如何在springboot中的ConversionService中自动装配

Posted 2023-02-26

【中文标题】如何在springboot中的ConversionService中自动装配

【英文标题】：How to Autowired in ConversionService in springboot

【发布时间】：2015-07-14 09:34:25

【问题描述】：

试图在springboot中访问模型中的ConversionControl，没有成功。

@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;
    

它显示以下错误：

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)

【参考方案1】：

显然没有可用的ConversionService bean，从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 显示，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>

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带有 @Bean 注释的方法，该方法返回一个 ConverstionService，如下所示 (explained here)：

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

【讨论】：

感谢您的 cmets..但是什么是 bean.setConverters(...);它显示一个错误 - org.springframework.core.convert.ConverterNotFoundException: 没有找到能够从 com.lumiin.mytalk.dto.CityDTO 类型转换为 com.lumiin.mytalk.model.City 类型的转换器

你可能没有指定一个转换器——你必须创建一个类，它实现接口Converter<City, CityDTO>，另一个相反，然后在ConversionServiceFactoryBean中注册。请看本教程：javabeat.net/introduction-to-spring-converters-and-formatters

在Javaconfig中，你甚至不需要像上面的例子一样从ConversionServiceFactoryBean返回一个ConverstionService，只需要返回一个ConversionServiceFactoryBean bean，spring会为你做剩下的

【参考方案2】：

不完全同意接受的答案，因为会有一个名为 mvcConversionService 的默认 ConverstionService，所以你会得到 duplicate bean exception。而不是addConverter 到FormatterRegistry，这里是部分答案的链接：

Java Config equivalent for conversionService / FormattingConversionServiceFactoryBean

您还需要（在某些情况下）为ConversionService 定义至少一个空的Component，如下所示：

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

这是强制spring容器发起调用：

class WebMvcConfigurerAdapter 
    ...

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

【讨论】：

只有在项目中有 org.springframework.boot:spring-boot-starter-web 依赖项时，mvcConversionService 才会出现