11/14/13 spring part2－JoshS的部落格

第二堂課主要在介紹AOP 觀念

AOP(Aspect-Oriented Programming)

以圖解的方式

Btw: 此課程中會用到interface介面，而我們可以快速的建立interface介面

則是，點選 class >> 右建 >> Retuctor >> Extract Interface >> 取名稱，然後確定即可

而通常我們會把Interface的名稱 ex: SeqNumBean 變成 ISeqNum

本次課程中要把原先的程式利用 AOP 的觀念做改寫

//原先

app-config.spring.xml

SeqNumBean.java

public class SeqNumBean {
private int seqNum;

public String getSeqNum() {
String pattern = "0000";
DecimalFormat fmt = new DecimalFormat(pattern);
String seqNum = fmt.format(this.seqNum);
return seqNum;
}

public void next(){
seqNum++;
}
}

AdviceMain.java(執行檔)

public class AdviceMain {
public static void main(String[] args) {
// TODO Auto-generated method stub

ApplicationContext appCtx;
appCtx = new ClassPathXmlApplicationContext("app-config.spring.xml");
SeqNumBean seqNumBean = (SeqNumBean)appCtx.getBean("seqNumBean");

seqNumBean.next();
System.out.println("Seq Num:" + seqNumBean.getSeqNum());
seqNumBean.next();
System.out.println("Seq Num:" + seqNumBean.getSeqNum());
}
}

=================================== 更改後

BTW :AOP我真的看的好吃力!! 有點力力啦啦的~

先說明:

Spring提供了四種不同的Advice
Before :MethodBeforeAdvice
方法執行前
能修改方法的輸入參數
After :AfterReturningAdvice
方法執行後
Around :MethodInterceptor
方法執行前/後
可自行決定Target的方法是否執行
可以修改方法回傳結果
Throw :ThrowsAdvice
例外發生後

首先將 SeqNumBean 變成 ISeqNum 也就是變成interface

OK後

ISeqNum.java (interface) :

public interface ISeqNum {

public abstract String getSeqNum();

public abstract void next();

}

主要 SeqNumBean.java :

public class SeqNumBean implements ISeqNum {
private int seqNum;

   public String getSeqNum() {
  /*
    String pattern = "0000";
    DecimalFormat fmt = new DecimalFormat(pattern);
    String seqNum = fmt.format(this.seqNum);
  */
    String seqNum = String.valueOf(this.seqNum);
   return seqNum;
   }

   public void next(){
   seqNum++;
   }
}

SeqNumDateFmtAdvice.java : // (advice) Around :MethodInterceptor

public class SeqNumDateFmtAdvice implements MethodInterceptor {
private final DecimalFormat numFmt ;
private final SimpleDateFormat dateFmt;
private final String seqNumPattern;

public SeqNumDateFmtAdvice(String numPattern,
String datePattern,
String seqNumPattern){
numFmt = new DecimalFormat(numPattern);
dateFmt = new SimpleDateFormat(datePattern);
this.seqNumPattern = seqNumPattern;
}
public Object invoke(MethodInvocation invocation) throws Throwable {
// TODO Auto-generated method stub
//System.out.println("Invoke:" + invocation.getMethod());

String result = (String)invocation.proceed();
Number num =numFmt.parse(result);
result = String.format(seqNumPattern,
numFmt.format(num),
dateFmt.format(new Date()));
return result;
}
}

已上之其中

invoke()中MethodInvocation的參數包括了下一個Interceptor的資訊、被執行的方法、及方法所需之參數，其返回值是被呼叫方法的返回值。

我們仍需要一個代理物件，就可以使用org.springframework.aop.framework.ProxyFactoryBean，它需要知道代理的介面與物件，以及所要介入的Interceptor

(http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=2427 已上解釋參考)

app-config.spring.xml :

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

<bean id="targetSeqNum" class="my.test.spring3.bean.SeqNumBean"/>

<bean id="nameMatchAdvisor"
class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor">
<property name="advice">
<ref bean="fmtAdvice"/>
</property>
<property name="mappedName" value="getSeqNum"/>
</bean>

<bean id="seqNumBean"
class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="proxyInterfaces">
<value>my.test.spring3.bean.ISeqNum</value>
</property>
<property name="target">
<ref bean="targetSeqNum"/>
</property>
<property name="interceptorNames">
<list>
<value>nameMatchAdvisor</value>
</list>
</property>
</bean>

AOP 有四個重要的流程:

1.Target

2.Aspect

3.AspectJoinpoint

4.Advice

　Interceptor執行的順序是interceptorNames中設定的順序，最後是target目標物件，

可看到 target參考了 targetSeqNum ，而targetSeqNum擇連到SeqNumBean 使用下面的程式來測試一下：

SeqNumBean.java :

public class SeqNumBean implements ISeqNum {
private int seqNum;

public String getSeqNum() {
String seqNum = String.valueOf(this.seqNum);
return seqNum;
}

public void next(){
seqNum++;
}
}

最後來執行我們已上所寫好的程式

AdviceMain (執行檔):

public class AdviceMain {
public static void main(String[] args) {
// TODO Auto-generated method stub

ApplicationContext appCtx;
appCtx = new ClassPathXmlApplicationContext("app-config.spring.xml");
ISeqNum seqNumBean = (ISeqNum)appCtx.getBean("seqNumBean");

seqNumBean.next();
System.out.println("Seq Num:" + seqNumBean.getSeqNum());
seqNumBean.next();
System.out.println("Seq Num:" + seqNumBean.getSeqNum());

}
}

// 可以看到執行檔利用 seqNumBean 這個 bean (id=seqNumBean ) ，

去做 proxyInterfaces、interceptorNames、target 三個流程

// 輸出結果:

十一月 24, 2013 3:51:26 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
資訊: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@350204ce: startup date [Sun Nov 24 15:51:26 CST 2013]; root of context hierarchy
十一月 24, 2013 3:51:26 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
資訊: Loading XML bean definitions from class path resource [app-config.spring.xml]
十一月 24, 2013 3:51:26 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
資訊: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@4b4c9bfb: defining beans [targetSeqNum,nameMatchAdvisor,seqNumBean,fmtAdvice]; root of factory hierarchy
Seq Num:1124-001
Seq Num:1124-002

心得:

所以 AOP外圍架構為

1.Target

2.Aspect

3.AspectJoinpoint

4.Advice

而內為:proxyInterfaces、interceptorNames、target 三個流程

補充:

而AOP 已上方案例來看