spring @Cacheable使用SpEL异常：org.springframework.expression.spel.SpelParseException: Unexpected token. Expected 'identifier' but was 'lcurly({)'

springboot结合redis做缓存，在@Cacheable中使用如下SpEL时报错。

@Cacheable(cacheNames = ENTERPRISE_CACHE_KEY, key = "#{T(com.emax.common.RestApiSignUtil).foo(#root.args[0])}")

异常：

org.springframework.expression.spel.SpelParseException: Expression [#{T(com.emax.common.RestApiSignUtil).foo(#root.args[0])}] @1: EL1043E: Unexpected token. Expected 'identifier' but was 'lcurly({)'

异常stacktrace信息：

org.springframework.expression.spel.SpelParseException: Expression [#{T(com.emax.common.RestApiSignUtil).foo(#root.args[0])}] @1: EL1043E: Unexpected token. Expected 'identifier' but was 'lcurly({)'

    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.internalException(InternalSpelExpressionParser.java:1044)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatToken(InternalSpelExpressionParser.java:926)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.maybeEatFunctionOrVar(InternalSpelExpressionParser.java:423)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatStartNode(InternalSpelExpressionParser.java:512)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatPrimaryExpression(InternalSpelExpressionParser.java:351)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatUnaryExpression(InternalSpelExpressionParser.java:345)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatPowerIncDecExpression(InternalSpelExpressionParser.java:304)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatProductExpression(InternalSpelExpressionParser.java:282)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatSumExpression(InternalSpelExpressionParser.java:264)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatRelationalExpression(InternalSpelExpressionParser.java:218)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatLogicalAndExpression(InternalSpelExpressionParser.java:205)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatLogicalOrExpression(InternalSpelExpressionParser.java:192)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.eatExpression(InternalSpelExpressionParser.java:153)
    at org.springframework.expression.spel.standard.InternalSpelExpressionParser.doParseExpression(InternalSpelExpressionParser.java:131)
    at org.springframework.expression.spel.standard.SpelExpressionParser.doParseExpression(SpelExpressionParser.java:61)
    at org.springframework.expression.spel.standard.SpelExpressionParser.doParseExpression(SpelExpressionParser.java:33)
    at org.springframework.expression.common.TemplateAwareExpressionParser.parseExpression(TemplateAwareExpressionParser.java:52)
    at org.springframework.expression.common.TemplateAwareExpressionParser.parseExpression(TemplateAwareExpressionParser.java:43)
    at org.springframework.context.expression.CachedExpressionEvaluator.getExpression(CachedExpressionEvaluator.java:88)
    at org.springframework.cache.interceptor.CacheOperationExpressionEvaluator.key(CacheOperationExpressionEvaluator.java:104)
    at org.springframework.cache.interceptor.CacheAspectSupport$CacheOperationContext.generateKey(CacheAspectSupport.java:778)
    at org.springframework.cache.interceptor.CacheAspectSupport.generateKey(CacheAspectSupport.java:575)
    at org.springframework.cache.interceptor.CacheAspectSupport.findCachedItem(CacheAspectSupport.java:518)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:401)
    at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:345)
    at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)
    at com.emax.MyService$$EnhancerBySpringCGLIB$$4de73e25.getEnterpriseByEntId(<generated>)
    at com.emax.MyServiceTest.getEnterpriseByEntId(MyServiceTest.java:21)

identifier、lcurly都是什么？一脸懵逼。
顺着stacktrace点进去看源码，才确定lcurly表示左大括号“{”。看来不能用“{”。下面是正确答案：

@Cacheable(cacheNames = ENTERPRISE_CACHE_KEY, key = "T(com.emax.common.RestApiSignUtil).foo(#root.args[0])")

在SpEL中可以调用类的方法，足见SpEL的强大！

扩展：@Cacheable中SpEL的用法列举

// 下面方式可以同时设置两个缓存； 取参数可以用#param形式
@Cacheable(cacheNames = {ENTERPRISE_CACHE_KEY, "test-another-key"}, key = "#enterpriseId eq 0 ? 0: #enterpriseId")
public Result baseEnterpriseByEntId(Long enterpriseId) {...}

-------------------------------------------------

// #root代表的是spring-context-***.jar中的CacheExpressionRootObject，该类里有Object[] args属性及其getter方法。
@Cacheable(cacheNames = ENTERPRISE_CACHE_KEY, key = "#root.args[0]<=0? 0 : #root.args[0]")
public Result getEnterpriseByEntId1(Long enterpriseId) {...}

-------------------------------------------------

// SpEL中调用外部类函数
@Cacheable(cacheNames = ENTERPRISE_CACHE_KEY, key = "T(com.emax.common.MyUtil).foo(#root.args[0])")
public Result getEnterpriseByEntId(Long enterpriseId) {...}

// SpEL中调用外部类函数--- 设置缓存key常用的套路：当缓存key包含一个对象时，则做md5
@Cacheable(cacheNames = ENTERPRISE_CACHE_KEY, key = "T(com.emax.common.Md5Util).sign(T(com.alibaba.fastjson.JSON).toJSONString(#root.args[0]))")
public Result getEnterpriseByEntId2(UserAccountVo userAccountVo, Long enterpriseId) {...}