Spring AOP总结(三)

一、AOP是什么
AOP（面向切面编程），可以说是一种编程思想，其中的Spring AOP和AspectJ都是现实了这种编程思想。相对OOP（面向过程编程）来说，提供了另外一种编程方式，对于OOP过程中产生的横切性问题，这些横切性与业务无关，可以通过预编译方式和运行期动态代理来实现。比如可以应用在：日志记录、性能监控、事务管理等。
二、AOP的基本概念

• Aspect（切面）：通常来说是一个类，里面定义了切点和通知，Spring AOP中可以用@AspectJ来标注这个类是切面；
• Join point（连接点）：可以理解成目标对象中的方法，该方法是要被增强的方法，也就是我们要作用的一个切入点；
• Pointcut（切点）：切点可以理解成连接点的集合；
• Target object（目标对象）：被代理的对象，也就是目标对象；
• AOP proxy（代理对象）：把被代理的对象织入了增强后的对象；
• Weaving（织入）：把增强也就是代理逻辑加入到目标对象上的过程；
• Advice（通知）：用于指定在特定连接点上的增强的位置；

1. ① Before advice（前置通知）：在目标方法被调用之前调用通知；
2. ② After returning advice（返回通知）：在目标方法成功执行之后调用通知；
3. ③ After throwing advice（异常通知）：在目标方法抛出异常后调用通知；
4. ④ After (finally) advice（后置通知）：在目标方法完成之后调用通知（不论是否出现异常都会执行，finally中调用）；
5. ⑤ Around advice（环绕通知）：围绕连接点(目标方法)的通知。可以在方法调用前后执行自定义行为；

三、代理的实现方式
我们知道AOP可以通过预编译的方式和运行期动态代理来实现，那么代理的实现方式有哪些呢？第一种：Jdk动态代理

package com.toby.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

/**
 * @desc: JDK动态代理 实现一个接口：InvocationHandler
 * JDK的动态代理机制只能代理实现了接口的类，而没有实现接口的类就不能实现JDK的动态代理
 * @author: toby
 * @date: 2019/8/4 23:34
 */
public class JdkDynamicProxy implements InvocationHandler {
    /**
     * 目标对象
     */
    private Object targetObject;

    public Object createJdkProxy(final Object targetObject){
        this.targetObject = targetObject;
        return Proxy.newProxyInstance(this.targetObject.getClass().getClassLoader(),
                this.targetObject.getClass().getInterfaces(),this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //写对应的增强代码
        System.out.println("Jdk日志记录开始");
        //调用真正的业务方法
        Object obj = method.invoke(this.targetObject,args);
        System.out.println("Jdk日志记录结束");
        return obj;
    }
}

第二种：Cglib动态代理

package com.toby.proxy;

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

import java.lang.reflect.Method;

/**
 * @desc: CGLIB动态代理 cglib是针对类来实现代理的，他的原理是对指定的目标类生成一个子类，
 * 并覆盖其中方法实现增强，但因为采用的是继承，所以不能对final修饰的类进行代理
 * @author: toby
 * @date: 2019/8/4 23:43
 */
public class CglibDynamicProxy implements MethodInterceptor {

    /**
     * 目标对象
     */
    private Object targetObject;

    /**
     * 创建Cglib动态代理
     * @param targetObject
     * @return
     */
    public Object createCglibDynamicProxy(final Object targetObject){
        this.targetObject = targetObject;
        //Cglib中的核心对象，该类用于生成代理对象
        Enhancer enhancer = new Enhancer();
        //指定委托类也就是目标对象为父类
        enhancer.setSuperclass(this.targetObject.getClass());
        //使用代理，需要一个对应的代理对象
        enhancer.setCallback(this);
        return enhancer.create();
    }

    @Override
    public Object intercept(Object o, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        System.out.println("CGLIB日志记录开始");
        //委托类变成了父类。调用真正的服务提供者
        Object obj = methodProxy.invoke(this.targetObject,args);
        System.out.println("CGLIB日志记录结束");
        return obj;
    }
}

JDK代理的实现方式是基于接口实现，代理类继承Proxy，实现接口。而CGLIB继承被代理的类来实现；这就是为什么JDK动态代理需要实现接口的原因？Java是单继承
下面定义一个字节码生成器ByteCodeGenerator来一看究竟：

package com.springboot.study.tests.aop;

import net.sf.cglib.proxy.Enhancer;
import org.aopalliance.intercept.MethodInterceptor;
import sun.misc.ProxyGenerator;

import java.io.File;
import java.io.FileOutputStream;
import java.lang.reflect.Modifier;
import java.nio.file.Files;

/**
 * @Author: guodong
 * @Date: 2021/10/10 15:16
 * @Version: 1.0
 * @Description:
 */
public class ByteCodeGenerator{

    /**
     * 根据目标对象生成字节码(Jdk)
     * @param target
     * @param <T>
     * @return
     */
    public static <T> byte[] generatorByteCodeByJdkProxy(T target){
        int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
        byte [] codes = ProxyGenerator.generateProxyClass("Proxy$"+target.getClass().getName(), target.getClass().getInterfaces(),accessFlags);
        return codes;
    }

    /**
     * 根据目标对象生成字节码(Cglib)
     * @param target
     * @param <T>
     * @return
     * @throws Exception
     */
    public static <T> byte[] generatorByteCodeByCglib(final T target) throws Exception {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(target.getClass());
        enhancer.setCallback((MethodInterceptor) (o, method, objects, methodProxy) -> methodProxy.invoke(target,objects));
        enhancer.create();
        byte [] codes = enhancer.getStrategy().generate(enhancer);
        return codes;
    }

    public static void main(String[] args) {
        /**
         * 测试jdk
         */
        try {
            byte [] codes = ByteCodeGenerator.generatorByteCodeByJdkProxy(new UserServiceImpl());
            File file = new File(System.getProperty("user.dir")+"/spring-aop/target/Proxy$UserServiceImpl.class");
            Files.write(file.toPath(),codes);
        } catch (Exception e) {
            e.printStackTrace();
        }
        
        /**
         * 测试cglib
         */
        try {
            FileOutputStream out = new FileOutputStream(System.getProperty("user.dir")+"/spring-aop/target/Cglib$UserServiceImpl.class");
            out.write(ByteCodeGenerator.generatorByteCodeByCglib(new UserServiceImpl()));
            out.flush();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

Jdk生成的动态代理字节码：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package Proxy$com.toby.service.impl;

import com.toby.service.UserService;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class UserServiceImpl extends Proxy implements UserService {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public UserServiceImpl(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final void add() throws  {
        try {
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("com.toby.service.UserService").getMethod("add");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

Cglib生成动态代理的字节码：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.toby.service.impl;

import java.lang.reflect.Method;
import org.springframework.cglib.core.ReflectUtils;
import org.springframework.cglib.core.Signature;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

public class UserServiceImpl$$EnhancerByCGLIB$$b26297df extends UserServiceImpl implements Factory {
    private boolean CGLIB$BOUND;
    public static Object CGLIB$FACTORY_DATA;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private static Object CGLIB$CALLBACK_FILTER;
    private static final Method CGLIB$add$0$Method;
    private static final MethodProxy CGLIB$add$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$equals$1$Method;
    private static final MethodProxy CGLIB$equals$1$Proxy;
    private static final Method CGLIB$toString$2$Method;
    private static final MethodProxy CGLIB$toString$2$Proxy;
    private static final Method CGLIB$hashCode$3$Method;
    private static final MethodProxy CGLIB$hashCode$3$Proxy;
    private static final Method CGLIB$clone$4$Method;
    private static final MethodProxy CGLIB$clone$4$Proxy;

    static void CGLIB$STATICHOOK2() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("com.toby.service.impl.UserServiceImpl$$EnhancerByCGLIB$$b26297df");
        Class var1;
        Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
        CGLIB$equals$1$Method = var10000[0];
        CGLIB$equals$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$1");
        CGLIB$toString$2$Method = var10000[1];
        CGLIB$toString$2$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$2");
        CGLIB$hashCode$3$Method = var10000[2];
        CGLIB$hashCode$3$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$3");
        CGLIB$clone$4$Method = var10000[3];
        CGLIB$clone$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$4");
        CGLIB$add$0$Method = ReflectUtils.findMethods(new String[]{"add", "()V"}, (var1 = Class.forName("com.toby.service.impl.UserServiceImpl")).getDeclaredMethods())[0];
        CGLIB$add$0$Proxy = MethodProxy.create(var1, var0, "()V", "add", "CGLIB$add$0");
    }

    final void CGLIB$add$0() {
        super.add();
    }

    public final void add() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$add$0$Method, CGLIB$emptyArgs, CGLIB$add$0$Proxy);
        } else {
            super.add();
        }
    }

    final boolean CGLIB$equals$1(Object var1) {
        return super.equals(var1);
    }

    public final boolean equals(Object var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var2 = var10000.intercept(this, CGLIB$equals$1$Method, new Object[]{var1}, CGLIB$equals$1$Proxy);
            return var2 == null ? false : (Boolean)var2;
        } else {
            return super.equals(var1);
        }
    }

    final String CGLIB$toString$2() {
        return super.toString();
    }

    public final String toString() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy) : super.toString();
    }

    final int CGLIB$hashCode$3() {
        return super.hashCode();
    }

    public final int hashCode() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var1 = var10000.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
            return var1 == null ? 0 : ((Number)var1).intValue();
        } else {
            return super.hashCode();
        }
    }

    final Object CGLIB$clone$4() throws CloneNotSupportedException {
        return super.clone();
    }

    protected final Object clone() throws CloneNotSupportedException {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? var10000.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy) : super.clone();
    }

    public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -1422568652:
            if (var10000.equals("add()V")) {
                return CGLIB$add$0$Proxy;
            }
            break;
        case -508378822:
            if (var10000.equals("clone()Ljava/lang/Object;")) {
                return CGLIB$clone$4$Proxy;
            }
            break;
        case 1826985398:
            if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                return CGLIB$equals$1$Proxy;
            }
            break;
        case 1913648695:
            if (var10000.equals("toString()Ljava/lang/String;")) {
                return CGLIB$toString$2$Proxy;
            }
            break;
        case 1984935277:
            if (var10000.equals("hashCode()I")) {
                return CGLIB$hashCode$3$Proxy;
            }
        }

        return null;
    }

    public UserServiceImpl$$EnhancerByCGLIB$$b26297df() {
        CGLIB$BIND_CALLBACKS(this);
    }

    public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
        CGLIB$THREAD_CALLBACKS.set(var0);
    }

    public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
        CGLIB$STATIC_CALLBACKS = var0;
    }

    private static final void CGLIB$BIND_CALLBACKS(Object var0) {
        UserServiceImpl$$EnhancerByCGLIB$$b26297df var1 = (UserServiceImpl$$EnhancerByCGLIB$$b26297df)var0;
        if (!var1.CGLIB$BOUND) {
            var1.CGLIB$BOUND = true;
            Object var10000 = CGLIB$THREAD_CALLBACKS.get();
            if (var10000 == null) {
                var10000 = CGLIB$STATIC_CALLBACKS;
                if (var10000 == null) {
                    return;
                }
            }

            var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
        }

    }

    public Object newInstance(Callback[] var1) {
        CGLIB$SET_THREAD_CALLBACKS(var1);
        UserServiceImpl$$EnhancerByCGLIB$$b26297df var10000 = new UserServiceImpl$$EnhancerByCGLIB$$b26297df();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        UserServiceImpl$$EnhancerByCGLIB$$b26297df var10000 = new UserServiceImpl$$EnhancerByCGLIB$$b26297df();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        UserServiceImpl$$EnhancerByCGLIB$$b26297df var10000 = new UserServiceImpl$$EnhancerByCGLIB$$b26297df;
        switch(var1.length) {
        case 0:
            var10000.<init>();
            CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
            return var10000;
        default:
            throw new IllegalArgumentException("Constructor not found");
        }
    }

    public Callback getCallback(int var1) {
        CGLIB$BIND_CALLBACKS(this);
        MethodInterceptor var10000;
        switch(var1) {
        case 0:
            var10000 = this.CGLIB$CALLBACK_0;
            break;
        default:
            var10000 = null;
        }

        return var10000;
    }

    public void setCallback(int var1, Callback var2) {
        switch(var1) {
        case 0:
            this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
        default:
        }
    }

    public Callback[] getCallbacks() {
        CGLIB$BIND_CALLBACKS(this);
        return new Callback[]{this.CGLIB$CALLBACK_0};
    }

    public void setCallbacks(Callback[] var1) {
        this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
    }

    static {
        CGLIB$STATICHOOK2();
    }
}

第三种：Javassist动态代理（在动态字节码插桩详解）
① 定义一个JavassistDynamicProxy实现Javassist动态代理：

package com.toby.proxy;

import javassist.util.proxy.ProxyFactory;
import javassist.util.proxy.ProxyObject;

/**
 * @desc: javassist
 * @author: toby
 * @date: 2019/8/15 20:22
 */
public class JavassistDynamicProxy {

    /**
     * 创建Javassist动态代理
     * @param targetObject
     * @throws Exception
     * @return
     */
    public Object createJavassistDynamicProxy(final Object targetObject)throws Exception {
        ProxyFactory factory = new ProxyFactory();
        factory.setInterfaces(targetObject.getClass().getInterfaces());
        Class<?> proxyClass = factory.createClass();
        Object javassistProxy = proxyClass.newInstance();
        ((ProxyObject)javassistProxy).setHandler((self,thisMethod,proceed,args)-> {
            //写对应的增强代码
            System.out.println("Javassist日志记录开始");
            //调用真正的业务方法
            Object obj = thisMethod.invoke(targetObject,args);
            System.out.println("Javassist日志记录结束");
            return obj;
        });
        return javassistProxy;
    }
}

② 定义一个JavassistBytecodeDynamicProxy实现Javassist动态代理：

package com.toby.proxy;

import javassist.*;

import java.lang.reflect.Field;

/**
 * @desc: javassist 字节码动态代理
 * @author: toby
 * @date: 2019/8/15 20:42
 */
public class JavassistBytecodeDynamicProxy {

    /**
     * 创建Javassist字节码动态代理
     * @param targetObject
     * @return
     * @throws Exception
     */
    public static Object createJavassistBytecodeDynamicProxy(final Object targetObject) throws Exception {
        ClassPool pool = ClassPool.getDefault();
        CtClass proxyClass = pool.makeClass("JavassistProxy" +  "&" +targetObject.getClass().getName());
        proxyClass.addInterface(pool.get(targetObject.getClass().getInterfaces()[0].getName()));
        proxyClass.addConstructor(CtNewConstructor.defaultConstructor(proxyClass));
        proxyClass.addField(CtField.make("private " + targetObject.getClass().getName() + " targetObject;", proxyClass));
        proxyClass.addMethod(CtNewMethod.make("public void add() { 
" +
                "System.out.println("Javassist字节码日志记录开始");
" +
                "targetObject.add();
" +
                "System.out.println("Javassist字节码日志记录结束");
"+
                "}", proxyClass));
        Class<?> clazz = proxyClass.toClass();
        Object bytecodeProxy = clazz.newInstance();
        Field field = bytecodeProxy.getClass().getDeclaredField("targetObject");
        field.setAccessible(true);
        field.set(bytecodeProxy,targetObject);
        return bytecodeProxy;
    }

    /**
     * 创建Javassist字节码动态代理2
     * @param targetObject
     * @return
     * @throws Exception
     */
    public static Object createJavassistBytecodeDynamicProxy2(final Object targetObject) throws Exception {
        ClassPool pool = ClassPool.getDefault();
        pool.appendSystemPath();
        CtClass ctl = pool.get(targetObject.getClass().getName());
        ctl.setName("JavassistProxy" +  "&" + targetObject.getClass().getName());
        CtMethod ctMethod = ctl.getDeclaredMethod("add");
        ctMethod.insertBefore("System.out.println("Javassist字节码2日志记录开始");");
        ctMethod.insertAfter("System.out.println("Javassist字节码2日志记录结束");");
        Class<?> clazz = ctl.toClass();
        Object bytecodeProxy = clazz.newInstance();
        return bytecodeProxy;
    }
}

四、Spring AOP
Spring AOP提供两种编程风格，详细用法见Spring官网：https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/core.html#aop-aspectj-support
① @AspectJ support（利用aspectj的注解）
② Schema-based AOP support（基于xml aop:config命名空间）
启用@AspectJ支持
① 使用Java Configuration启用@AspectJ支持：要使用Java @Configuration启用@AspectJ支持，要添加@EnableAspectJAutoProxy注释：

@Configuration
@EnableAspectJAutoProxy
public class AppConfig {

}

② 使用XML配置启用@AspectJ支持：要使用基于xml的配置启用@AspectJ支持，可以使用aop:aspectj-autoproxy元素

参考博客：https://www.cnblogs.com/toby-xu/p/11361351.html