如何通过 Autowired 注入具有不同配置的不同 ObjectMapper？

Question

我正在尝试使用 2 个不同的 Jackson ObjectMappers，以便我可以在代码中使用其中任何一个进行切换。 2 个ObjectMappers 的配置会有一些细微差别。

在我的配置文件中，我将它们作为 2 种不同的方式：

@Configuration
public class ApplicationConfiguration {
    private ObjectMapper createMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
        // And a few more other common configurations
        return mapper;
    }

    @Bean
    @Qualifier("standardObjectMapper")
    public ObjectMapper standardObjectMapper() {
        ObjectMapper mapper = createMapper();
        SimpleModule module = new SimpleModule();
        module.addSerializer(Product.class, new StandardProductSerializer());
        mapper.registerModule(module);
        return mapper;
    }

    @Bean
    @Qualifier("specialObjectMapper")
    public ObjectMapper specialObjectMapper() {
        ObjectMapper mapper = createMapper();
        SimpleModule module = new SimpleModule();
        // In this mapper, I have a different serializer for the Product class
        module.addSerializer(Product.class, new SpecialProductSerializer());
        mapper.registerModule(module);
        return mapper;
    }
}

我的计划是在需要时注入并使用其中一个映射器。所以在我的测试中，我有这样的东西：

class SerializationTest {
    @Autowired
    @Qualifier("standardObjectMapper")
    private ObjectMapper standardObjectMapper;

    @Autowired
    @Qualifier("specialObjectMapper")
    private ObjectMapper specialObjectMapper;

    @Test
    void testSerialization() throws JsonProcessingException {
       Product myProduct = new Product("Test Product");

      String stdJson = objectMapper.writeValueAsString(myProduct);
      String specialJson = specialObjectMapper.writeValueAsString(myProduct);

      // Both stdJson and specialJson are of the same value even though they should be different because the mappers have different serializers!
    }
}

但是，2 个ObjectMappers、standardObjectMapper 和specialObjectMapper 似乎都使用相同的StandardProductSerializer。

我希望 specialObjectMapper 使用 SpecialProductSerializer，但事实并非如此。

这 2 个 ObjectMapper 不应该不同吗？我假设注入将基于他们各自的名字，因为他们的类型是相同的？

我应该如何解决这个问题，以便 2 个 ObjectMapper 可以使用不同的序列化器？

---

更新：

我尝试过使用 Qualifiers，但我收到一个错误，即找不到 bean：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'com.site.SerializationTest': Unsatisfied dependency expressed through field 'standardObjectMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.fasterxml.jackson.databind.ObjectMapper' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true), @org.springframework.beans.factory.annotation.Qualifier(value="standardObjectMapper")}

Answer 1

添加@Qualifier 应该可以解决您的问题

@Bean
@Qualifier("standardMapper")
public ObjectMapper standardObjectMapper() {
    ObjectMapper mapper = createMapper();
    SimpleModule module = new SimpleModule();
    module.addSerializer(Product.class, new StandardProductSerializer());
    mapper.registerModule(module);
    return mapper;
}

@Bean
@Qualifier("specialMapper")
public ObjectMapper specialObjectMapper() {
    ObjectMapper mapper = createMapper();
    SimpleModule module = new SimpleModule();
    // In this mapper, I have a different serializer for the Product class
    module.addSerializer(Product.class, new SpecialProductSerializer());
    mapper.registerModule(module);
    return mapper;
}

然后添加@Qualifier 和您的@Autowired

@Autowired
@Qualifier("standardMapper")
private ObjectMapper standardObjectMapper;

@Autowired
@Qualifier("specialMapper")
private ObjectMapper specialObjectMapper;

Answer 2

你可以使用@Qualifier注解来区分不同的ObjectMapper。 （见：https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-autowired-annotation-qualifiers）

@Qualifier("objectMapper1") 
@Autowired
private ObjectMapper objMapper1;

Answer 3

你能试试这个吗，它会根据名字注入bean

@Autowired
@Qualifier("standardObjectMapper")
private ObjectMapper standardObjectMapper;

@Autowired
@Qualifier("specialObjectMapper")
private ObjectMapper specialObjectMapper;

希望这对你有用

Answer 4

可以使用@Qualifier注解：

@Qualifier("specialObjectMapper") 
@Autowired
private ObjectMapper specialObjectMapper;

@Qualifier("standardMapper")
@Autowired
private ObjectMapper standardObjectMapper;

Answer 5

问题是@Configuration-class 在 DI 启动期间没有被扫描。通常，spring会从Application类（注解@SpringBootApplication）所在的包中寻找配置。

我建议将@Configuration 类移到@SpringBootApplication 所在的子包中。

还有其他方法（例如this one described at baelung）来更改组件扫描的根包。但是，除非已用尽所有其他选项，否则我不建议这样做。