Spring Boot 2.5.4 如何实现按名称而非类型自动注入同类型多Bean

问题复现 #

原始配置 #

自定义ObjectMapper Bean配置类：

@Configuration
public class MapperConfig {

    @Bean("yamlMapper")
    public ObjectMapper yamlMapper() {
        return new ObjectMapper(new YAMLFactory());
    }

    @Bean("jsonMapper")
    public ObjectMapper jsonMapper() {
        return new ObjectMapper();
    }

}

服务类注入代码：

@Service
@RequiredArgsConstructor
public class MapperService {

    @Qualifier("jsonMapper")
    private final ObjectMapper jsonMapper;

    @Qualifier("yamlMapper")
    private final ObjectMapper yamlMapper;

}

报错信息 #

启动后抛出如下异常：

No qualifying bean of type 'com.fasterxml.jackson.databind.ObjectMapper' available: expected single matching bean but found 2: yamlMapper,jsonMapper

根因分析 #

报错并非来自自定义的MapperService注入逻辑，而是Spring Boot自带的MappingJackson2HttpMessageConverterConfiguration类默认需要匹配唯一的ObjectMapper类型Bean，该类为框架内置类无法修改其注解配置，因此需要在自定义Bean中指定默认的主Bean供框架底层注入使用。

解决方案 #

通过@Primary注解指定jsonMapper作为默认的ObjectMapper主Bean即可解决冲突，调整后可正常加载上下文的配置如下：

调整后的配置类 #

@Configuration
public class MapperConfig {

    @Bean
    public ObjectMapper yamlMapper() {
        return new ObjectMapper(new YAMLFactory());
    }

    @Bean
    @Primary
    public ObjectMapper jsonMapper() {
        return new ObjectMapper();
    }

}

调整后的服务类 #

@Service
@RequiredArgsConstructor
public class MapperService {

    @Autowired
    @Qualifier("jsonMapper")
    private final ObjectMapper jsonMapper;

    @Autowired
    @Qualifier("yamlMapper")
    private final ObjectMapper yamlMapper;

}

内容的提问来源于stack exchange，提问作者Liam