[享学Netflix] 五十五、Ribbon负载均衡器执行上下文：LoadBalancerContext

public class LoadBalancerContext implements IClientConfigAware {

	protected String clientName = "default";
	protected String vipAddresses;
	protected int maxAutoRetriesNextServer = DefaultClientConfigImpl.DEFAULT_MAX_AUTO_RETRIES_NEXT_SERVER;
	protected int maxAutoRetries = DefaultClientConfigImpl.DEFAULT_MAX_AUTO_RETRIES;
	protected RetryHandler defaultRetryHandler = new DefaultLoadBalancerRetryHandler();
	protected boolean okToRetryOnAllOperations = DefaultClientConfigImpl.DEFAULT_OK_TO_RETRY_ON_ALL_OPERATIONS.booleanValue();

	private ILoadBalancer lb;
	private volatile Timer tracer;
}

LoadBalancerContext：

	// 记录一个状态，需要传入rt，所以肯定代表请求已经结束了喽。让是个私有方法，旨在本类被调用
	// 1、activeRequestsCount -1
	// 2、totalRequests +1（注意：总请求数是在完成时候+1的，而非请求的时候哦）
	// 3、记录rt（包括时间窗口收集dataDist以及历史统计的responseTimeDist）
    private void recordStats(ServerStats stats, long responseTime) {
    	if (stats == null) {
    		return;
    	}
        stats.decrementActiveRequestsCount();
        stats.incrementNumRequests();
        stats.noteResponseTime(responseTime);
    }

	// ========重要========此方法表示请求完成后调用
	// 请求完成：在接收到响应或从客户端抛出异常（出错）
	// response：返回值
	public void noteRequestCompletion(ServerStats stats, Object response, Throwable e, long responseTime, RetryHandler errorHandler) {
    	if (stats == null) {
    		return;
    	}
		recordStats(stats, responseTime);
		// 很明显：callErrorHandler永远不可能为null（排除故意把重拾起set为null的情况）
		RetryHandler callErrorHandler = errorHandler == null ? getRetryHandler() : errorHandler;
		
		// 判断看看是否出错了，是否需要重试
		// 有response那就是正常返回：该请求正常，那就把重复连续失败的count清零
		if (callErrorHandler != null && response != null) {
			stats.clearSuccessiveConnectionFailureCount();
		} else if (callErrorHandler != null && e != null) {
			// 如果是熔断类型的异常，那就连续次数 + 1
			// 失败总数也+1(窗口统计)
			if (callErrorHandler.isCircuitTrippingException(e)) {
				stats.incrementSuccessiveConnectionFailureCount(); 
				stats.addToFailureCount();
			
			// 表示虽然失败了，但是是其它异常，比如你的业务异常，比如NPE
			// 那就清零。再次证明：ribbon的熔断只管它自己是被的异常（链接异常）
			// 并不管业务异常，业务异常交给hystrix才是合理的
			} else {
				stats.clearSuccessiveConnectionFailureCount();
			}
		}
	}

	// 客户端执行请求之前调用。增加一个活跃连接数
	public void noteOpenConnection(ServerStats serverStats) {
		serverStats.incrementActiveRequestsCount();
	}

LoadBalancerContext：

	// 仅仅根据URI就拿到端口
	// http 80  /  https 443
	protected Pair<String, Integer> deriveSchemeAndPortFromPartialUri(URI uri) { ... }

	// 从虚拟地址中尝试获取到主机的host和port
	// 如果虚拟地址确实包含实际的主机，那就直接拿。如虚拟地址就是：localhost:8080
	protected  Pair<String, Integer> deriveHostAndPortFromVipAddress(String vipAddress) throws URISyntaxException, ClientException {
		...
        if (host == null) {
            throw new ClientException("Unable to derive host/port from vip address " + vipAddress);
        }
        int port = uri.getPort();
        if (port < 0) {
            port = getDefaultPortFromScheme(scheme);
        }
        if (port < 0) {
            throw new ClientException("Unable to derive host/port from vip address " + vipAddress);
        }
        hostAndPort.setFirst(host);
        hostAndPort.setSecond(port);
        return hostAndPort;
	}

	// 检测你配置的vipAddress是否是被认证过的
	//若配置了多个，只要有一个符合要求，就返回true
	private boolean isVipRecognized(String vipEmbeddedInUri) {
		// vipAddresses是上下文中指定的，也就是你配置的，可以使用逗号分隔配置多个
        if (vipAddresses == null) {
            return false;
        }
        
		// 配置了多个的话，就一个一个的检查
		// 只要有一个地址值是被认证过的，那就返回true
		String[] addresses = vipAddresses.split(",");
        for (String address: addresses) {
            if (vipEmbeddedInUri.equalsIgnoreCase(address.trim())) {
                return true;
            }
        }
        return false;
	}

<scheme>://<user>:<password>@<host>:<port>/<path>;<params>?<query>#<fragment>

public static void main(String[] args) {
    URI original = URI.create("www.baidu.com:8080");
    System.out.println(original.getScheme()); // www.baidu.com（诧异不？）
    System.out.println(original.getHost()); // null
    System.out.println(original.getPort()); // -1
    System.out.println(original.getAuthority()); // null

    original = URI.create("tcp://www.baidu.com:8080");
    System.out.println(original.getScheme()); // tcp
    System.out.println(original.getHost()); // www.baidu.com
    System.out.println(original.getPort()); // 8080
    System.out.println(original.getAuthority()); // www.baidu.com:8080
}

LoadBalancerContext：

	//original这个URI可能是无host无ip的，如/api/v1/ping。所以此处需要处理
	// 注意：调用此方法两个入参均可能为null哦
	public Server getServerFromLoadBalancer(@Nullable URI original, @Nullable Object loadBalancerKey) throws ClientException {
		
		if (host == null) {
			if (lb != null) {
				Server svc = lb.chooseServer(loadBalancerKey);
			} else {
				Pair<String,Integer> hostAndPort = deriveHostAndPortFromVipAddress(vipAddresses);
				host = hostAndPort.first();
				port = hostAndPort.second();
			}
		} else {
			shouldInterpretAsVip = isVipRecognized(original.getAuthority());
			if (shouldInterpretAsVip) {
				Server svc = lb.chooseServer(loadBalancerKey);
			} else {
				logger.debug("Using full URL passed in by caller (not using load balancer): {}", original);
			}
		}

        if (host == null){
            throw new ClientException(ClientException.ErrorType.GENERAL,"Request contains no HOST to talk to");
        }
        return new Server(host, port);
	}

@Test
public void fun1() throws ClientException {
    URI original = URI.create("");

    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));

    BaseLoadBalancer lb = new BaseLoadBalancer();
    lb.addServers(serverList);
    IClientConfig config = DefaultClientConfigImpl.getClientConfigWithDefaultValues("YourBatman");
    LoadBalancerContext loadBalancerContext = new LoadBalancerContext(null, config);

    for (int i = 0; i < 5; i++) {
        System.out.println(loadBalancerContext.getServerFromLoadBalancer(original, null));
    }
}

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

www.baidu华东.com:1
www.baidu华东.com:2
www.baidu华北.com:1
www.baidu华北.com:2
www.baidu华北.com:3

www.baiud.com:9999
www.baiud.com:9999
www.baiud.com:9999
www.baiud.com:9999
www.baiud.com:9999

account:3333
account:3333
account:3333
account:3333
account:3333

www.baidu华东.com:1
www.baidu华东.com:2
www.baidu华北.com:1
www.baidu华北.com:2
www.baidu华北.com:3

LoadBalancerContext：

	public URI reconstructURIWithServer(Server server, URI original) {
		// 若original里已经有了host、port、scheme等，那还解析个啥 你已经是完整的了
        String host = server.getHost();
        int port = server.getPort();
        String scheme = server.getScheme();        
        if (host.equals(original.getHost()) 
                && port == original.getPort()
                && scheme == original.getScheme()) {
            return original;
        }
        ... //  使用server里的host、port等完成拼接，形成一个完整的URI返回
	}