将ConversionService注入自定义转换器

Question

使用Spring mvc-3。我正在编写一个自定义转换器，需要访问注册到ConversionService的其他转换器。

我如何才能做到这一点呢？我试着把我的自定义转换器写成：

  class CustomConverter<X, Y>{
     @Autowired ConversionService service;
     //+getter & setters of service

     public Y convert(X input){
          // I need access to service to lookup simple conversions such as
          // String array to Long array etc..

     }

  }

我通过applicationContext.xml注册了我的自定义转换器

  <bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
     <property name = "converters">
         <list>
            <bean class="CustomConverter"/>
         </list>
     </property>
  </bean>

然而，spring拒绝向我的CustomConverter注入服务(它总是为空)。我如何才能做到这一点呢？

谢谢!

Answer 1

我最近使用了类似的东西来解决这个问题。使用自定义工厂：

public class MyConversionServiceFactoryBean extends ConversionServiceFactoryBean {

    @Override
    public void afterPropertiesSet() {
        super.afterPropertiesSet();
        ConversionService conversionService = getObject();
        ConverterRegistry registry = (ConverterRegistry) conversionService;
        // register converters that need a nested conversion service
        registry.addConverter(new MyCustomConverter(conversionService));
    }
}

它是这样声明的：

<bean id="conversionService"
    class="com.company.MyConversionServiceFactoryBean">
    <property name="converters">
        <list>
            ... declare standard converters here ...
        </list>
    </property>
</bean>

Answer 2

我也遇到过同样的问题。Spring JIRA中有一个issue SPR-6415来解决这个问题。基于对这个问题的讨论，我在这里给出了我的解决方案。它的原理与@nmervaillie的answer相同，但您不必实现自己的ConversionServiceFactoryBean。

/**
 * Base class of @{code Converter} that need to use {@code ConversionService}.
 * Instances of implementing classes must be spring-managed to inject ConversionService.
 * 
 * @author Michal Kreuzman
 */
public abstract class CoversionServiceAwareConverter<S, T> implements Converter<S, T> {

  @Inject
  private ConversionService conversionService;

  protected ConversionService conversionService() {
    return conversionService;
  }

  /**
   * Add this converter to {@code ConverterRegistry}.
   */
  @SuppressWarnings("unused")
  @PostConstruct
  private void register() {
    if (conversionService instanceof ConverterRegistry) {
      ((ConverterRegistry) conversionService).addConverter(this);
    } else {
      throw new IllegalStateException("Can't register Converter to ConverterRegistry");
    }
  }
}

@Component
public class SampleConverter extends CoversionServiceAwareConverter<Object, Object> {

    @Override
    public String convert(Object source) {
        ConversionService conversionService = conversionService();

        // Use conversionService and convert
    }
}

Answer 3

我在以spring-ws为中心的应用程序中解决了这个问题。此解决方案的主要组件包括：

• 将转换器实现声明为spring beans在ConversionServiceFactoryBean

中的注入点上使用@Lazy from spring-

• 所有在spring bean中发现的转换器

SampleConverter

@Component
public class SampleConverter implements Converter<Source, Target> {

private ConversionService conversionService;

    @Inject
    @Lazy
    public SampleConverter(ConversionService conversionService){
        this.conversionService = conversionService; 
    }

    @Override
    public Target convert(Source source){
        Target target = new Target();
        ...
    target.setTargetDetails(conversionService.convert(source.getSourceDetails, TargetDetails.class); 
    ...

和配置：

@Configuration
public class ConversionServiceConfig {

    @Bean
    public ConversionService conversionService(Set<Converter<?,?>> converters){
        ConversionServiceFactoryBean csfb = new ConversionServiceFactoryBean();
        csfb.setConverters(converters); 
        csfb.afterPropertiesSet(); 
        return csfb.getObject(); 
   }

..。

@Lazy注释通过注入代理来绕过鸡蛋鸡问题，从而延迟转换服务bean的解析，直到它真正被使用。