Spring Boot构造函数中的意外错误

Question

我写了一个样例程序，如下所示。

@Configuration
public class MyclassName{

    private final List<String> tableIds;

    public MyclassName(
        List<String> tableIds) {
        this.tableIds = tableIds;
    }
}

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of constructor in MyclassName required a single bean, but 4 were found:
    - spring.sleuth.baggage-keys: defined by method 'baggageKeys' in class path resource [org/springframework/cloud/sleuth/autoconfig/TraceBaggageConfiguration.class]
    - spring.sleuth.local-keys: defined by method 'localKeys' in class path resource [org/springframework/cloud/sleuth/autoconfig/TraceBaggageConfiguration.class]
    - spring.sleuth.propagation-keys: defined by method 'propagationKeys' in class path resource [org/springframework/cloud/sleuth/autoconfig/TraceBaggageConfiguration.class]
    - spring.sleuth.log.slf4j.whitelisted-mdc-keys: defined by method 'whiteListedMDCKeys' in class path resource [org/springframework/cloud/sleuth/autoconfig/TraceBaggageConfiguration.class]


Action:

Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed


Process finished with exit code 0

Answer 1

类MyClassName是spring框架所知道的。

因此spring将尝试使用构造函数创建MyClassName的实例：

public MyclassName(List<String> tableIds)

MyClassName中构造函数的参数0是list tableids

@Bean(BAGGAGE_KEYS)
@ConfigurationProperties(BAGGAGE_KEYS)
List<String> baggageKeys() {...}

@Bean(LOCAL_KEYS)
@ConfigurationProperties(LOCAL_KEYS)
List<String> localKeys()  {...}

@Bean(PROPAGATION_KEYS)
@ConfigurationProperties(PROPAGATION_KEYS)
List<String> propagationKeys()  {...}

@Bean(WHITELISTED_MDC_KEYS)
@ConfigurationProperties(WHITELISTED_MDC_KEYS)
List<String> whiteListedMDCKeys()  {...}

首先对预期bean进行限定（给出id）

@Bean("myExpectedTableIds")
List<String> myTableIdsProcucerMethod()

然后使用org.springframework.beans.factory.annotation.qualifier注释告诉Spring您真正想要的bean：

public MyclassName(@Qualifier("myExpectedTableIds") List<String> tableIds)