切面编程的实现

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1、面向切面的定义自行百度

2、面向切面编程的应用场景自己想象，大概就是日志之类的地方

3、上面两句话基本是废话

实现方式一，在XML中声明切面

1、编写一个原始类

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package com.hsb.beans;
import org.springframework.stereotype.Repository;
@Repository
public class Perform {
public void show(){
System.out.println(”message from Perform.show()”);
}
}

package com.hsb.beans;import org.springframework.stereotype.Repository;@Repositorypublic class Perform {    public void show(){        System.out.println("message from Perform.show()");    }}

本例中show()方法就是切点。在一个大型项目中，许多个切点构成了切面，这些切面实际上是为了某些共同的东西而成为一个面的。
2、编写一个切面类

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package com.hsb.aop;
import org.aspectj.lang.ProceedingJoinPoint;
public class Audience {
public void beforeShow(){
System.out.println(”message from beforeShow”);
}
public void afterShow(){
System.out.println(”message from afterShow”);
}
public void around(ProceedingJoinPoint joinpoint){
System.out.println(”message from Start around”);
long start = System.currentTimeMillis();
try {
joinpoint.proceed();
} catch (Throwable e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println(”message from End around total : ”+(end-start)+“ ms”);
}
}

package com.hsb.aop;import org.aspectj.lang.ProceedingJoinPoint;public class Audience {    public void beforeShow(){        System.out.println("message from beforeShow");    }    public void afterShow(){        System.out.println("message from afterShow");    }    public void around(ProceedingJoinPoint joinpoint){        System.out.println("message from Start around");        long start = System.currentTimeMillis();        try {            joinpoint.proceed();        } catch (Throwable e) {            e.printStackTrace();        }        long end = System.currentTimeMillis();        System.out.println("message from End around total : "+(end-start)+" ms");    }}

注意代码中的joinpoint.proceed()，这句话就是实际调用切点方法，也就是本例中的show()。如果切面类中定义了around通知，通知一定要加上这句话，否则要切点方法不会被调用！此处应该是一个坑，一定要记住，免得后面找bug到处都找不到。

3、配置XML

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<?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:aop=“http://www.springframework.org/schema/aop”
xmlns:tx=“http://www.springframework.org/schema/tx” xmlns:context=“http://www.springframework.org/schema/context”
xsi:schemaLocation=”http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd”
default-lazy-init=“true”>
<context:component-scan base-package=“com.hsb.beans” />
<bean id=“audience” class=“com.hsb.aop.Audience” />
<aop:config>
<aop:aspect ref=“audience”>
<aop:pointcut expression=“execution(* com.hsb.beans.Perform.show(..))”
id=“performance” />
<aop:before method=“beforeShow” pointcut-ref=“performance” />
<aop:after method=“afterShow” pointcut-ref=“performance” />
<aop:around method=“around” pointcut-ref=“performance” />
</aop:aspect>
</aop:config>
</beans>

<?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:aop="http://www.springframework.org/schema/aop"    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"    xsi:schemaLocation="http://www.springframework.org/schema/beans                           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd                          http://www.springframework.org/schema/aop                           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd                          http://www.springframework.org/schema/tx                           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd                          http://www.springframework.org/schema/context                           http://www.springframework.org/schema/context/spring-context-3.0.xsd"    default-lazy-init="true">    <context:component-scan base-package="com.hsb.beans" />    <bean id="audience" class="com.hsb.aop.Audience" />    <aop:config>        <aop:aspect ref="audience">            <aop:pointcut expression="execution(* com.hsb.beans.Perform.show(..))"                id="performance" />            <aop:before method="beforeShow" pointcut-ref="performance" />            <aop:after method="afterShow" pointcut-ref="performance" />            <aop:around method="around" pointcut-ref="performance" />        </aop:aspect>    </aop:config></beans>

注意，上面的<bean id=”audience” class=”com.hsb.aop.Audience” />将切面类生命为一个bean，而<aop:config></aop:config>声明中引用了这个bean.简单解释一下<aop:config>声明中各句的意思。配置声明的时候，一定注意使用英文字符进行配置，不然会报很多稀奇古怪的错误，大致就是说切面无法使用或者其他什么的。

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<aop:pointcut expression=“execution(* com.hsb.beans.Perform.show(..))”
id=“performance” />

<aop:pointcut expression="execution(* com.hsb.beans.Perform.show(..))"                id="performance" />

声明了一个切点（pointcut），后面声明的通知会引用。

通知一共有五种分别是<aop:before />、<aop:after />、<aop:after-returning />、<aop:after-throwing />、<aop:around />。根据其字面意思大概就能懂其应用场景，而around上面已经说过了，标识出切点位置，在切点前后做某些工作。

4、测试

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package com.hsb.dao;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import com.hsb.beans.Perform;
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({“classpath*:**/applicationContext.xml”,“classpath*:**/springmvc-servlet.xml”})
public class PerformTests {
@Autowired
private Perform perform;
@Test
public void testShow() {
perform.show();
}
}

package com.hsb.dao;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.test.context.ContextConfiguration;import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import com.hsb.beans.Perform;@RunWith(SpringJUnit4ClassRunner.class)@ContextConfiguration({"classpath*:**/applicationContext.xml","classpath*:**/springmvc-servlet.xml"})public class PerformTests {    @Autowired    private Perform perform;    @Test    public void testShow() {        perform.show();    }}

上面的代码使用自动注入生成一个Perform实例，在测试方法中调用切点方法show().

5、Console打印结果

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九月 05, 2016 9:54:03 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from file [D:\PractiseForWork\WorkSpace\HelloMaven\target\classes\applicationContext.xml]
九月 05, 2016 9:54:04 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.GenericApplicationContext@6e3c1e69: startup date [Mon Sep 05 21:54:04 CST 2016]; root of context hierarchy
message from beforeShow
message from Start around
message from Perform.show()
message from End around total : 38 ms
message from afterShow

九月 05, 2016 9:54:03 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from file [D:\PractiseForWork\WorkSpace\HelloMaven\target\classes\applicationContext.xml]九月 05, 2016 9:54:04 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.GenericApplicationContext@6e3c1e69: startup date [Mon Sep 05 21:54:04 CST 2016]; root of context hierarchymessage from beforeShowmessage from Start aroundmessage from Perform.show()message from End around total : 38 msmessage from afterShow

从Console的打印结果中，我们可以猜测出五种通知的具体用法

6、Maven工程一定要添加依赖

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<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
<version>1.6.12</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
<version>1.6.12</version>
</dependency>

                <dependency>            <groupId>org.aspectj</groupId>            <artifactId>aspectjrt</artifactId>            <version>1.6.12</version>        </dependency>        <dependency>            <groupId>org.aspectj</groupId>            <artifactId>aspectjweaver</artifactId>            <version>1.6.12</version>        </dependency>

如果不添加上述依赖，极有可能会测试报错。

实现方式二，注解切面

1、编写一个原始类

[java] view plain copy

print?

package com.hsb.beans;
import org.springframework.stereotype.Repository;
@Repository
public class Perform {
public void show(){
System.out.println(”message from Perform.show()”);
}
}

package com.hsb.beans;import org.springframework.stereotype.Repository;@Repositorypublic class Perform {    public void show(){        System.out.println("message from Perform.show()");    }}

2、编写一个切面类

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print?

package com.hsb.aop;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;
@Aspect
@Component
public class Audience {
@Pointcut(“execution(* com.hsb.beans.Perform.show(..))”)
public void performance() {
}
@Before(“performance()”)
public void beforeShow() {
System.out.println(”message from beforeShow”);
}
@After(“performance()”)
public void afterShow() {
System.out.println(”message from afterShow”);
}
@Around(“performance()”)
public void around(ProceedingJoinPoint joinpoint) {
System.out.println(”message from Start around”);
long start = System.currentTimeMillis();
try {
joinpoint.proceed();
} catch (Throwable e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println(”message from End around total : ” + (end - start)
+ ” ms”);
}
}

package com.hsb.aop;import org.aspectj.lang.ProceedingJoinPoint;import org.aspectj.lang.annotation.After;import org.aspectj.lang.annotation.Around;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Before;import org.aspectj.lang.annotation.Pointcut;import org.springframework.stereotype.Component;@Aspect@Componentpublic class Audience {    @Pointcut("execution(* com.hsb.beans.Perform.show(..))")    public void performance() {    }    @Before("performance()")    public void beforeShow() {        System.out.println("message from beforeShow");    }    @After("performance()")    public void afterShow() {        System.out.println("message from afterShow");    }    @Around("performance()")    public void around(ProceedingJoinPoint joinpoint) {        System.out.println("message from Start around");        long start = System.currentTimeMillis();        try {            joinpoint.proceed();        } catch (Throwable e) {            e.printStackTrace();        }        long end = System.currentTimeMillis();        System.out.println("message from End around total : " + (end - start)                + " ms");    }}

@Aspect将此类声明为切面类，@Component将此类声明为bean放到spring容器中，@Pointcut将下面的performance声明为一个切点，并将Perform中的show()方法进行了关联。execution(* com.hsb.beans.Perform.show(..))的意思是，执行此方法时，忽略返回值，参数类型和个数忽略。还可以更加简写，用于匹配合适的方法，譬如对Perform类的全部方法进行匹配就是com.hsb.beans.Perform.*。

3、配置xml

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<?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:aop=“http://www.springframework.org/schema/aop”
xmlns:tx=“http://www.springframework.org/schema/tx” xmlns:context=“http://www.springframework.org/schema/context”
xsi:schemaLocation=”http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd”
default-lazy-init=“true”>
<context:component-scan base-package=“com.hsb.*” />
<aop:aspectj-autoproxy proxy-target-class=“true”/>
</beans>

<?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:aop="http://www.springframework.org/schema/aop"    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"    xsi:schemaLocation="http://www.springframework.org/schema/beans                           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd                          http://www.springframework.org/schema/aop                           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd                          http://www.springframework.org/schema/tx                           http://www.springframework.org/schema/tx/spring-tx-3.0.xsd                          http://www.springframework.org/schema/context                           http://www.springframework.org/schema/context/spring-context-3.0.xsd"    default-lazy-init="true">    <context:component-scan base-package="com.hsb.*" />    <aop:aspectj-autoproxy proxy-target-class="true"/></beans>

可以看见此处就没有使用<aop:config />声明，而是使用<aop:aspectj-autoproxy proxy-target-class=”true” />。这句话的意思是自动在spring上下文中创建一个AnnotationAwareAspectJAutoProxyCreator类，它会自动代理一些bean，这些bean的方法需要与使用@Aspect注解的bean中所定义的切点相匹配，而这些切点又是使用@Pointcut注解定义出来的。proxy-target-class=”true”的意思是使用基于类的代理使用cglib库，如果为false则使用jdk自带的基于接口的代理

4、测试

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package com.hsb.dao;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import com.hsb.beans.Perform;
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({“classpath*:**/applicationContext.xml”,“classpath*:**/springmvc-servlet.xml”})
public class PerformTests {
@Autowired
private Perform perform;
@Test
public void testShow() {
perform.show();
}
}

package com.hsb.dao;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.test.context.ContextConfiguration;import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import com.hsb.beans.Perform;@RunWith(SpringJUnit4ClassRunner.class)@ContextConfiguration({"classpath*:**/applicationContext.xml","classpath*:**/springmvc-servlet.xml"})public class PerformTests {    @Autowired    private Perform perform;    @Test    public void testShow() {        perform.show();    }}

5、Console打印结果

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九月 05, 2016 10:24:46 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from file [D:\PractiseForWork\WorkSpace\HelloMaven\target\classes\applicationContext.xml]
九月 05, 2016 10:24:47 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.GenericApplicationContext@6e3c1e69: startup date [Mon Sep 05 22:24:47 CST 2016]; root of context hierarchy
message from Start around
message from beforeShow
message from Perform.show()
message from End around total : 39 ms
message from afterShow

九月 05, 2016 10:24:46 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from file [D:\PractiseForWork\WorkSpace\HelloMaven\target\classes\applicationContext.xml]九月 05, 2016 10:24:47 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.GenericApplicationContext@6e3c1e69: startup date [Mon Sep 05 22:24:47 CST 2016]; root of context hierarchymessage from Start aroundmessage from beforeShowmessage from Perform.show()message from End around total : 39 msmessage from afterShow

如上所示，完全是一样的效果。可以看出使用注解减少了很多工作，不容易出错，各个组件间的耦合度降低了。试想，如果一个大型项目中有很多切面，切点，如果全部去xml中配置，将会是一项极为艰苦的工作，但是如果使用注解就可以做很少的工作完成这一切。

后记一、使用注解时一定要使用@component或者@Repository、@Controller、@Service中一个去声明，将切面类放入到spring容器中，不然就去xml中显式写一个bean，不然的话就会报错，无法实现切面功能。

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