java - Spring中需要什么配置才能使用SpEL表达式？正确配置了SpEL表达式却无法使用

XML中配置如下：

出错信息如下：

       org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mocker' defined in class path resource [beans.xml]: Cannot resolve reference to bean '#{singer.song.toUpcase()}' while setting bean property 'song'; nested exception is org.springframework.beans.factory.BeanExpressionException: Expression parsing failed; nested exception is org.springframework.expression.spel.SpelEvaluationException: EL1004E:(pos 12): Method call: Method toUpcase() cannot be found on com.zdz.util.Song type
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:359)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:108)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1477)