然后挨个执行
• 当执行真正的过滤逻辑时也就是getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key)方法，getPredicate()就是要返回这个包装后的组合型过滤器compositePredicate
• 由上可知，我们需要定义一个Rule需要继承PredicateBasedRule，并重写上述几个方法

自定义过滤器

规则分析后，接下来要考虑自定义的过滤器要怎么做，从createCompositePredicate方法入手，其中注入了ZoneAvoidancePredicate，我们可以进行分析，关于这个过滤器的作用已在上一篇文章详细的分析，这里只分析关键部分

public class ZoneAvoidancePredicate extends  AbstractServerPredicate {/*** 省略其余逻辑* */ZoneAvoidancePredicate(IRule rule) {super(rule);}@Overridepublic boolean apply(@Nullable PredicateKey input) {if (!ENABLED.get()) {return true;}String serverZone = input.getServer().getZone();if (serverZone == null) {// there is no zone information from the server, we do not want to filter// out this serverreturn true;}LoadBalancerStats lbStats = getLBStats();if (lbStats == null) {// no stats available, do not filterreturn true;}if (lbStats.getAvailableZones().size() <= 1) {// only one zone is available, do not filterreturn true;}Map<String, ZoneSnapshot> zoneSnapshot = ZoneAvoidanceRule.createSnapshot(lbStats);if (!zoneSnapshot.keySet().contains(serverZone)) {// The server zone is unknown to the load balancer, do not filter it out return true;}logger.debug("Zone snapshots: {}", zoneSnapshot);Set<String> availableZones = ZoneAvoidanceRule.getAvailableZones(zoneSnapshot, triggeringLoad.get(), triggeringBlackoutPercentage.get());logger.debug("Available zones: {}", availableZones);if (availableZones != null) {return availableZones.contains(input.getServer().getZone());} else {return false;}}    
}

• ZoneAvoidancePredicate继承了AbstractServerPredicate实现了apply方法，此方法是真正执行过滤服务实例的逻辑。
• 执行有参构造方法，将rule传给了父类

通过以上分析，我们有了思路来做相应的设计

自定义过滤器逻辑

配置

@ConfigurationProperties("spring.cloud.nacos.discovery.metadata")
@Setter
@Getter
public class ExtraRibbonProperties {private String mark;
}

自动装配配置

@Configuration(proxyBeanMethods = false)
@AutoConfigureBefore(RibbonClientConfiguration.class)
@ConditionalOnProperty(value = "ribbon.filter.metadata.enabled", matchIfMissing = true)
@EnableConfigurationProperties(ExtraRibbonProperties.class)
public class ExtraRibbonAutoConfiguration {@Beanpublic DiscoveryEnabledRule discoveryEnabledRule(ExtraRibbonProperties extraRibbonProperties){return new DiscoveryEnabledRule(extraRibbonProperties);}
}

自定义规则

public class DiscoveryEnabledRule extends PredicateBasedRule {/*** 这里为静态的原因是ribbon在定时任务执行时是直接调用DiscoveryEnabledRule的构造方法，而不是从spring中获得* */private static String mark;private CompositePredicate predicate = null;public DiscoveryEnabledRule(ExtraRibbonProperties extraRibbonProperties){super();mark = extraRibbonProperties.getMark();MetadataAwarePredicate metadataAwarePredicate = new MetadataAwarePredicate(mark, this);Assert.notNull(metadataAwarePredicate, "参数 'abstractServerPredicate' 不能为 null");predicate = createCompositePredicate(metadataAwarePredicate, new AvailabilityPredicate(this, null));}public DiscoveryEnabledRule(){super();MetadataAwarePredicate metadataAwarePredicate = new MetadataAwarePredicate(mark, this);Assert.notNull(metadataAwarePredicate, "参数 'abstractServerPredicate' 不能为 null");predicate = createCompositePredicate(metadataAwarePredicate, new AvailabilityPredicate(this, null));}@Overridepublic AbstractServerPredicate getPredicate() {return predicate;}private CompositePredicate createCompositePredicate(AbstractServerPredicate abstractServerPredicate, AvailabilityPredicate availabilityPredicate) {return CompositePredicate.withPredicates(abstractServerPredicate, availabilityPredicate).build();}
}

自定义过滤器

@Log4j2
public class MetadataAwarePredicate extends AbstractServerPredicate{public static final String MARK_FLAG_TRUE = "true";public static final String MARK_FLAG_FALSE = "false";private static final String MARK_PARAMETER = "mark";private String mark;private DiscoveryEnabledRule discoveryEnabledRule;public MetadataAwarePredicate(String mark,DiscoveryEnabledRule discoveryEnabledRule){super(discoveryEnabledRule);this.mark = mark;this.discoveryEnabledRule = discoveryEnabledRule;}@Overridepublic boolean apply(PredicateKey input) {boolean result = true//这里可以写具体的过滤逻辑return result;}
}