如何在spring boot 2中使用Sleuth Span

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-sleuth</artifactId>
</dependency>

spring:
  sleuth:
    sampler:
      probability: 1.0

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.sleuth.Span;
import org.springframework.cloud.sleuth.Tracer;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    private static final Logger logger = LoggerFactory.getLogger(MyController.class);

    @Autowired
    private Tracer tracer;

    @GetMapping("/hello")
    public String hello() {
        Span span = tracer.nextSpan().name("helloSpan").start();
        try {
            // 执行一些操作
            logger.info("Hello, Sleuth Span!");
            return "Hello, Sleuth Span!";
        } finally {
            span.end();
        }
    }
}