使用AspectJ LTW(Load Time Weaving)【转载】

来源：互联网发布：市政工程预算软件编辑：程序博客网时间：2024/06/03 08:16

原文地址：http://log-cd.iteye.com/blog/562056

在Java 语言中，从织入切面的方式上来看，存在三种织入方式：编译期织入、类加载期织入和运行期织入。编译期织入是指在Java编译期，采用特殊的编译器，将切面织入到Java类中；而类加载期织入则指通过特殊的类加载器，在类字节码加载到JVM时，织入切面；运行期织入则是采用CGLib工具或JDK动态代理进行切面的织入。
    AspectJ采用编译期织入和类加载期织入的方式织入切面，是语言级的AOP实现，提供了完备的AOP支持。它用AspectJ语言定义切面，在编译期或类加载期将切面织入到Java类中。
    AspectJ提供了两种切面织入方式，第一种通过特殊编译器，在编译期，将AspectJ语言编写的切面类织入到Java类中，可以通过一个Ant或Maven任务来完成这个操作；第二种方式是类加载期织入，也简称为LTW（Load Time Weaving）。
    使用AspectJ LTW有两个主要步骤，第一，通过JVM的-javaagent参数设置LTW的织入器类包，以代理JVM默认的类加载器；第二，LTW织入器需要一个 aop.xml文件，在该文件中指定切面类和需要进行切面织入的目标类。

    设置-javaagent JVM参数的方法:
(1)在Eclipse下的设置:
运行类->右键单击->Run As->Run...，可以在弹出的Run设置窗口设置该类的各项运行属性，切换到Arguments Tab页，在VM arguments中通过-javaagent指定AspectJ 织入器类包。-javaagent:E:\workspace\lib\spring2.5\aspectjweaver.jar
(2)在Tomcat下的设置
打开<Tomcat_Home>\bin\catalina.bat，在该批处理文件头部添加以下的设置：
set JAVA_OPTS=-javaagent:E:\workspace\lib\spring2.5\aspectjweaver.jar

一、配置LTW织入器的aop.xml配置文件
    LTW织入器在工作时，首先会查找类路径下META-INF /aop.xml的配置文件，并根据配置文件的设置进行织入的操作。

Xml代码

<?xml version="1.0" encoding="UTF-8"?>
<aspectj>
<aspects>
<aspect name="quickstart.aspectj.Monitor" />
</aspects>
<weaver
options="-showWeaveInfo -XmessageHandlerClass:org.springframework.aop.aspectj.AspectJWeaverMessageHandler">
<include within="quickstart.service..*" />
</weaver>
</aspectj>

二、切面织入的目标类和切面实例

Java代码

package quickstart.service.impl;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
import quickstart.dao.PersonDao;
import quickstart.model.Person;
import quickstart.service.PeopleService;
public class PeopleServiceImpl implements PeopleService{
//通过类型(byType为默认)的自动连接可能会有多个候选,
//通过使用@Qualifier注解，使用名称(byName)来限定
@Autowired
@Qualifier("personDao")
private PersonDao personDao;
@Transactional(propagation = Propagation.REQUIRED)
public void savePerson(Person person) {
personDao.save(person);
}
@Transactional(readOnly = true, propagation = Propagation.REQUIRED)
public Person findPersonById(Integer id) {
return personDao.findById(id);
}
@Transactional(readOnly = true, propagation = Propagation.REQUIRED)
public List findPersonByJPQL(String jpql){
return personDao.findByJPQL(jpql);
}

Java代码

package quickstart.aspectj;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
@Aspect
public class Monitor {
@Pointcut("execution(* quickstart.service.impl.*.*(..))")
public void anyService(){}
@Before("quickstart.aspectj.Monitor.anyService()")
public void log(JoinPoint joinPoint){
System.out.println("Service Method " + joinPoint.getSignature().getName() + " Invocation!");
}
}

三、Spring配置文件applicationContext.xml

Xml代码

<?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"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd">
<bean id="momitor" class="quickstart.aspectj.Monitor" factory-method="aspectOf"/>
<bean
class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>
<bean
class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />
<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="jpaVendorAdapter">
<bean
class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="database" value="MYSQL" />
<property name="showSql" value="true" />
</bean>
</property>
</bean>
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost/test?useUnicode=true&characterEncoding=UTF-8" />
<property name="username" value="root" />
<property name="password" value="root" />
</bean>
<bean id="transactionManager"
class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<tx:annotation-driven transaction-manager="transactionManager" />
<bean id="jpaTemplate" class="org.springframework.orm.jpa.JpaTemplate">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
<bean id="personDao" class="quickstart.dao.impl.PersonDaoImpl" autowire="byName"/>
<bean id="peopleService" class="quickstart.service.impl.PeopleServiceImpl"/>
</beans>

四、测试

Java代码

package logcd.test;
import java.util.List;
import org.junit.BeforeClass;
import org.junit.Ignore;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import quickstart.model.Address;
import quickstart.model.Person;
import quickstart.service.PeopleService;
public class JpaServiceTest {
private static ApplicationContext appContext;
private static PeopleService peopleService;
@BeforeClass
public static void Init(){
appContext = new ClassPathXmlApplicationContext("applicationContext.xml");
peopleService = (PeopleService)appContext.getBean("peopleService");
}
@Test
public void findById(){
Person person = peopleService.findPersonById(new Integer(2));
System.out.println(person.getFirstName()+person.getLastName());
//System.out.println(person.getAddress().getStreetName());
}
@Test
public void findByJPQL(){
StringBuilder jpql = new StringBuilder();
jpql.append(" FROM Person p JOIN FETCH p.address");
List list = peopleService.findPersonByJPQL(jpql.toString());
for(Object obj : list){
Person person = (Person)obj;
System.out.println(person.getFirstName() + person.getLastName());
System.out.println(person.getAddress().getStreetName());
}
}
}

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