如何根据jobParameters通过Spring-Expression-Language或其他方式有条件地注入bean？

Question

我正在尝试创建一个包含多个FlatFileItemWriters的CustomWriter。配置是通过xml实现的。我希望根据jobParameters中的值将FlatFileItemWriters注入到CustomWriter中；如下所示-

<bean id="customWriter" class="com.company.writer.CustomDataWriter" scope="step">
    <property name="chapatiDataWriter" ref="#{jobParameters['chapatiSection'] != null ? chapatiDataWriter : null}"/>
    <property name="anotherDataWriter" ref="anotherDataWriter"/>
    <property name="batchJobConfiguration" value="#{jobParameters['product_configuration']}"/>
</bean>

当我尝试运行应用程序时，我得到；

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'scopedTarget.customWriter' defined in URL [file:./conf/context.xml]: Cannot resolve reference to bean '#{jobParameters['chapatiSection'] != null ? chapatiDataWriter : null}' while setting bean property 'chapatiDataWriter'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'org.springframework.batch.item.file.FlatFileItemWriter@19cb8309' available

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'org.springframework.batch.item.file.FlatFileItemWriter@19cb8309' available
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:805)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1279)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:297)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:330)
    ... 52 common frames omitted

如何根据jobParameters有条件地注入chapatiDataWriter？

Answer 1

即使SpEL非常强大，我也不建议在字符串中使用复杂的代码。我将使用FactoryBean创建自定义编写器，并在XML配置中使用工厂bean：

<bean id="customWriter" class="com.company.writer.CustomDataWriterFactoryBean" scope="step"/>