TraceInterceptor is Interceptor to handle trace processing as "Crosscutting Concern".
As an example, an aspect is applied to the following Service class.

module Example
  class Service
    s2comp
    def add(a, b) {
      puts "#{self.class.superclass.name}.add called."
      return a + b
    end
  end
end

Please create the following executable files.

require 's2container'
require 'example'

Seasar::Container::S2ApplicationContext.aspect(:pattern => Example::Service, :interceptor => Seasar::Aop::Interceptor::TraceInterceptor.new)
container = Seasar::Container::S2ApplicationContext.create
service   = container->get(Service)

p service.add(2, 3)

when you execute above script, when the add method of the service class was carried out, TraceInterceptor outputs log.

% ruby run.rb
D, [2009-01-01] DEBUG -- Seasar::Aop::Interceptor::TraceInterceptor: before : Example::Service.add([2, 3])
Example::Service.add called.
D, [2009-01-01] DEBUG -- Seasar::Aop::Interceptor::TraceInterceptor: after  : Example::Service.add([2, 3]) : 5 : 0.002727
5
%

When implementing custom-made Interceptor, please create the class which implements the call method. Let's create following Interceptor as an example.

module Example
  class SampleInterceptor
    def call(invocation)
      puts 'Before'            # <-- Processing before calling following Interceptor or a following actual method
      result = invocation.proceed
      puts 'After'             # <-- Processing after calling following Interceptor or a following actual method
      return result
    end
  end
end

Execution of MethodInvocation.proceed method will call following Interceptor or a following actual method. If two or more Aspects are defined as one component, as-follows execution is carried out.

The instance for an aspect, method, method arguments, etc. are acquirable through MethodInvocation passed by the argument of Interceptor::invoke method.