java - 如何根据条件应用Spring消息转换器？

Question

我有一个 Controller ，其响应是驼峰式 json 值。现在我们正在用新版本重写代码，所需的响应位于snake_case中。

我添加了消息转换器并修改了对象映射器来设置setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);

public class ResponseJSONConverter extends MappingJackson2HttpMessageConverter {

@Autowired
public ResponseJSONConverter(ObjectMapper objectMapper) {
    setObjectMapper(objectMapper);
  }
}

我已经向 spring 注册了这个转换器，并且它按预期工作。现在，我希望我的旧端点以驼峰命名法返回，以便向后兼容我的消费者，并以蛇形命名法返回新端点。

我尝试再使用一个带有简单对象映射器的消息转换器，而无需将camelCase设置为Snake case属性并在spring中注册。根据 spring 配置中声明的顺序，仅应用一个消息转换器。

有什么办法可以实现这个目标吗？根据条件加载消息转换器？

编辑

添加了我的 spring 配置文件

 <beans xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">

<bean id="moneySerializer" class="api.serialize.MoneySerializer"/>
    <bean id="moneyDeserializer" class="api.serialize.MoneyDeserializer"/>
    <bean id="serializationModule" class="api.serialize.SerializationModule">
        <constructor-arg index="0" ref="moneySerializer"/>
        <constructor-arg index="1" ref="moneyDeserializer"/>
    </bean>

    <bean id="customObjectMapper" class="api.serialize.CustomObjectMapper" primary="true">
        <constructor-arg ref="serializationModule"/>
    </bean>
    <mvc:annotation-driven>
        <mvc:message-converters register-defaults="true">
            <bean class="api.serialize.ResponseJSONConverterCamelCaseToSnakeCase" >
                <constructor-arg ref="customObjectMapper"/>
            </bean>
            <bean class="api.serialize.ResponseJSONConverter">
                <constructor-arg ref="objectMapper"/>
            </bean>
        </mvc:message-converters>

    </mvc:annotation-driven>

    <bean id="objectMapper" class="com.fasterxml.jackson.databind.ObjectMapper"/>

</beans>

编辑2.0

我的 servlet.xml

<mvc:annotation-driven>
    <mvc:message-converters register-defaults="true">
        <bean class="com.tgt.promotions.api.serialize.ServiceJSONConverter"/>
    </mvc:message-converters>
</mvc:annotation-driven>

自定义消息转换器

    public class ServiceJSONConverter extends MappingJackson2HttpMessageConverter {

    @Autowired
    public ServiceJSONConverter(SnakeCaseObjectMapper snakeCaseObjectMapper) {
        setObjectMapper(snakeCaseObjectMapper);
    }
}

自定义对象映射器

@Component
public class SnakeCaseObjectMapper extends ObjectMapper {
    @Autowired
    public SnakeCaseObjectMapper(PropertyNamingStrategy propertyNamingStrategy) {
        setSerializationInclusion(JsonInclude.Include.NON_NULL);
        setPropertyNamingStrategy(propertyNamingStrategy);
    }
}

自定义属性命名策略

@Component
public class CustomPropertyNamingStrategy extends PropertyNamingStrategy {

    @Autowired
    private HttpServletRequest request;

    private final PropertyNamingStrategy legacyStrategy  = PropertyNamingStrategy.LOWER_CASE;
    private final PropertyNamingStrategy defaultStrategy  = PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES;


    @Override
    public String nameForConstructorParameter(MapperConfig<?> config, AnnotatedParameter ctorParam, String defaultName) {
        return getStrategy().nameForConstructorParameter(config, ctorParam, defaultName);
    }

    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field, String defaultName) {
        return getStrategy().nameForField(config, field, defaultName);
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return getStrategy().nameForGetterMethod(config, method, defaultName);
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config, AnnotatedMethod method, String defaultName) {
        return getStrategy().nameForSetterMethod(config, method, defaultName);
    }

    private PropertyNamingStrategy getStrategy() {
        if (isLegacyEndpoint(request)) {
            return legacyStrategy;
        } else {
            return defaultStrategy;
        }
    }

    private boolean isLegacyEndpoint(HttpServletRequest request) {
        return request != null && request.getRequestURL() != null && !request.getRequestURL().toString().contains("/v3");
    }
}

Answer 1

我建议创建一个 PropertyNamingStrategy 的自定义实现，而不是使用 2 个不同的对象映射器，并相应地使用另外 2 个策略:

public class AwesomePropertyNamingStrategy extends PropertyNamingStrategy {

  private PropertyNamingStrategy legacyStrategy  = PropertyNamingStrategy.LOWER_CASE;
  private PropertyNamingStrategy defaultStrategy  = PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES;

  @Override
  public String nameForConstructorParameter(MapperConfig<?> config, AnnotatedParameter ctorParam, String defaultName) {
    return getStrategy().nameForConstructorParameter(config, ctorParam, defaultName);
  }

  // TODO: implement other nameForXXX methods

  private PropertyNamingStrategy getStrategy() {
    if (isLegacyEndpoint()) {
      return legacyStrategy;
    } else {
      return defaultStrategy;
    }
  }

  private boolean isLegacyEndpoint() {
    // TODO: get hold of the RequestContext or some other thead-local context 
    // that allows you to know it's an old or a new endpoint
    return false;
  }
}

您应该想出一种在旧模式和新模式之间切换的方法:

1. 通过以某种方式访问​​请求上下文来使用端点 URL
2. 如果您的旧端点使用不同的响应对象，请使用正在转换的对象的类来确定旧类/普通类或您自己的所有旧类上的自定义 @LegacyResponse 注释。<