9B3.SpEl Sample

Spring Expression Language (SpEL) is used in Cacheable, DoubleKill's Aop scenario.

9B3.1.Use in Aop

@Cacheable and @DoubleKill have the following built-in variables based on the MethodBasedEvaluationContext

• #root.method - the method being Aop
• #root.target - the method's execution target
• #root.caches - the affected cache (DK none)
• #root.methodName - method.getName
• #root.targetClass - target.getClass
• #root.args - all parameters of method
• #root.args[0], #p0 or #a0, all for the 1st argument, 0-based
• #paraName - used as parameter name, via ParameterNameDiscoverer
• #result - the result of the call (DK none)

9B3.2.Common Use

Special references and formats

• #this - refers to the current evaluation object
• #root - refers to the root context object
• @foo - lookup bean named foo
• T(xxx) - refers to type
• #{ ... } - expression templating

null check and default values @Value("#{systemProperties['pop3.port'] ?: 25}")

• null?:'Unknown' - name != null ? name : "Unknown"
• PlaceOfBirth?.City - PlaceOfBirth.City != null ? PlaceOfBirth.City : null

stream like filter and map operations

• Members.?[Nationality == 'Serbian'] - Members.filter
• Members.![placeOfBirth.city] - Members.map(it.placeOfBirth.city)

General list and object navigation

• Members[0].Inventions[6]
• Officers['president'].PlaceOfBirth.City

Literal Constructed List

• {1,2,3,4} - [1,2,3,4] of List<Integer>
• {{'a','b'},{'x','y'}} - [['a','b'],['x','y']] of List<List<String>>