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鲁春利的工作笔记,好记性不如烂笔头
面向方面的编程(AOP) 是一种编程范式,旨在通过允许横切关注点的分离,提高模块化。
package com.invicme.apps.aop.proxy; import org.apache.log4j.Logger; /** * * @author lucl * * 数学计算实现类 * */ public class ArithmeticCalculateImpl implements ArithmeticCalculate { private static final Logger logger = Logger.getLogger(ArithmeticCalculateImpl.class); private int i = 0; private int j = 0; public ArithmeticCalculateImpl () { this(0, 0); } public ArithmeticCalculateImpl (int i, int j) { this.i = i; this.j = j; } @Override public int add(int i, int j) { logger.info("The method add was invoke with args [" + i + ", " + j + "]"); int sum = i + j; logger.info("The method add ends with result [" + sum + "]"); return sum; } @Override public int div(int i, int j) throws DivisorIsZeroException { logger.info("The method div was invoke with args [" + i + ", " + j + "]"); if (j == 0) { throw new DivisorIsZeroException("除数不可为0"); } int result = i / j; logger.info("The method div ends with result [" + result + "]"); return result; } @Override public String validateNum(String level, int i) { logger.info("The method validateNum was invoke with args [" + level + ", " + i + "]"); String result = this.getMsg(i); logger.info("The method validateNum ends with result [" + result + "]"); return result; } private String getMsg (int i) { if (i > 0) { return "正数"; } return "负数"; } }
对于类ArithmeticCalculateImpl的日志通过在方法中加入logger.info来记录的,存在大量的冗余代码,特别是如果在项目开发阶段未通过这种方式记录日志,那么希望记录日志时需要修改代码加入日志逻辑(OOP开发模式)。
AOP为开发者提供一种进行横切关注点分离并织入的机制,把横切关注点分离,然后通过某种技术织入到系统中,从而无耦合的完成了我们的功能。
Aspect(切面):指横切性关注点的抽象即为切面,它与类相似,只是两者的关注点不一样,类是对物体特征的抽象,而切面横切性关注点的抽象.
Joinpoint(连接点):所谓连接点是指那些被拦截到的点。在Spring中,这些点指的是方法,因为spring只支持方法类型的连接点,实际上Joinpoint还可以是Field或类构造器。
Pointcut(切入点):所谓切入点是指我们要对哪些Joinpoint进行拦截的定义。
Advice(通知):所谓通知是指拦截到Joinpoint之后所要做的事情。通知分为前置通知,后置通知,异常通知,最终通知,环绕通知。
Target(目标对象):代理的目标对象。
Weave(织入):指将aspects应用到target对象并导致proxy对象创建的过程称为织入。
Introduction(引入):在不修改类代码的前提下, Introduction可以在运行期为类动态地添加一些方法或Field。
Spring提供了4种实现AOP的方式:
经典的基于代理的AOP
@AspectJ注解驱动的切面
纯POJO切面
注入式AspectJ切面
前三种都是Spring基于代理的AOP变体,因此Spring对AOP的支持局限于方法拦截。如果AOP需求超过了简单方法的拦截范畴(如构造器或属性拦截),那么应该考虑在AspectJ里实现切面,利用Spring的DI把Spring Bean注入到AspectJ切面中。
经典的基于代理的AOP:
Spring支持五种类型的通知: Before(前) org.apringframework.aop.MethodBeforeAdvice After-returning(返回后) org.springframework.aop.AfterReturningAdvice After-throwing(抛出后) org.springframework.aop.ThrowsAdvice Arround(周围) org.aopaliance.intercept.MethodInterceptor Introduction(引入) org.springframework.aop.IntroductionInterceptor
实现步骤:
1.创建通知:实现这几个接口,把其中的方法实现了
2.定义切点和通知者:在Spring配制文件中配置这些信息
3.使用ProxyFactoryBean来生成代理。
业务代码(接口):
package com.invicme.apps.aop.proxy; /** * * @author lucl * * 数学计算接口类 * */ public interface ArithmeticCalculate { public int add (int i, int j); public int div (int i, int j) throws DivisorIsZeroException; public String validateNum (String level, int i); }
业务代码(实现类):
package com.invicme.apps.aop.proxy; import org.apache.log4j.Logger; /** * * @author lucl * * 数学计算实现类 * */ public class ArithmeticCalculateImpl implements ArithmeticCalculate { private static final Logger logger = Logger.getLogger(ArithmeticCalculateImpl.class); private int i = 0; private int j = 0; public ArithmeticCalculateImpl () { this(0, 0); } public ArithmeticCalculateImpl (int i, int j) { this.i = i; this.j = j; } @Override public int add(int i, int j) { logger.info("The method add was invoke with args [" + i + ", " + j + "]"); int sum = i + j; logger.info("The method add ends with result [" + sum + "]"); return sum; } @Override public int div(int i, int j) throws DivisorIsZeroException { logger.info("The method div was invoke with args [" + i + ", " + j + "]"); if (j == 0) { throw new DivisorIsZeroException("除数不可为0"); } int result = i / j; logger.info("The method div ends with result [" + result + "]"); return result; } @Override public String validateNum(String level, int i) { logger.info("The method validateNum was invoke with args [" + level + ", " + i + "]"); String result = this.getMsg(i); logger.info("The method validateNum ends with result [" + result + "]"); return result; } private String getMsg (int i) { if (i > 0) { return "正数"; } return "负数"; } }
希望切入的日志操作:
package com.invicme.apps.aop.proxy; import java.lang.reflect.Method; import java.util.Arrays; import org.apache.log4j.Logger; import org.springframework.aop.AfterReturningAdvice; import org.springframework.aop.MethodBeforeAdvice; /** * * @author lucl * */ public class LogAdapter implements MethodBeforeAdvice, AfterReturningAdvice { private static final Logger logger = Logger.getLogger(LogAdapter.class); /** * 目标对象的方法执行之前打印日志 */ @Override public void before(Method method, Object[] args, Object target) throws Throwable { logger.info(target.getClass().getName() + "@" + method.getName() + " with args " + Arrays.asList(args) + " invoke."); } /** * 目标对象的方法执行之后打印日志 */ @Override public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable { logger.info(target.getClass().getName() + "@" + method.getName() + " ends with result " + returnValue + " ."); } }
Spring配置文件:
<?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" 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"> <!-- 业务类 --> <bean id="calculate" class="com.invicme.apps.aop.proxy.ArithmeticCalculateImpl" /> <!-- 切入的日志类 --> <bean id="logAdapter" class="com.invicme.apps.aop.proxy.LogAdapter" /> <!-- 定义正则表达式切点 --> <bean id="loggerPointcut" class="org.springframework.aop.support.JdkRegexpMethodPointcut"> <!-- 单个方法 --> <!-- <property name="pattern" value=".*add"/> --> <property name="patterns"> <list> <value>.*add</value> <value>.*iv</value> <value>.validate*</value> </list> </property> </bean> <bean id="loggerAdapterAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor"> <property name="advice" ref="logAdapter"/> <property name="pointcut" ref="loggerPointcut"/> </bean> <bean id="proxyFactoryBean" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="calculate"/> <property name="interceptorNames" value="loggerAdapterAdvisor" /> <property name="proxyInterfaces" value="com.invicme.apps.aop.proxy.ArithmeticCalculate" /> </bean> </beans>
Junit单元测试类:
package com.test.apps.spring.aop; import org.junit.Test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import com.invicme.apps.aop.proxy.ArithmeticCalculate; import com.invicme.apps.aop.proxy.DivisorIsZeroException; /** * * @author lucl * */ public class TestSpringProxyFactoryBean { @Test public void testProxyFactoryBean() { ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring/spring-context-aop.xml"); ArithmeticCalculate calculate = context.getBean("proxyFactoryBean", ArithmeticCalculate.class); calculate.add(1, 2); System.out.println("----------------------------------------------------------------"); try { calculate.div(12, 3); } catch (DivisorIsZeroException e) { e.printStackTrace(); } } }
输出结果:
说明:
ProxyFactoryBean是一个代理,我们可以把它转换为proxyInterfaces中指定的实现该interface的代理对象。
通过代理模式可以获取到业务日志中希望输出的日志内容。
OK!这是我们想要的结果,但是上面这个过程貌似有点复杂,尤其是配置切点跟通知,Spring提供了一种自动代理的功能,能让切点跟通知自动进行匹配,修改配置文件如下:
<?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" 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"> <!-- 业务类 --> <bean id="calculate" class="com.invicme.apps.aop.proxy.ArithmeticCalculateImpl" /> <!-- 切入的日志类 --> <bean id="logAdapter" class="com.invicme.apps.aop.proxy.LogAdapter" /> <!-- 定义正则表达式切点 --> <bean id="loggerPointcut" class="org.springframework.aop.support.JdkRegexpMethodPointcut"> <!-- 单个方法 --> <!-- <property name="pattern" value=".*add"/> --> <property name="patterns"> <list> <value>.*add</value> <value>.*iv</value> <value>.validate*</value> </list> </property> </bean> <bean id="loggerAdapterAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor"> <property name="advice" ref="logAdapter"/> <property name="pointcut" ref="loggerPointcut"/> </bean> <bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <!-- <bean id="proxyFactoryBean" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="calculate"/> <property name="interceptorNames" value="loggerAdapterAdvisor" /> <property name="proxyInterfaces" value="com.invicme.apps.aop.proxy.ArithmeticCalculate" /> </bean> --> </beans>
执行程序:
package com.test.apps.spring.aop; import org.junit.Test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import com.invicme.apps.aop.proxy.ArithmeticCalculate; import com.invicme.apps.aop.proxy.DivisorIsZeroException; /** * * @author lucl * */ public class TestSpringProxyFactoryBean { @Test public void testProxyFactoryBean() { ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring/spring-context-aop.xml"); /*ArithmeticCalculate calculate = context.getBean("proxyFactoryBean", ArithmeticCalculate.class);*/ ArithmeticCalculate calculate = context.getBean("calculate", ArithmeticCalculate.class); calculate.add(1, 2); System.out.println("----------------------------------------------------------------"); try { calculate.div(12, 3); } catch (DivisorIsZeroException e) { e.printStackTrace(); } } }
说明:org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator能够为方法匹配的bean自动创建代理!
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