一 类图中的位置
二 ClientConfigEnabledRoundRobinRule代码解读
//该策略较为特殊,我们一般不直接使用它。因为它本身并没有实现什么特殊的处理逻辑。
//通过继承该策略,默认的choose就实现了线性轮询机制,在子类中做一些高级策略时通常可能存在
//一些无法实施的情况,就可以用父类的实现作为备选。
public class ClientConfigEnabledRoundRobinRule extends AbstractLoadBalancerRule {
//内部定义了一个RoundRobinRule策略
RoundRobinRule roundRobinRule = new RoundRobinRule();
@Override
public void initWithNiwsConfig(IClientConfig clientConfig) {
roundRobinRule = new RoundRobinRule();
}
@Override
public void setLoadBalancer(ILoadBalancer lb) {
super.setLoadBalancer(lb);
roundRobinRule.setLoadBalancer(lb);
}
//使用RoundRobinRule的线性轮询机制
@Override
public Server choose(Object key) {
if (roundRobinRule != null) {
return roundRobinRule.choose(key);
} else {
throw new IllegalArgumentException(
"This class has not been initialized with the RoundRobinRule class");
}
}
}
三 BestAvailableRule 代码解读
//继承自ClientConfigEnabledRoundRobinRule
//该策略的特性是可选出最空闲的实例
public class BestAvailableRule extends ClientConfigEnabledRoundRobinRule {
//注入负载均衡器的统计对象loadBalancerStats
private LoadBalancerStats loadBalancerStats;
@Override
public Server choose(Object key) {
//当loadBalancerStats为空,采用父类的线性轮询
//体现了在ClientConfigEnabledRoundRobinRule的子类无法满足高级策略时,采用
//ClientConfigEnabledRoundRobinRule的线性轮询特性
if (loadBalancerStats == null) {
return super.choose(key);
}
List<Server> serverList = getLoadBalancer().getAllServers();
int minimalConcurrentConnections = Integer.MAX_VALUE;
long currentTime = System.currentTimeMillis();
Server chosen = null;
//利用loadBalancerStats保存的实例统计信息来选择满足要求的实例
//遍历负载均衡器中维护的所有服务实例
for (Server server: serverList) {
ServerStats serverStats = loadBalancerStats.getSingleServerStat(server);
//过滤掉负载的实例
if (!serverStats.isCircuitBreakerTripped(currentTime)) {
int concurrentConnections = serverStats.getActiveRequestsCount(currentTime);
//找出请求数最小的一个
if (concurrentConnections < minimalConcurrentConnections) {
minimalConcurrentConnections = concurrentConnections;
chosen = server;
}
}
}
if (chosen == null) {
return super.choose(key);
} else {
return chosen;
}
}
@Override
public void setLoadBalancer(ILoadBalancer lb) {
super.setLoadBalancer(lb);
if (lb instanceof AbstractLoadBalancer) {
loadBalancerStats = ((AbstractLoadBalancer) lb).getLoadBalancerStats();
}
}
}