当Spring依据“类型匹配(type-matching)”规则找到注入点(Injection Point)(例如：randomer)的多个候选Bean时，Spring会查找与注入点的变量名相同的Bean的Name属性，如果找到一个则进行注入，否则抛出异常。See Alsohttps://docs.spring.io/spring/docs/5.1.4.RELEASE/spring-framework-reference/core.html#beans-autowired-annotation-qualifiers

IndexRandomer.java

@Component("indexRandomer")
public class IndexRandomer implements Randomer {
    @Override
    public List<Integer> nextIntList(int bound, int length) {
        List<Integer> list = IntStream.range(0, bound).collect(ArrayList::new, ArrayList::add, ArrayList::addAll);
        Random rnd = new Random();
        List<Integer> result = new ArrayList<>(length);
        for (int i = 0; i < length; i++, bound--) {
            int idx = rnd.nextInt(bound);
            result.add(list.get(idx));
            list.remove(idx);
        }
        return result;
    }
}

LoginController.java

@Component
public class LoginController {
     private Randomer randomer;
 
     /*此处的注入点为构造器的shuffleRandomer变量，虽然依据type-matching规则查询到两个具体Bean：shuffleRandomer和indexRandomer，但是随后Spring
     依据变量名与两个候选Bean的Name匹配得出匹配结果为shuffleRandomer。如果将该shuffleRandomer变量名改写为randomer,则会抛出运行时异常。
     对于一个注入点存在多个候选Bean的情况，可以使用@Primary注解，@Qualifier注解以及变量名与Bean Name匹配的机制进行精确注入*/
    @Autowired
    public LoginController(Randomer shuffleRandomer) {
        this.randomer = shuffleRandomer;
    }
}

ShuffleRandomer.java

@Component("shuffleRandomer")
public class ShuffleRandomer implements Randomer {
    @Override
    public List<Integer> nextIntList(int bound, int length) {
        List<Integer> list = IntStream.range(0, bound).collect(ArrayList::new, ArrayList::add, ArrayList::addAll);
        Collections.shuffle(list);
        return list.subList(0, length);
    }
}