Spring AOP Summary part1
This paper will make a summary about how to use AOP & on where we should pay attention。before we start talk about AOP, i should introduce the base environment for our AOP practice.
Environment Requirements : Spring 4.3.X serial package, Idea_2018 , Java8, Tomcat8.5, if you prepare all those, Here we goes:
Step 1：add dependecies spring-aop spring-aspects here is the draft of the pom file.
4.0.0
palette.song
gotta
1.0-SNAPSHOT
war
javax.servlet
javax.servlet-api
3.1.0
org.springframework
spring-web
4.3.2.RELEASE
org.springframework
spring-webmvc
4.3.2.RELEASE
org.springframework
spring-aop
4.3.2.RELEASE
org.springframework
spring-aspects
4.3.2.RELEASE
step2: configure the application.xml like this:
step3： write the aspect class & set the point cut.
package com.cloud.Aspects;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
@Aspect
@Service
public class HelloAspects {
@Pointcut("execution(* com.cloud.song.HelloWorld.sayHello(..))")
public void pointCut(){
}
@Before("pointCut()")
public void before(JoinPoint joinPoint){
System.out.println("Hello World! pointCut");
}
@AfterThrowing(pointcut = "pointCut()",throwing = "throwable")
public void afterThrowing(Throwable throwable){
}
@After("pointCut()")
public void after(){
}
}step 4 run this web program on tomcat server
when you send a request by a http client like curl or python rquests or a browser you will see a console print, that shows out aspect works. and please notice the project structure and the usages of aop or correctly called aspects. let`s conclude it.
step 5:
How to understand @Pointcut("execution(* com.cloud.song.HelloWorld.sayHello(..))"）？well, it the method we will cut or the point we shall cut. it can be accurate to a method or method name contains certain words or the class or a package or even the whole project. if you know a lot about regrex, you can skip this section.
first, the first char * represent the value can be return by the method, '*' tells the aspects every return method even the void method should included in our point cut , you can assign a precise return to point cut a method. for example (void com.cloud.song.HelloWorld.sayHello(..)), once you do it , the same name method but return int or long or other return type won`t be cut. by the way, leave a space between * and com
second, the package name & class name & method name, you can replace the by * or . which * replace all the chars & . only replace one chars. but you can`t ingore the split point '.' between packages. if you want point cut all the method, (* *..*.*(..)))
thrid, also you can composite some point use '||' you can write the point cut path or just write the point cut method. for example
package com.cloud.Aspects;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
@Aspect
@Service
public class HelloAspects {
@Pointcut("execution(void *..*.*(..))")
public void pointCut(){
}
@Pointcut("execution(int com.*..*(..))")
public void point(){
}
@Before("pointCut() || point()")
public void before(JoinPoint joinPoint){
System.out.println("Hello World! pointCut");
}
@AfterThrowing(pointcut = "pointCut()",throwing = "throwable")
public void afterThrowing(Throwable throwable){
}
@After("pointCut()")
public void after(){
}
}
finally, the (..) expresses that zero or more params may deliver by the method.
next article i will write the annotions about aop like @after @before and so on. in the serial ending part, i will complain the drawbacks & advantanges about aop on different use situtions.