What configuration is required in Spring to use SpEL expressions? SpEL expressions are correctly configured but cannot be used

  java, question

The configuration in XML is as follows:

<bean id="singer" class="com.zdz.bean.Singer" init-method="warmUp" destroy-method="thank">
 <property name="song" ref="song"></property>
 </bean>
 
 <bean id="mocker" class="com.zdz.bean.Mocker">
 <property name="song" ref="#{singer.song.toUpcase()}">
 </property>
 </bean>

The error message is as follows:

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)

I have solved the problem myself, one is because there is no toUpcase method in song, the other is because I want to change the attribute of SpEL expression from ref to value.