如何在 springboot 的 ConversionService 中自动装配

Question

尝试在 spring boot 中访问模型中的 Conversion Control，失败。

@Component
public class CityHelperService  {

    @Autowired
    ConversionService conversionService;// = ConversionServiceFactory.registerConverters();

    public City toEntity(CityDTO dto){
        City entity = conversionService.convert(dto, City.class);
        return entity;
    }

    public CityDTO toDTO(City entity){
        CityDTO dto = conversionService.convert(entity, CityDTO.class);
        return dto;
    }
}

显示以下错误：

Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.lumiin.mytalk.model.CityModel com.lumiin.mytalk.controllers.CityController.cityModel;
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'cityModel' defined in file : Unsatisfied dependency expressed through constructor argument with index 1 of type [com.lumiin.mytalk.dao.CityHelperService]: : Error creating bean with name 'cityHelperService': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.springframework.core.convert.ConversionService com.lumiin.mytalk.dao.CityHelperService.conversionService;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)};
nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cityHelperService': Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: org.springframework.core.convert.ConversionService com.lumiin.mytalk.dao.CityHelperService.conversionService;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Answer 1

显然没有 ConversionService bean 可用，根据最后一个嵌套异常判断：

org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.core.convert.ConversionService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency.

查看 Spring documentation 揭示，您应该声明一个 ConversionService bean。在 XML 配置中，它看起来像这样：

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="example.MyCustomConverter"/>
        </set>
    </property>
</bean>

并且由于您使用的是 Spring Boot，我假设您正在以编程方式创建上下文，因此您应该创建一个用 @Bean 注释的方法，其中 returns a ConverstionService，像这样 (explained here):

@Bean(name="conversionService")
public ConversionService getConversionService() {
    ConversionServiceFactoryBean bean = new ConversionServiceFactoryBean();
    bean.setConverters(...); //add converters
    bean.afterPropertiesSet();
    return bean.getObject();
}

Answer 2

不完全同意已接受的答案，因为会有一个名为 mvcConversionService 的默认 ConverstionService，因此您会得到 重复 bean 异常。相反 addConverter 到 FormatterRegistry，这里是部分答案的 link：

Java Config equivalent for conversionService / FormattingConversionServiceFactoryBean

此外，您还需要（在某些情况下）为 ConversionService 至少定义一个空的 Component，如下所示：

@Component @Primary
public class MyConversionService extends DefaultConversionService implements ConversionService {
    // an empty ConversionService to initiate call to register converters
}

这是为了强制 spring 容器发起调用：

class WebMvcConfigurerAdapter {
    ...

    public void addFormatters(FormatterRegistry registry) {
         //registry.addConverter(...);
    }
}

如何在 springboot 的 ConversionService 中自动装配

How to Autowired in ConversionService in springboot

java

spring

spring-mvc

spring-boot