白话Spring源码（十一）：Spring AOP源码分析-创建代理对象

╰半橙微兮° 2022-02-20 16:16 236阅读 0赞

上篇博客：[白话Spring源码（十）：Spring AOP源码分析-筛选合适的通知器][Spring_Spring AOP_-]分析了 Spring 是如何为目标 bean 筛选合适的通知器的。现在通知器选好了，接下来就要通过代理的方式将通知器（Advisor）所持有的通知（Advice）织入到 bean 的某些方法前后。

织入到 bean的原理是动态代理。那我们先了解一下动态代理：

### 动态代理 ###

动态代理有两种实现方法：jdk动态代理，CGLIB 动态代理。

**1.基于 JDK 的动态代理**

下面我来演示一下 JDK 动态代理的使用方式，如下：

目标类定义：

public interface UserService {
    
        void save(User user);
    
        void update(User user);
    }
    
    public class UserServiceImpl implements UserService {
    
        @Override
        public void save(User user) {
            System.out.println("save user info");
        }
    
        @Override
        public void update(User user) {
            System.out.println("update user info");
        }
    }

代理创建者定义：

public interface ProxyCreator {
    
        Object getProxy();
    }
    
    public class JdkProxyCreator implements ProxyCreator, InvocationHandler {
    
        private Object target;
    
        public JdkProxyCreator(Object target) {
            assert target != null;
            Class<?>[] interfaces = target.getClass().getInterfaces();
            if (interfaces.length == 0) {
                throw new IllegalArgumentException("target class don`t implement any interface");
            }
            this.target = target;
        }
    
        @Override
        public Object getProxy() {
            Class<?> clazz = target.getClass();
            // 生成代理对象
            return Proxy.newProxyInstance(clazz.getClassLoader(), clazz.getInterfaces(), this);
        }
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    
            System.out.println(System.currentTimeMillis() + " - " + method.getName() + " method start");
            // 调用目标方法
            Object retVal = method.invoke(target, args);
            System.out.println(System.currentTimeMillis() + " - " + method.getName() + " method over");
    
            return retVal;
        }
    }

如上，invoke 方法中的代理逻辑主要用于记录目标方法的调用时间，和结束时间。下面写点测试代码简单验证一下，如下：

public class JdkProxyCreatorTest {
    
        @Test
        public void getProxy() throws Exception {
            ProxyCreator proxyCreator = new JdkProxyCreator(new UserServiceImpl());
            UserService userService = (UserService) proxyCreator.getProxy();
            
            System.out.println("proxy type = " + userService.getClass());
            System.out.println();
            userService.save(null);
            System.out.println();
            userService.update(null);
        }
    }

关于 JDK 动态代理，这里先说这么多。我们来看一下 CGLIB 动态代理。

**2.基于 CGLIB 的动态代理**

当我们要为未实现接口的类生成代理时，就无法使用 JDK 动态代理了。那么此类的目标对象生成代理时应该怎么办呢？当然是使用 CGLIB 了。在 CGLIB 中，代理逻辑是封装在 MethodInterceptor 实现类中的，代理对象则是通过 Enhancer 类的 create 方法进行创建。下面我来演示一下CGLIB 创建代理对象的过程，如下：

目标类：

public class Tank59 {
    
        void run() {
            System.out.println("极速前行中....");
        }
    
        void shoot() {
            System.out.println("轰...轰...轰...轰...");
        }
    }

CGLIB 代理创建者

public class CglibProxyCreator implements ProxyCreator {
    
        private Object target;
    
        private MethodInterceptor methodInterceptor;
    
        public CglibProxyCreator(Object target, MethodInterceptor methodInterceptor) {
            assert (target != null && methodInterceptor != null);
            this.target = target;
            this.methodInterceptor = methodInterceptor;
        }
    
        @Override
        public Object getProxy() {
            Enhancer enhancer = new Enhancer();
            // 设置代理类的父类
            enhancer.setSuperclass(target.getClass());
            // 设置代理逻辑
            enhancer.setCallback(methodInterceptor);
            // 创建代理对象
            return enhancer.create();
        }
    }

方法拦截器 - 坦克再制造：

public class TankRemanufacture implements MethodInterceptor {
    
        @Override
        public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
            if (method.getName().equals("run")) {
                System.out.println("正在重造59坦克...");
                System.out.println("重造成功，已获取 ✨59改 之 超音速飞行版✨");
                System.out.print("已起飞，正在突破音障。");
    
                methodProxy.invokeSuper(o, objects);
    
                System.out.println("已击落黑鸟 SR-71，正在返航...");
                return null;
            }
    
            return methodProxy.invokeSuper(o, objects);
        }
    }

好了，下面开始演示，测试代码如下：

public class CglibProxyCreatorTest {
    
        @Test
        public void getProxy() throws Exception {
            ProxyCreator proxyCreator = new CglibProxyCreator(new Tank59(), new TankRemanufacture());
            Tank59 tank59 = (Tank59) proxyCreator.getProxy();
            
            System.out.println("proxy class = " + tank59.getClass() + "\n");
            tank59.run();
            System.out.println();
            System.out.print("射击测试：");
            tank59.shoot();
        }
    }

好了，动态代理简单介绍到这里。那Spring AOP怎么选择哪种方式呢？

这里用到了工厂模式，我们来看一下源码：

**AopProxy：获取代理接口**

public interface AopProxy {
    	/**
    	 * Creates a new Proxy object for the given object, proxying
    	 * the given interface. Uses the thread context class loader.
    	 */
    	public abstract Object getProxy();
    	/**
    	 * Creates a new Proxy object for the given object, proxying
    	 * the given interface. Uses the given class loader.
    	 */
    	public abstract Object getProxy(ClassLoader cl);
    }

**AopProxy实现类：**有两个实现方式JDK动态代理和CGLIB代理，所以有两个实现类：

![20190414132956278.png][]

这两个实现类现在先不展开，后面详细介绍。

**AopProxyFactory：工厂接口**

public interface AopProxyFactory {
    	
    	/**
    	 * Return an AopProxy for the given AdvisedSupport object
    	 * @param advisedSupport AOP configuration
    	 * @return an AOP proxy
    	 * @throws AopConfigException if the configuration is invalid
    	 */
    	AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException;
    
    }

**DefaultAopProxyFactory：工厂实现类：**

public class DefaultAopProxyFactory implements AopProxyFactory {
    
    	/**
    	 * @see org.springframework.aop.framework.AopProxyFactory#createAopProxy(org.springframework.aop.framework.AdvisedSupport)
    	 */
    	public AopProxy createAopProxy(AdvisedSupport advisedSupport) throws AopConfigException {
    		boolean useCglib = advisedSupport.getOptimize() || advisedSupport.getProxyTargetClass() || advisedSupport.getProxiedInterfaces().length == 0;
    		if (useCglib) {
    			return CglibProxyFactory.createCglibProxy(advisedSupport);
    		}
    		else {
    			// Depends on whether we have expose proxy or frozen or static ts
    			return new JdkDynamicAopProxy(advisedSupport);
    		}
    	}
    	
    	/**
    	 * Inner class to just introduce a CGLIB dependency
    	 * when actually creating a CGLIB proxy.
    	 */
    	private static class CglibProxyFactory {
    
    		private static AopProxy createCglibProxy(AdvisedSupport advisedSupport) {
    			return new Cglib2AopProxy(advisedSupport);
    		}
    	}
    
    }

DefaultAopProxyFactory 根据一些条件决定生成什么类型的 AopProxy 实现类对象。

好了，关于创建代理的源码分析，就先说到这里吧。

[Spring_Spring AOP_-]: https://blog.csdn.net/haoxin963/article/details/89074883
[20190414132956278.png]: /images/20220220/2e4d57693ea649dcab71af546053e270.png