JDK及CGLIB动态代理-AOP4种增强-优快云博客

本文深入探讨了AOP(面向切面编程)的概念及其实现方式，包括JDK动态代理与CGLIB两种底层技术原理，并通过示例代码详细解释了如何在Java中运用这两种技术实现动态代理。此外，还介绍了四种不同的增强类型：前置增强、后置增强、环绕增强及异常增强。

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动态代理 AOP底层实现：有接口自动应用的就是JDK动态代理
（1）.JDK 在运行时运行时注入
本质：在内存中构建出接口的实现类
特点：被代理对象，必须有接口

实例：

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class Test {
    public static void main(String[] args) {
      final SomeService service = new SomeServiceImpl();

      SomeService proxy =(SomeService)Proxy.newProxyInstance(service.getClass().getClassLoader(),
              service.getClass().getInterfaces(), new InvocationHandler() {
                  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                      System.out.println("before=======");
                      method.invoke(service,args);
                      System.out.println("after========");
                      return null;
                  }
              });
      proxy.doSome();
    }
}

Cglib 底层，注入，编译期已经注入了
本质：在内存中生成被代理类（目标类）的【子类】
特点：可以在没有接口的情况下代理
对于不使用接口的业务类，无法使用JDK动态代理，cglib采用非常底层的字节码技术，
可以为一个类创建子类

import cn.SomeServiceImpl;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;


public class Test {
    public static void main(String[] args) {
        final SomeServiceImpl someService = new SomeServiceImpl();

        Enhancer enhancer = new Enhancer();

        enhancer.setSuperclass(someService.getClass());
        enhancer.setCallback(new MethodInterceptor() {
            public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
                System.out.println("=======before");
                methodProxy.invoke(someService,objects);
                return null;
            }
        });
        SomeServiceImpl proxy = (SomeServiceImpl) enhancer.create();
        proxy.doSome();
    }
}

接下来是四种增强

前置增强 MethodBeforeAdvice

import org.springframework.aop.AfterReturningAdvice;

import java.lang.reflect.Method;

public class AfterAdvice implements AfterReturningAdvice {
    public void afterReturning(Object o, Method method, Object[] objects, Object o1) throws Throwable {
        System.out.println("after========");
    }
}

<bean id="service" class="cn.SomeServiceImpl"></bean>

    <bean id="beforeAdvice" class="cn.BeforeAdvice"></bean>

    <bean id="proxyService" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="service"></property>
        <property name="interceptorNames" value="beforeAdvice"></property>
    </bean>

后置增强 AfterReturingAdvice

import org.springframework.aop.AfterReturningAdvice;

import java.lang.reflect.Method;

public class AfterAdvice implements AfterReturningAdvice {
    public void afterReturning(Object o, Method method, Object[] objects, Object o1) throws Throwable {
        System.out.println("after========");
    }
}

xml文件内容

   <bean id="service" class="cn.SomeServiceImpl"></bean>

    <bean id="afterAdvice" class="cn.AfterAdvice"></bean>

    <bean id="proxyService" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="service"></property>
        <property name="interceptorNames" value="afterAdvice"></property>
    </bean>

3.环绕增强

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class HrAdvice implements MethodInterceptor {
    public Object invoke(MethodInvocation methodInvocation) throws Throwable {
        System.out.println("before====");
        methodInvocation.proceed();
        System.out.println("after====");
        return null;
    }
}

xml文件

   <bean id="service" class="cn.SomeServiceImpl"></bean>

    <bean id="hrAdvice" class="cn.HrAdvice"></bean>

    <bean id="proxyService" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="service"></property>
        <property name="interceptorNames" value="hrAdvice"></property>
    </bean>

异常增强

public class MyThrowsAdvice implements ThrowsAdvice {
    public void afterThrowing(Exception e){
        System.out.println("网络异常......");
    }
}

   <bean id="service" class="cn.SomeServiceImpl"></bean>

    <bean id="throwsAdvice" class="cn.MyThrowsAdvice"></bean>

    <bean id="proxyService" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="service"></property>
        <property name="interceptorNames" value="throwsAdvice"></property>
    </bean>

转载于:https://www.cnblogs.com/buai/p/8587800.html