springcloud ribbon 拦截resttemplate到实际请求调用源码讲解

LoadBalancerInterceptor

将一个普通的RestTemplate 变成客户端负载均衡

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

private LoadBalancerClient loadBalancer;

private LoadBalancerRequestFactory requestFactory;

//由于我们在使用RestTemplate时采用了服务名作为host,所以直接从HttpRequest的URI对象中通过getHost,

就可以拿到服务名，然后调用execute函数去根据服务名来选择实例并发起实际的请求

@Override

public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,

final ClientHttpRequestExecution execution) throws IOException {

final URI originalUri = request.getURI();

String serviceName = originalUri.getHost();

Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);

return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));

}

}

RibbonLoadBalancerClient 下的 execute

通过getServer 选取具体的服务器进行调用

request.apply 最后还是委派 spring 下 ClientHttpRequest

其调用过程是

LoadBalancerRequestFactory#apply

-->

InterceptingClientHttpRequest#execute

-->

InterceptingClientHttpRequest# org.springframework.http.client.ClientHttpRequest

@Override

public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {

ILoadBalancer loadBalancer = getLoadBalancer(serviceId);

Server server = getServer(loadBalancer);

RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,

serviceId), serverIntrospector(serviceId).getMetadata(server));

T returnVal = request.apply(ribbonServer);

}

RibbonLoadBalancerClient 下的 getServer(ILoadBalancer loadBalancer

)

protected Server getServer(ILoadBalancer loadBalancer) {

if (loadBalancer == null) {

return null;

}

return loadBalancer.chooseServer("default"); // TODO: better handling of key

}

调用链

默认：

ZoneAwareLoadBalancer#chooseServer

调用父类

---> BaseLoadBalancer#chooseServer

---> ZoneAvoidanceRule#choose

ZoneAvoidanceRule#choose 方法，默认采用的是incrementAndGetModulo 即轮询

public Server choose(Object key) {

ILoadBalancer lb = getLoadBalancer();

Optional<Server> server = getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);

if (server.isPresent()) {

return server.get();

} else {

return null;

}

}

private int incrementAndGetModulo(int modulo) {

for (;;) {

int current = nextIndex.get();

int next = (current + 1) % modulo;

if (nextIndex.compareAndSet(current, next) && current < modulo)

return current;

}

}