Java Reference
In-Depth Information
Logging is not the concern of
BookServiceImpl
. For logging, create an aspect as illustrated in
Listing 5-20 that will be woven into the
BookService
object, providing the logging wherever needed.
Listing 5-20. Aspect for Logging
1. package com.apress.aop;
2.
3. public class LoggingAspect {
4. public void logBefore() {
5.
6. System.out.println("Before calling getAllBooks");
7. }
8.
9. public void logAfter() {
10. System.out.println("After calling getAllBooks");
11. }
12. }
13.
Line 3
:
LoggingAspect
is a simple class with two methods.
Line 4
: The
logBefore()
method that should be invoked before
getAllBooks()
is called.
Line 9
: the
logAfter()
method that should be invoked after the
getAllBooks()
is called.
The
LoggingAspect
does its job without the
BookServiceImpl
asking it to do so. Furthermore,
because the
BookServiceImpl
does not need to know about the
LoggingAspect
, you are not
required to inject the
LoggingAspect
into the
BookServiceImpl
. This removes the unneeded
complexity from the
BookServiceImpl
code of having to inject
LoggingAspect
and having to check
whether
LoggingAspect
is null. As you may have noticed,
LoggingAspect
is a POJO. It becomes
an aspect when it is declared as an aspect in the Spring context.
LoggingAspect
can be applied
to the
BookServiceImpl
without the
BookServiceImpl
needing to explicitly call on it. In fact,
BookServiceImpl
remains totally unaware of
LoggingAspect
's existence. To make
LoggingAspect
work as an aspect, all you need to do is declare it as one in the Spring configuration file.
Listing 5-21 illustrates the application context XML file that declares
LoggingAspect
as an aspect.
Listing 5-21. Configuration File
1. <?xml version="1.0" encoding="UTF-8"?>
2. <beans xmlns="
http://www.springframework.org/schema/beans
"
3. xmlns:xsi="
http://www.w3.org/2001/XMLSchema-instance
"
xmlns:context=
4. xmlns:aop="
http://www.springframework.org/schema/aop
"
5. xsi:schemaLocation="
http://www.springframework.org/schema/beans
11.
