Skip to main content

AOP - Aspect Oriented programming

Terms:
Advice: An aspect's functionality. Aspects have a purpose - a job they're meant to do. In AOP terms, the job of an aspect is called advice. Advice  is woven into a program's execution at one or more join points.


Advice defines both the what and the when of an aspect. Spring aspects can work with five kinds of advice:
 Before—The advice functionality takes place before the advised method is
invoked.
 After—The advice functionality takes place after the advised method completes,
regardless of the outcome.
 After-returning—The advice functionality takes place after the advised method
successfully completes.
 After-throwing—The advice functionality takes place after the advised method
throws an exception.
 Around—The advice wraps the advised method, providing some functionality
before and after the advised method is invoked.

<aop:config>
<aop:aspectref="audience">
<aop:pointcutid="performance"expression=
"execution(* com.springinaction.springidol.Performer.perform(..))"
/>
<aop:before
pointcut-ref="performance"
method="takeSeats" />
<aop:before
pointcut-ref="performance"
method="turnOffCellPhones"/>
<aop:after-returning
pointcut-ref="performance"
method="applaud" />
<aop:after-throwing
pointcut-ref="performance"
method="demandRefund" />
</aop:aspect>
</aop:config>





Join Points,
A join point is a point in the execution of the application where an aspect can be plugged in. This point could be a method being called, an exception being thrown, or even a field being modified.

PointCuts,

If advice defines the what and when of aspects, then pointcuts define the where. A
pointcut definition matches one or more join points at which advice should be woven.


Aspects,
An aspect is the merger of advice and pointcuts. Taken together, advice and pointcuts define everything there is to know about an aspect - what it does and where an when it does it.

Introductions,
An introduction allows you to add new methods or attributes to existing classes.

Weaving
Weaving is the process of applying aspects to a target object to create a new proxied object. Spring Aspects are woven in sometime during the execution of the application. Typically, Spring AOP Container will dynamically generate a proxy object that will delegate to the target object while weaving in the aspect in Runtime.


Annotating aspects,
A key feature introduced in ApsectJ5 is the ability to use annotations to create aspects.
Prerequisite:  <aop:aspectj-autoproxy/>



@Aspect
public classAudience{
@Pointcut(
"execution(* com.springinaction.springidol.Performer.perform(..))")
public voidperformance(){
}
@Before("performance()")
public voidtakeSeats(){
System.out.println("Theaudienceistakingtheirseats.");
}
@Before("performance()")
public voidturnOffCellPhones(){
System.out.println("Theaudienceisturningofftheircellphones");
}
@AfterReturning("performance()")
public voidapplaud(){
System.out.println("CLAPCLAPCLAPCLAPCLAP");
}
@AfterThrowing("performance()")
public voiddemandRefund(){
System.out.println("Boo!Wewantourmoneyback!");
}

Comments

Popular posts from this blog

Quicksort implementation by using Java

 source: http://www.algolist.net/Algorithms/Sorting/Quicksort. The divide-and-conquer strategy is used in quicksort. Below the recursion step is described: 1st: Choose a pivot value. We take the value of the middle element as pivot value, but it can be any value(e.g. some people would like to pick the first element and do the exchange in the end) 2nd: Partition. Rearrange elements in such a way, that all elements which are lesser than the pivot go to the left part of the array and all elements greater than the pivot, go to the right part of the array. Values equal to the pivot can stay in any part of the array. Apply quicksort algorithm recursively to the left and the right parts - the previous pivot element excluded! Partition algorithm in detail: There are two indices i and j and at the very beginning of the partition algorithm i points to the first element in the array and j points to the last one. Then algorithm moves i forward, until an element with value greater or equal

Live - solving the jasper report out of memory and high cpu usage problems

I still can not find the solution. So I summary all the things and tell my boss about it. If any one knows the solution, please let me know. Symptom: 1.        The JVM became Out of memory when creating big consumption report 2.        Those JRTemplateElement-instances is still there occupied even if I logged out the system Reason:         1. There is a large number of JRTemplateElement-instances cached in the memory 2.     The clearobjects() method in ReportThread class has not been triggered when logging out Action I tried:      About the Virtualizer: 1.     Replacing the JRSwapFileVirtualizer with JRFileVirtualizer 2.     Not use any FileVirtualizer for cache the report in the hard disk Result: The japserreport still creating the a large number of JRTemplateElement-instances in the memory        About the work around below,      I tried: item 3(in below work around list) – result: it helps to reduce  the size of the JRTemplateElement Object        

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold  highlighted in example below) which resolve the problems.   example: <band height="20" splitType="Stretch" > <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/>