Spring系列(四):Spring AOP详解

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 Before advice(前置通知):在目标方法被调用之前调用通知;

    ② After returning advice(返回通知):在目标方法成功执行之后调用通知;

    ③ After throwing advice(异常通知):在目标方法抛出异常后调用通知;

    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 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?

  我们定义一个接口类:UserService

package com.toby.service;

/**
 * @desc: user 业务接口类
 * @author: toby
 * @date: 2019/8/4 23:28
 */
public interface UserService {
    /**
     * 添加
     */
    void add();
    
    /**
     * say hello
     * @param name
     * @return
     */
    String say(String name);
}

  在定义一个实现类UserServiceImpl

package com.toby.service.impl;

import com.toby.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @desc: user业务的实现类
 * @author: toby
 * @date: 2019/8/4 23:29
 */
@Service
public class UserServiceImpl implements UserService {

    @Override
    public void add() {
        System.out.println("执行UserServiceImpl的add方法");
    }

    @Override
    public String say(String name) {
        System.out.println("执行UserServiceImpl的say方法 args = " + name);
        return "hello " + name;
    }
}

  第一种:静态代理

  定义一个静态代理类,需要实现UserService接口:

package com.toby.proxy;

import com.toby.service.UserService;

/**
 * @desc: 静态代理
 * @author: toby
 * @date: 2019/8/4 23:30
 */
public class StaticProxy implements UserService {

    private UserService userService;

    public StaticProxy(UserService userService){
        this.userService = userService;
    }

    @Override
    public void add() {
        System.out.println("添加日志开始");
        userService.add();
        System.out.println("添加日志结束");
    }

    @Override
    public String say(String name) {
        return "";
    }
}

  第二种: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;
    }
}

  第三种: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.toby.proxy.generator;

import com.toby.service.impl.UserServiceImpl;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import sun.misc.ProxyGenerator;

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

/**
 * @desc: 字节码生成器
 * @author: toby
 * @date: 2019/8/5 0:05
 */
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();
    }
}

  第四种: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() { \n" +
                "System.out.println(\"Javassist字节码日志记录开始\");\n" +
                "targetObject.add();\n" +
                "System.out.println(\"Javassist字节码日志记录结束\");\n"+
                "}", 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

<aop:aspectj-autoproxy/>

  声明一个Aspect

@Aspect
@Component
public class UserAspect {
}

  声明一个Pointcut

@Pointcut("execution(* com.toby.service.UserService.*(..))")//the pointcut expression
public void pointCutExecution(){}//the pointcut signature

  Spring AOP支持的9种切入点表达式

  ① execution:execution用于匹配方法执行 join points连接点,最小粒度方法 

execution(modifiers-pattern? ret-type-pattern declaring-type-pattern?name-pattern(param-pattern) throws-pattern?)
这里问号表示当前项可以有也可以没有,其中各项的语义如下
modifiers-pattern:方法的可见性,如public,protected;
ret-type-pattern:方法的返回值类型,如int,void等;
declaring-type-pattern:方法所在类的全路径名,如com.spring.Aspect;
name-pattern:方法名类型,如buisinessService();
param-pattern:方法的参数类型,如java.lang.String;
throws-pattern:方法抛出的异常类型,如java.lang.Exception;
example:
@Pointcut("execution(* com.toby.dao.*.*(..))")//匹配com.toby.dao包下的任意接口和类的任意方法
@Pointcut("execution(public * com.toby.dao.*.*(..))")//匹配com.toby.dao包下的任意接口和类的public方法
@Pointcut("execution(public * com.toby.dao.*.*())")//匹配com.toby.dao包下的任意接口和类的public 无方法参数的方法
@Pointcut("execution(* com.toby.dao.*.*(java.lang.String, ..))")//匹配com.toby.dao包下的任意接口和类的第一个参数为String类型的方法
@Pointcut("execution(* com.toby.dao.*.*(java.lang.String))")//匹配com.toby.dao包下的任意接口和类的只有一个参数,且参数为String类型的方法
@Pointcut("execution(* com.toby.dao.*.*(java.lang.String))")//匹配com.toby.dao包下的任意接口和类的只有一个参数,且参数为String类型的方法
@Pointcut("execution(public * *(..))")//匹配任意的public方法
@Pointcut("execution(* te*(..))")//匹配任意的以te开头的方法
@Pointcut("execution(* com.toby.dao.IndexDao.*(..))")//匹配com.toby.dao.IndexDao接口中任意的方法
@Pointcut("execution(* com.toby.dao..*.*(..))")//匹配com.toby.dao包及其子包中任意的方法
关于这个表达式的详细写法,可以参考官网:https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/core.html#aop-pointcuts-examples

  定义一个AopConfig配置类:

package com.toby.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.EnableAspectJAutoProxy;

/**
 * @desc: aop配置类
 * @author: toby
 * @date: 2019/8/5 23:48
 */
@Configuration
/**
 * 此处需要注意的是,如果配置设置proxyTargetClass=false,或默认为false,则是用JDK代理,否则使用的是CGLIB代理
 * 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。
 * 所以使用target会保证目标不变,匹配目标对象不会受到这个设置的影响。
 * 但是使用this时,会根据该选项的设置,CGLIB this可以代理原因是继承了被代理的对象也就是目标对象,JDK的this就不能被代理了。
 */
@EnableAspectJAutoProxy(proxyTargetClass = true)
@ComponentScan(basePackages="com.toby")
public class AopConfig {
}

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * For matching method execution join points. This is the primary pointcut designator to use when working with Spring AOP.
     * execution用于匹配方法执行 join points连接点,最小粒度方法
     * 详细用法参考:https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/core.html#aop-pointcuts-examples
     */
    @Pointcut("execution(* com.toby.service.UserService.*(..))")
    public void pointCutExecution(){}

    @Before("pointCutExecution()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutExecution()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  定义一个启动测试类AopMain(下同):

package com.toby;

import com.toby.config.AopConfig;
import com.toby.service.UserService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @desc: aop启动类
 * @author: toby
 * @date: 2019/8/5 23:50
 */
public class AopMain {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AopConfig.class);
        UserService userService = context.getBean(UserService.class);
        userService.say("toby");
    }
}

  运行结果如下:

《Spring系列(四):Spring AOP详解》

  ② within:用于匹配指定类型内的方法执行, within与execution相比,粒度更大,仅能实现到包和接口、类级别。而execution可以精确到方法的返回值,参数个数、修饰符、参数类型等。

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points within certain types (the execution of a method declared within a matching type when using Spring AOP).
     * 用于匹配指定类型内的方法执行, within与execution相比,粒度更大,仅能实现到包和接口、类级别。而execution可以精确到方法的返回值,参数个数、修饰符、参数类型等
     */
    @Pointcut("within(com.toby.service.impl.UserServiceImpl)")
    public void pointCutWithin(){}

    @Before("pointCutWithin()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutWithin()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  运行结果如下:

《Spring系列(四):Spring AOP详解》

  ③ this:用于匹配当前AOP代理对象类型的执行方法;注意是AOP代理对象的类型匹配 

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points (the execution of methods when using Spring AOP) where the bean reference (Spring AOP proxy) is an instance of the given type.
     * 用于匹配当前AOP代理对象类型的执行方法;注意是AOP代理对象的类型匹配
     */
    @Pointcut("this(com.toby.service.impl.UserServiceImpl)")
    public void pointCutThis(){}

    @Before("pointCutThis()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutThis()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  @EnableAspectJAutoProxy(proxyTargetClass = true),则用CGLIB代理,而CGLIB继承被代理的类来实现,所以this能匹配到,运行结果:

《Spring系列(四):Spring AOP详解》

   @EnableAspectJAutoProxy,默认proxyTargetClass = false,如果基于接口则用JDK代理,所以this匹配不到,运行结果:

《Spring系列(四):Spring AOP详解》

  ④ target:用于匹配当前目标对象类型的执行方法

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points (the execution of methods when using Spring AOP) where the target object (application object being proxied) is an instance of the given type.
     * 用于匹配当前目标对象类型的执行方法
     */
    @Pointcut("target(com.toby.service.impl.UserServiceImpl)")
    public void pointCutTarget(){}

    @Before("pointCutTarget()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutTarget()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  运行结果如下:

《Spring系列(四):Spring AOP详解》

  ⑤ args:用于匹配当前执行的方法传入的参数为指定类型的执行方法

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points (the execution of methods when using Spring AOP) where the arguments are instances of the given types.
     * 用于匹配当前执行的方法传入的参数为指定类型的执行方法
     */
    @Pointcut("args(java.lang.String)")
    public void pointCutArgs(){}

    @Before("pointCutArgs()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutArgs()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  定义一个启动测试类AopMain:

package com.toby;

import com.toby.config.AopConfig;
import com.toby.service.UserService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @desc: aop启动类
 * @author: toby
 * @date: 2019/8/5 23:50
 */
public class AopMain {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AopConfig.class);
        UserService userService = context.getBean(UserService.class);
        //不能被增强
        userService.add();
        //能被增强 匹配到了参数String类型
        userService.say("toby");
    }
}

  运行结果如下:

《Spring系列(四):Spring AOP详解》

  ⑥ @target:匹配目标对象类型是否有指定的注解

  定义目标对象UserServiceImpl如下:

package com.toby.service.impl;

import com.toby.anno.Toby;
import com.toby.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @desc: user业务的实现类
 * @author: toby
 * @date: 2019/8/4 23:29
 */
@Service
@Toby
public class UserServiceImpl implements UserService {

    @Override
    public void add() {
        System.out.println("执行UserServiceImpl的add方法");
    }

    @Override
    public String say(String name) {
        System.out.println("执行UserServiceImpl的say方法 args = " + name);
        return "hello " + name;
    }
}

  定义一个注解Log:

package com.toby.anno;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * @desc: 日志注解
 * @author: toby
 * @date: 2019/8/5 23:06
 */
@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Log {
}

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points (the execution of methods when using Spring AOP) where the class of the executing object has an annotation of the given type.
     * 用于匹配目标对象类型是否有指定的注解
     */
    @Pointcut("@target(com.toby.anno.Log)")
    public void pointCutTargetAnno(){}

    @Before("pointCutTargetAnno()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutTargetAnno()")
    public void after(){
        System.out.println("--------after--------");
    }
}

  运行结果如下:

《Spring系列(四):Spring AOP详解》

  ⑦ @args:匹配方法参数所属的类型上有指定的注解(例子略)

  ⑧ @within:用于匹配所持有指定注解类型内的所以连接点也就是方法(例子略)

  ⑨ @annotation:用于匹配当前执行方法持有指定注解的方法(注解作用在方法上面)

  定义目标对象UserServiceImpl如下:

package com.toby.service.impl;

import com.toby.anno.Log;
import com.toby.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @desc: user业务的实现类
 * @author: toby
 * @date: 2019/8/4 23:29
 */
@Service
public class UserServiceImpl implements UserService {

    @Override
    public void add() {
        System.out.println("执行UserServiceImpl的add方法");
    }

    @Override
    @Log
    public String say(String name) {
        System.out.println("执行UserServiceImpl的say方法 args = " + name);
        return "hello " + name;
    }
}

  定义一个UserAspect:

package com.toby.aspect;

import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @desc: 用户切面,该切面一定要交给spring容器管理
 * @author: toby
 * @date: 2019/8/5 22:56
 */
@Aspect
@Component
public class UserAspect {

    /**
     * Limits matching to join points where the subject of the join point (the method being executed in Spring AOP) has the given annotation.
     * 用于匹配当前执行方法持有指定注解的方法(注解作用在方法上面);
     */
    @Pointcut("@annotation(com.toby.anno.Log)")
    public void pointCutAnno(){}

    @Before("pointCutAnno()")
    public void before(){
        System.out.println("--------before--------");
    }

    @After("pointCutAnno()")
    public void after(){
        System.out.println("--------after--------");
    }
}

   运行结果发现:userService.add();//不能被增强 userService.say(“toby”);//能被增强,因为say方法上有@Log注解;

   总结:本章讲解了Spring AOP的核心概念和应用场景,Spring AOP可以帮我们解决编程过程中的一些横切性问题,比如我们要记录日志,事务管理,性能监控,权限认证等。使的这些问题能和我们业务逻辑分开,达到了解耦的目的,代码的重用性更高。如何声明一个Aspect,声明一个Pointcut以及Spring AOP支持的9种切入点表达式。Spring AOP的代理方式有2种,一个是JDK一个CGLIB,如果配置设置proxyTargetClass=false,或默认为false,则是用JDK代理,否则使用的是CGLIB代理,注意JDK动态代理必须实现接口,否则还是会走CGLIB动态代理。(后续的源码解析会分析到原因),Spring系列完整代码在码云:spring系列

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