Spring Tutorial 28 - Pointcuts and Wildcard Expressions

hi and welcome to this tutorial the last tutorial was about writing an advice so we wrote an advice method inside an aspect and we use aspect oriented programming to actually call this advice code whenever a particular target method is run so this is a very simple advice and a very simple configuration here we have a before annotation that tells before which method this advice has to run so we used this particular string in order to configure that method which we are interested in the target method now we ended the tutorial with one particular problem that I showed you we have used this before annotation to make this advice run before a public string it name is called we originally intended this advice to be called before the get name of the circle class is called but now what what's happening is since we have not made any mention of the circle class over here it's this advice is running for every call to every public string get name no matter where it is even if it's in the triangle class you know in the triangle we have a public street name so even when this method is called that advises call so this is one problem that we will try to correct we want to make this advisor not only for a get name of a circle and this is one of the things we look at other ways in which we can configure this particular definition of the target method so in order to restrict this to a particular class or a particular object what we need to do is we need to provide information about that class in this string so we know that we want this advice to get executed before the execution of this method so in order to make this restricted to a particular class what we need to do is we need to give the class name over here so since I want this advice to run before a get name off a circle class all I need to do is before the getname method that I'm writing I need to write the name of the circle class with the package name so this would be org dot Koscheck Georgia our brains dot model dot so cool duck it me so all I'm doing this I'm specifying the class for which this getname method belongs to so that I can give more information to spring about which give name I'm actually interested in so now that I have specified this spring is going to look for this particular pattern and it's going to match only if a get name off the circle class with this particular package is executed so if a get name with the same signature public string get name of another class is executed like a triangle here this will not run so let's quickly test that out save this and let's run this class now I'm calling shape service start get circle target name now this advice has to run so here you see circle name is printed but the advice is run so now if I change this to a triangle running the get name for triangle ideally the advice should not run and it does not it just prints the triangle name but here even though the gate name is run the advice is not kicking in and executing this so this is the way we can restrict the method and you know the advice can be applied only to particular methods that we are actually interested in okay so now that you've covered how we can restrict this I'm going to show you two different ways in which we can configure this now the two scenarios that I'm going to show you is what if you want one particular advice to be applied to different methods after that's the point of an adviser's net we talked about cross-cutting concerns and how one piece of code that applies across different points in the execution of your code needs to be isolated out so now that I've isolated a cross-cutting concern I need to be able to apply this cross-cutting concern across different points and we look at a way to do with that and the second thing that I'm going to show you is the the other way now say I have one particular point in the execution of my code where I want different advise methods to get executed now how would I do that so these two things are something to build cover in this tutorial so let's look at the first thing one advice applied to different points in the execution the way to do that is of course you can replicate this say you want another method so you want to apply this for the triangle you can just replicate this write another method and then apply this just change this to triangle then that would work but then you are again you know duplicating the code so the way to do this is by using wildcards now we saw one way we actually did it I mean we didn't we didn't intend to do it but it actually happened now this applied to all methods of the code which have a public string gate name as a signature so this is actually what actually happened with an intent for that to happen but we did implement an advice method across different points in the execution so as long as different points in the execution of the code have a public string get name one advice can be applied to different methods in your code now there are other reason which we can configure it now let's say I want this advice to be applied to all Gators in the code no matter where they are we have a get name here right so I have a good name for a circle and I have a get name for the triangle so this expression is going to apply this advice to all public string get names but let's say I want this advice to be applied to all get us whether it's a good name or a get anything else I want this advice to be applied so notice here in the shape service I have a get circle another get triangle now let's say I want this advice to be applied to as well so the way I can do that is by using a wild card now instead of specifying the gate Nemo here what I'll do is I'll say get star so what I'm saying here is get anything so whatever be the method that starts with a gate and then it has a public string I want this to be applied so this would work for all Gators that are done a string but notice here in the shape service I'm not returning a string so the gate triangle is returning a triangle and a good circle is returning a circle so what I'll do is I'll remove the string and I'll add an a star over here as well so this is another wild card so no matter any method if as long as it starts with a get and it no matter what it returns I'm putting a start here so irrespective of the return type as long as a method there is a public method and it starts with the words G with the letters G et I want this advice to be applied so this is the same expression but I've used wildcards here so I can apply this advice across different points now let's save this and see what happens now the ideally what should happen is this get star should apply to a get circle get name so it will happen twice so in my yupi get triangle let me change this to a circle and save this so now the get circle will trigger the first coil to this aspect so it is a public irrespective the return type the method starts with GE t so the first call is triggered and then a gift name is called now again this satisfies this expression it's a public key respective the return type the method starts with GE t so again it's going to get called so now this single line of code a shape service target circle dot get name is going to return in two calls this logging advice now let's see that in action that you see you have two coils so the first coil is for the gate circle the second coil is for the gate name now even if I change this to a triangle it's going to result in the same output because we have not specified the class all we are saying is any Kitter it respect to the return type just make sure this advice is called so we have to get us that our call here the gate triangle and the gate name so again this is going to result in two calls to the advice so you can use different permutations and combinations say you want you don't you do not want to specify the you know the whether it's a public or a private you can just remove this so what we are seeing is any return type as long as it has a GED as the first three letters of the method execute this locking advice so there are different ways in which we can specify these wild cards you can specify a wild card here as well so what we did earlier was without this wild card what we are saying is this method should not take any parameters there are no arguments to this method so that's what we have denoted here by not specifying anything over here but now let's say you have a getter method which takes in an argument and you want this advice to be applied for that as well then what you do is you specify a wild card over here so that would mean that as long as there is an argument some some argument then it's going to get applied for all Gators that have some argument now if you want this advice to be applied for all Gators irrespective whether they have arguments or not then what you do is you add a dot dot over here so a dot dot here means that it can be zero arguments or it can be any number of arguments it's going to match this and the logging advice is called so in summary what we do is you specify star or the asterisks for any any wild card that you want to apply for either the return type or the method name and as far as the parameters are concerned you apply the dot dot expression for any match of you know zero or more arguments and you apply a star for one or more arguments and if you remove this you just have open close that means that you're matching for zero arguments so this is this gives you a lot of flexibility actually you can mix and match this to catch a lot of signatures and specifically apply for the other points that you are actually interested in so this is the weight in which you can apply single advise methods to different points in the execution of your code and of course you can use the you know the package name to get more control so he can go say I have org the cross shape dot Java brain started model dot star dot get started so what I'm doing is I'm saying all classes inside this modal package then a method that starts with the gate so you can you can mix and match this so you can you know get complete control over what methods you're actually interested in and for what methods this advice has to apply ok so now lets me remove this okay so now we have looked at ways in which we can apply a single advice to multiple points in the execution now what if you know we are looking at the other way now you have one point in the execution of your code anyone multiple pieces of advice to get executed one way we can do this is again by using different methods and repeating this expression now let's say for all Gators I want a logging advice to get executed and I want one more advice to get excreta let me at that public void let's say second advice so I'll again print something out second advice is executed now I want these two advised methods to get executed on all Gators so it's very simple all I need to do is I need to copy this and biggest this here right so it's going to happen both these methods are going to get executed for all the execution of all the methods that match these patterns but if you have a lot of methods like this you will be repeating this expression now this is a very simple expression but let's say it's fairly complex you have specified the package name the return type and a whole lot of configuration if you had if you have a lot of methods a lot of advice methods then you would have to repeat this expression and you have to repeat this before annotation for all those methods now there is a shortcut for this now the way you can do this is by defining what are called as point cuts point cut is AUP terminology again for all the points in the execution of your code where you want this advise method to cut in so the point where you want the method to cut in there's a point cut so this star get star of no arguments is a point cut for second advice the same way this is a point cut for the logging advice so what we can do is since you have the same pointer that are being used by two different advise methods what you can do is you can define a point cut separately and put this expression over here and then when you are configuring your advice you just say hey I already defined a point cut over there so that's where you want this advice to run and again through the same thing you can just refer to that point cut and then that point cut will have this expression you don't have to put this expression on all your advice methods so let's do that now I'll define a point cut by using the ACT point cut annotation that point cut annotation takes an expression it's same as the before it takes an expression about where the actual point cut needs to take place so I'll just copy this and paste this over here so this is it's a simple point cut that says on all execution of all getters this point that needs to be applied now I can't just leave an annotation like this the annotation has to annotate something so what I'll do is I'll write a method over here let's say all Gators now this is a dummy method all Gators is a dummy method it does not have any code inside it but what this does is it holds a point cut expression we see here this point cut is applied to all Gators now that I have defined this pointer over here I don't have to use this expression everywhere I want an advice to get applied so I have this expression over here and over here logging advice and second advice I don't have to put this expression over here what I need to do is I need to say before this all Gators what I'm saying is he already have defined this point get expression over here so that's what I want this advice to use so all I do is I'll change this expression to all Gators and even for this advice so this advice you know is annotated with before of all Gators so all that it does is it checks for the all Gators method and it takes this expression and the same thing for the second advice so this saves you typing as well as make sure that you type your expression only once and then you can use that expression across different points so let's let's run this now let's see what happens so here you see this both these advisors are executing twice so this is for the first one is for the get triangular the second one is for the get me and that's happening because it's running for all Gators now the all Gators has the pattern that matches for the Gators and now I do not have to use the pattern for each and every advice I just refer to this method which has the pointed expression so this is the way in which you can use a particular expression and match multiple advice methods so so we have looked at two ways in which you can configure point get expressions one is if you one the same advice to get applied to different points and different point cuts then all you do is you use wildcards or you write your expressions whether it matches different points and then the second thing if you want one particular point cut expression to get applied to different advice methods what what you do is you use a point cut annotation and then annotate a dummy method and then you can use a dummy method as a reference for all your before annotation so that no matter how many advise methods you have those advise methods will point to this point get expression and then it's going to apply just like you it's almost as if you have used this expression in each of your advice methods only thing is you're just referring to one consolidated place in which you have your point cut expression

Channel: Java Brains

Views: 189,325

Keywords: spring, framework, aop, aspect, oriented, programming, dependency, injection, inversion, control, build, apache, tutorial, technology, computers, java, free, j2ee, ee, educational, eclipse, tomcat, javabrains, brains, koushik

Id: h7IdaLybg9A

Length: 19min 24sec (1164 seconds)

Published: Mon Aug 22 2011