当SpringCloud微服务发生线程隔离（舱壁模式）和熔断降级时（微服务失败的回调），利用FeignClient整合Sentinel，返回用户一个友好提示或者默认结果

在Spring Cloud微服务中实现线程隔离（栅栏模式）和熔断降级时的回调，可以使用Hystrix的HystrixCommand和HystrixObservableCommand。以下是一个简单的例子：

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixObservableCommand;
import rx.Observable;
 
public class MicroserviceCommand extends HystrixCommand<String> {
    private final String serviceName;
 
    public MicroserviceCommand(String serviceName) {
        super(HystrixCommand.Setter
                .withGroupKey(HystrixCommandGroupKey.Factory.asKey("MicroserviceGroup"))
                .andCommandKey(HystrixCommandKey.Factory.asKey("MicroserviceCommand")));
        this.serviceName = serviceName;
    }
 
    @Override
    protected String run() throws Exception {
        // 调用远程微服务
        String response = callRemoteService(serviceName);
        return response;
    }
 
    private String callRemoteService(String serviceName) {
        // 模拟远程调用
        return "Response from " + serviceName;
    }
 
    @Override
    protected Observable<String> resumeWithFallback() {
        return Observable.just("Fallback response");
    }
}

在这个例子中，MicroserviceCommand 继承自 HystrixCommand，用于调用远程微服务。如果远程调用失败，Hystrix会执行回退逻辑resumeWithFallback()，返回一个默认的回退响应。

对于返回Observable的情况，可以使用HystrixObservableCommand：

import com.netflix.hystrix.HystrixObservableCommand;
import rx.Observable;
 
public class ObservableMicroserviceCommand extends HystrixObservableCommand<String> {
    private final String serviceName;
 
    public ObservableMicroserviceCommand(String serviceName) {
        super(HystrixCommand.Setter
                .withGroupKey(HystrixCommandGroupKey.Factory.asKey("MicroserviceGroup"))
                .andCommandKey(HystrixCommandKey.Factory.asKey("ObservableMicroserviceCommand")));
        this.serviceName = serviceName;
    }
 
    @Override
    protected Observable<String> construct() {
        // 调用远程微服务
        return callRemoteServiceObservable(serviceName);
    }
 
    private Observable<String> callRemoteServiceObserva