[享学Netflix] 五十三、Ribbon的LoadBalancer五大组件之：IRule（三）随机和重试，所有IRule实现总结

public class RandomRule extends AbstractLoadBalancerRule {

	public Server choose(ILoadBalancer lb, Object key) {
		...
		Server server = null;
		while (server == null) {
			...
			List<Server> upList = lb.getReachableServers();
			List<Server> allList = lb.getAllServers();
			int serverCount = allList.size();
            int index = chooseRandomInt(serverCount);
            server = upList.get(index);
            ...
		}
		return server;
	}

    protected int chooseRandomInt(int serverCount) {
        return ThreadLocalRandom.current().nextInt(serverCount);
    }

	@Override
	public Server choose(Object key) {
		return choose(getLoadBalancer(), key);
	}
}

@Test
public void fun2() throws InterruptedException {
    List<Server> serverList = new ArrayList<>();
    serverList.add(createServer("华南", 1));
    serverList.add(createServer("华东", 1));
    serverList.add(createServer("华东", 2));

    serverList.add(createServer("华北", 1));
    serverList.add(createServer("华北", 2));
    serverList.add(createServer("华北", 3));
    serverList.add(createServer("华北", 4));

    // 轮询策略：因为Servers均来自于lb，所以必须关联上一个lb实例哦
    ILoadBalancer lb = new BaseLoadBalancer();
    lb.addServers(serverList);
    RandomRule rule = new RandomRule();
    rule.setLoadBalancer(lb);
    System.out.println("server总数："+lb.getAllServers().size());
    System.out.println("up的总数："+lb.getReachableServers().size());

    while (true) {
        System.out.println(rule.choose(null));
        TimeUnit.SECONDS.sleep(2);
    }
}


private Server createServer(String zone, int index) {
    Server server = new Server("www.baidu" + zone + ".com", index);
    server.setAlive(true);
    server.setReadyToServe(true);
    server.setZone(zone);
    return server;
}

server总数：7
up的总数：7
www.baidu华东.com:1
www.baidu华北.com:1
www.baidu华北.com:1
www.baidu华北.com:2
www.baidu华北.com:1
www.baidu华东.com:1
www.baidu华南.com:1
...

lb.setPing(server -> server.getPort() % 10 > 2);

server总数：7
up的总数：2
java.lang.IndexOutOfBoundsException: Index: 1, Size: 0

	at java.util.ArrayList.rangeCheck(ArrayList.java:657)
	at java.util.ArrayList.get(ArrayList.java:433)
	at java.util.Collections$UnmodifiableList.get(Collections.java:1309)
	at com.netflix.loadbalancer.RandomRule.choose(RandomRule.java:61)
	at com.netflix.loadbalancer.RandomRule.choose(RandomRule.java:92)

public class RetryRule extends AbstractLoadBalancerRule {

	IRule subRule = new RoundRobinRule();
	// 最大重试时长  默认值是半分钟
	long maxRetryMillis = 500;
	
	... // 省略给这两个属性赋值的构造器和set方法们
	@Override
	public void setLoadBalancer(ILoadBalancer lb) {		
		super.setLoadBalancer(lb);
		subRule.setLoadBalancer(lb);
	}
	
	@Override
	public Server choose(Object key) {
		return choose(getLoadBalancer(), key);
	}

	// 选择方法
	public Server choose(ILoadBalancer lb, Object key) {
		// 计算出一个开始选择  和  结束选择的时间
		long requestTime = System.currentTimeMillis();
		long deadline = requestTime + maxRetryMillis;

		// 先通过subRule选择出一个server
		Server answer = null;
		answer = subRule.choose(key);
		
		// 如果选择出的Server为null，或者不是活的
		// 并且还在结束时间之前，就执行重试策略
		if (((answer == null) || (!answer.isAlive())) 
			&& (System.currentTimeMillis() < deadline)) {

			InterruptTask task = new InterruptTask(deadline - System.currentTimeMillis());

			while (!Thread.interrupted()) {
				... // 持续不断的调用subRule.choose(key)，知道获取到或者时间到了
			}
			task.cancel();
		}
		
		// 如果最终还是没获取到可用的，那就返回null。否则返回正常结果
		if ((answer == null) || (!answer.isAlive())) {
			return null;
		} else {
			return answer;
		}
	}
}