刚开始看到aop的时候,了解到它是面向切片,觉得还是挺拗口的。不知道应该怎么去理解怎么这么一个概念。后来想了一想,不如先看范例,直接从实例去理解aop或许更容易一点。
。从实例代码来看,aop更类似于用一种拦截器的方法去实现方法与方法直接调用的解耦。也就是说,方法之间的调用不再用硬编码的形式来实现,而是通过applicationContext.xml脚本配置的形式来完成。参考的实例内容略多,这里整理成一个完整的范例,大家可以逐步调试分析。
1、利用IDEA创建工程,选择“Spring”和“Application”
2、工程命名为Hello,创建完毕后,IDEA会自动下载好spring的jar库
3、创建CustomerService.java文件
public class CustomerService {
private String name;
private String url;
public void setName(String name) {
this.name = name;
}
public void setUrl(String url) {
this.url = url;
}
public void printName() {
System.out.println("Customer name : " + this.name);
}
public void printURL() {
System.out.println("Customer website : " + this.url);
}
public void printThrowException() {
throw new IllegalArgumentException();
}
}
4、编写Test测试类Test.java,这部分和之前差别不大
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main(String[] args) {
ApplicationContext appContext = new ClassPathXmlApplicationContext(
new String[] { "applicationContext.xml" });
CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");
System.out.println("*************************");
cust.printName();
System.out.println("*************************");
cust.printURL();
System.out.println("*************************");
try {
cust.printThrowException();
} catch (Exception e) {
}
}
}
5、准备各种各样的劫持类,比如事先劫持类、事后劫持类、异常劫持类、全部劫持类等
5.1 事前劫持类,继承自MethodBeforeAdvice
import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;
public class HijackBeforeMethod implements MethodBeforeAdvice
{
@Override
public void before(Method method, Object[] args, Object target)
throws Throwable {
System.out.println("HijackBeforeMethod : Before method hijacked!");
}
}
5.2 事后劫持类,继承自AfterReturningAdvice
import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;
public class HijackAfterMethod implements AfterReturningAdvice
{
@Override
public void afterReturning(Object returnValue, Method method,
Object[] args, Object target) throws Throwable {
System.out.println("HijackAfterMethod : After method hijacked!");
}
}
5.3 异常劫持,继承自ThrowsAdvice
import org.springframework.aop.ThrowsAdvice;
public class HijackThrowException implements ThrowsAdvice {
public void afterThrowing(IllegalArgumentException e) throws Throwable {
System.out.println("HijackThrowException : Throw exception hijacked!");
}
}
注意到,这里的劫持方法没有@Override声明。
5.4 全部劫持,继承自MethodInterceptor
import java.util.Arrays;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class HijackAroundMethod implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation methodInvocation) throws Throwable {
System.out.println("Method name : "
+ methodInvocation.getMethod().getName());
System.out.println("Method arguments : "
+ Arrays.toString(methodInvocation.getArguments()));
// same with MethodBeforeAdvice
System.out.println("HijackAroundMethod : Before method hijacked!");
try {
// proceed to original method call
Object result = methodInvocation.proceed();
// same with AfterReturningAdvice
System.out.println("HijackAroundMethod : After method hijacked!");
return result;
} catch (IllegalArgumentException e) {
// same with ThrowsAdvice
System.out.println("HijackAroundMethod : Throw exception hijacked!");
throw e;
}
}
}
这个劫持方法是功能最完整的劫持方法。此外,在invoke方法中,也需要自己调用methodInvocation.proceed来调用被劫持的函数。此外,对于异常,invoke方法也可以做到劫持访问。
6、准备和创建applicaitonContext.xml文件,方法参照上一篇blog内容
<?xml version="1.0" encoding="UTF-8"?>
<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.xsd">
<bean id="customerService" class="CustomerService">
<property name="name" value="baidu" />
<property name="url" value="www.baidu.com" />
</bean>
<bean id="hijackBeforeMethodBean" class="HijackBeforeMethod" />
<bean id="hijackAfterMethodBean" class="HijackAfterMethod" />
<bean id="hijackThrowExceptionBean" class="HijackThrowException" />
<bean id="hijackAroundMethodBean" class="HijackAroundMethod" />
<bean id="customerServiceProxy"
class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="target" ref="customerService" />
<property name="interceptorNames">
<list>
<value>hijackBeforeMethodBean</value>
<!--<value>hijackAfterMethodBean</value>
<value>hijackThrowExceptionBean</value>
<value>hijackAroundMethodBean</value>-->
</list>
</property>
</bean>
</beans>
7、调试Test.java文件,不妨选择hijackBeforeMethodBean做测试,右击选择“Run Test.main函数”,
不出意外,就可以看到这样的打印结果,