yudaocode/SpringBoot-Labs · error · IllegalStateException

获取不到实例

Error message

获取不到实例

What it means

Same guard as the demo01 consumer, in the labx-22 demo02 variant (Eureka): DemoConsumerApplication fetches DiscoveryClient.getInstances("demo-provider"), takes instances.get(0) only when the list is non-empty, and otherwise throws IllegalStateException("获取不到实例") at line 59. The registry query returned zero instances for the service name 'demo-provider'. In the demo02 lab the provider module is the demo02 provider — the consumer code still hard-codes the logical name 'demo-provider', so a name/config mismatch between the demo02 provider's spring.application.name and this literal is a frequent cause unique to this variant.

Source

Thrown at labx-22/labx-22-scn-eureka-demo02-consumer/src/main/java/cn/iocoder/springcloudalibaba/labx22/consumerdemo/DemoConsumerApplication.java:59

        private RestTemplate restTemplate;
        @Autowired
        private LoadBalancerClient loadBalancerClient;

        @GetMapping("/hello")
        public String hello(String name) {
            // 获得服务 `demo-provider` 的一个实例
            ServiceInstance instance;
            if (true) {
                // 获取服务 `demo-provider` 对应的实例列表
                List<ServiceInstance> instances = discoveryClient.getInstances("demo-provider");
                // 选择第一个
                instance = instances.size() > 0 ? instances.get(0) : null;
            } else {
                instance = loadBalancerClient.choose("demo-provider");
            }
            // 发起调用
            if (instance == null) {
                throw new IllegalStateException("获取不到实例");
            }
            String targetUrl = instance.getUri() + "/echo?name=" + name;
            String response = restTemplate.getForObject(targetUrl, String.class);
            // 返回结果
            return "consumer:" + response;
        }

    }

}

View on GitHub (pinned to 6c12efaed0)

Solutions

1. Open the Eureka dashboard and confirm a service named exactly 'demo-provider' (the name passed to getInstances) is UP; fix the provider's spring.application.name if it differs.
2. Reorder startup: Eureka server → demo02 provider → wait for UP status → consumer; then retry the request.
3. Align eureka.client.serviceUrl.defaultZone between provider and consumer so both talk to the same registry.
4. Handle the empty case gracefully (503 + message) or use LoadBalancerClient.choose with a null check when absence is expected.

Example fix

// before
instance = instances.size() > 0 ? instances.get(0) : null;
if (instance == null) {
    throw new IllegalStateException("获取不到实例");
}

// after
if (instances.isEmpty()) {
    return "service demo-provider unavailable, please retry later";
}
ServiceInstance instance = instances.get(0);

List<ServiceInstance> instances = discoveryClient.getInstances("demo-provider");
if (instances.isEmpty()) {
    return "demo-provider 暂无可用实例，请确认提供者已注册并稍后重试";
}
ServiceInstance instance = instances.get(0);

Optional<ServiceInstance> firstInstance(DiscoveryClient dc, String service) {
    List<ServiceInstance> list = dc.getInstances(service);
    return (list == null || list.isEmpty()) ? Optional.empty() : Optional.of(list.get(0));
}

try {
    return "consumer:" + restTemplate.getForObject(targetUrl, String.class);
} catch (RestClientException e) {
    // instance disappeared between discovery and call: refresh and retry once
    List<ServiceInstance> retry = discoveryClient.getInstances("demo-provider");
    if (retry.isEmpty()) throw new IllegalStateException("获取不到实例");
    return "consumer:" + restTemplate.getForObject(retry.get(0).getUri() + "/echo?name=" + name, String.class);
}

When it happens

Trigger: Calling the consumer endpoint while getInstances("demo-provider") is empty: provider (demo02) not started, registered under a different spring.application.name, registration still propagating, Eureka server unreachable from either side, or the instance evicted (lease expiry / health-check failure).

Common situations: Provider started but with a name other than 'demo-provider'; consumer pointed at a different Eureka server than the provider (mismatched eureka.client.serviceUrl.defaultZone); consumer started immediately after the provider so the local fetch cache has not refreshed yet; provider crashed after registration and Eureka evicted it; copy-pasting this consumer against a provider from another lab module.

Related errors

• 获取不到实例
• 获取不到实例
• 获取不到实例
• 获取不到实例
• 获取不到实例

AI-assisted analysis of yudaocode/SpringBoot-Labs@6c12efaed0 (2026-08-14). Data as JSON: /api/errors/8ef9155dc9a92097. Report an issue: GitHub.