A short introduction to INF329. Spring AOP

Transcription

1 A short introduction to INF329 Spring AOP

2 Introduction to AOP AOP is an abbreviation for aspectoriented programming Aspect-oriented programming is a new paradigm in programming, seperating functionality into aspects, not objects Aspect-oriented programming is fully integratable with object-oriented programming

3 Why AOP? Most functionality is easily divided into objects, but some is not Transactions Caching Logging Etc Common for these things is that it is things that you need, but it has nothing to do with the business logic itself, and therefore decreases the readability of the business logic code This is called cross-cutting concerns in the AOP lingo

4 What happens? The cross-cutting concerns are factored out into aspects and applied to the code in question For instance: add logging to the object in question This removes the noise from nonbusiness logic code Also, all logging code is in one place, thus removing redundancy

5 Examples of use Logging Caching Security Testing Transactions

6 AOP terms and definitions Aspect-oriented programming has its own lingo, and it s not always straight-forward: Aspect: The functionality of a crosscutting concern Joinpoint: A place in the execution where an aspect can be plugged in. In Spring AOP, this means a method call or an exception being thrown

7 AOP terms and definitions [cont.] Advice: The actual implementation of an aspect Pointcut: Ties together advice and joinpoints by specifying where the advice should be applied

8 How aspects are applied In Spring AOP, aspects are proxy-based This means that the framework uses the proxy pattern to create a proxy of the original object (called the target) and add the advice to that This is completely invisible from the business logic code Another popular AOP implementation, AspectJ, applies the aspects at compile time. This requires a special compiler

9 Advice types There are five kinds of advice supported by Spring AOP: Before advice: Add functionality that executes before a method is run After advice: Add functionality that executes after a method is run Throws advice: Add functionality that is run if an exception is thrown Around advice: Add functionality thas is executed before and after a method is run Introduction advice: Alters a class behaviour. We will not cover this in this presentation.

10 How to implement AOP in Spring With regular Spring AOP, only objects created by the container itself can be advised In Spring 2.0 and over, also AspectJ aspects are supported, enabling the programmer to advise all objects Advice is written as normal Java classes implementing one or more interfaces No need for a special compiler Pointcuts are defined in Springs XML configuration file No need to learn a new language

11 Implementing a simple before advice The advice itself is written like this: An object of this class is instanciated in Spring s config file like this: Note: The class must implement the interface MethodBeforeAdvice

12 Implementing a simple before advice [cont.] The proxy for the course object is written like this: This will cause the message entering method to be printed out every time a method of the inf100bean object is called Note: We don t use pointcuts here. The advice is applied to every method of the class.

13 After advice After advice is implemented in a very similar manner, by letting the class implement the interface AfterReturningAdvice:

14 Around advice Around advice is used when you want to add functionality before and after the method has executed The proxied method must be called explicitly with invocation.proceed() Is implemented by letting the class implement the interface MethodInterceptor

15 Throws advice Is executed if and only if the method that is advised throws an exception Note: Always rethrows the thrown exception, unless a new exception is thrown Is implemented by letting the class implement the interface MethodInterceptor

16 Applying pointcuts with advisors To be able to use pointcuts and define which methods should use which advice, we use advisors: To use the advisor, set the interceptornames value in the proxy bean to point to the advisor, not the advice

17 Wrap-up This was all we had time for today This is only a brief introduction to Spring AOP and AOP in general: It is much more! To find out more: Spring framework homepage: Manual entry about AOP: The AspectJ project: The AOP Alliance: