Why we use factory-method="aspectOf" in aspect configuration - spring

Question

I found some code in my project.By seeing that i am confused how it scanning the package.we are not mentioning aspect package com.abc.b any where.I have few question
Why aop:aspectj-autoproxy is commentout in xml file?
why is used ?
How com.abc.b package is scanned by spring or there is no need of it or It has link from 'factory-method="aspectOf"'
serviceContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:cxf="http://cxf.apache.org/core"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
http://cxf.apache.org/core http://cxf.apache.org/schemas/core.xsd" default-lazy-init="true">
<import resource="classpath:META-INF/cxf/cxf.xml" />
<import resource="classpath:META-INF/cxf/cxf-extension-soap.xml" />
<import resource="classpath:META-INF/cxf/cxf-servlet.xml" />
<!-- <aop:aspectj-autoproxy /> -->
<!-- Enable message logging using the CXF logging feature -->
<cxf:bus>
<!-- <cxf:features>
<cxf:logging/>
</cxf:features> -->
<cxf:inFaultInterceptors>
<bean class="com.flipswap.interceptor.cxf.SafeLoggingInFaultInterceptor"/>
</cxf:inFaultInterceptors>
</cxf:bus>
<context:component-scan base-package="com.abc.service.impl,">
<context:exclude-filter type="annotation" expression="org.aspectj.lang.annotation.Aspect"/>
</context:component-scan>
<bean id="eSSyncAspect" class="com.abc.b.ES" factory-method="aspectOf"/>
.
.
.
ES.java
package com.abc.b;
#Aspect
public class ES{
// some code
}

Answer 1

Unless you specify a custom instantiation model, aspects are by default singletons. That means - in case your code is properly woven -, that you can access the singleton instance of the aspect with AspectName.aspectOf().
In order for your classes to be woven by the AspectJ weaver, you need to either use compile-time/build-time weaving or load-time weaving.
In your spring configuration you are telling Spring to configure your aspect as a spring bean by telling how to access the singleton instance (through the static 'factory' method aspectOf). Spring will do the usual configuration (autowiring and any configured post-processors) on the singleton aspect instance.
aop:aspectj-autoproxy is commented out in your configuration because that would conflict with native aspectj support, as it would enable Spring AOP's dynamic proxy based AOP solution, which is very limited compared to native aspectj, and has a different mechanism to configure aspect beans than the one used in your configuration, namely through the static factory method AspectName.aspectOf().

Answer 2

In most cases, AspectJ aspects are singletons, with one instance per class loader. This single instance is responsible for advising multiple object instances.
A Spring IoC container cannot instantiate an aspect, as aspects don't have callable constructors. But it can obtain a reference to an aspect using the static aspectOf() method that AspectJ defines for all aspects, and it can inject dependencies into that aspect.
7.2.1.1. Example
Consider a security aspect, which depends on a security manager. This aspects applies to all changes in the value of the balance instance variable in the Account class. (We couldn't do this in the same way using Spring AOP.)
The AspectJ code for the aspect (one of the Spring/AspectJ samples), is shown below. Note that the dependency on the SecurityManager interface is expressed in a JavaBean property:
public aspect BalanceChangeSecurityAspect {
private SecurityManager securityManager;
public void setSecurityManager(SecurityManager securityManager) {
this.securityManager = securityManager;
}
private pointcut balanceChanged() :
set(int Account.balance);
before() : balanceChanged() {
this.securityManager.checkAuthorizedToModify();
}
We configure this aspect in the same way as an ordinary class. Note that the way in which we set the property reference is identical. Note that we must use the factory-method attribute to specify that we want the aspect "created" using the aspectOf() static method. In fact, this is locating, rather than, creating, the aspect, but the Spring container doesn't care:
<bean id="securityAspect"
class="org.springframework.samples.aspectj.bank.BalanceChangeSecurityAspect"
factory-method="aspectOf">
<property name="securityManager" ref="securityManager"/>
</bean>We don't need to do anything in Spring configuration to target this aspect. It contains the pointcut information in AspectJ code that controls where it applies. Thus it can apply even to objects not managed by the Spring IoC container.