spring中的动态代理

不念不忘少年蓝@ 2022-04-24 01:50 355阅读 0赞

# 一.背景介绍 #

之前介绍了动态代理的两种方式  
jdk动态代理:[https://blog.csdn.net/qq\_24516549/article/details/89085881][https_blog.csdn.net_qq_24516549_article_details_89085881]  
cglib动态代理:[https://blog.csdn.net/qq\_24516549/article/details/89167591][https_blog.csdn.net_qq_24516549_article_details_89167591]

现在开始研究在spring中的实现有什么不同

# 二.示例代码 #

##### 1.注解 #####

import java.lang.annotation.Documented;
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target({  ElementType.METHOD,ElementType.TYPE })
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface MyTest { 
    
    }

##### 2.切面类 #####

import java.lang.reflect.Method;
    
    import org.aspectj.lang.JoinPoint;
    import org.aspectj.lang.annotation.Aspect;
    import org.aspectj.lang.annotation.Before;
    import org.aspectj.lang.annotation.Pointcut;
    import org.aspectj.lang.reflect.MethodSignature;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.context.annotation.Configuration;
    
    @Aspect
    @Configuration
    public class MyTestAspect { 
    
    	Logger log = LoggerFactory.getLogger(MyTestAspect.class);
    
    	@Pointcut("@annotation(cn.test.modules.aop.aoptest.annotation.MyTest)")
    	public void pointCut() { 
    	}
    
    	@Before("pointCut()")
    	public void doBefore(JoinPoint point) throws ClassNotFoundException, NoSuchMethodException, SecurityException { 
    		log.info("before:" + getMethod(point).getName());
    	}
    
    	private Method getMethod(JoinPoint point) throws NoSuchMethodException, SecurityException { 
    		MethodSignature methodSignature = (MethodSignature) point.getSignature();
    		Class<?> targetClass = point.getTarget().getClass();
    		return targetClass.getMethod(methodSignature.getName(), methodSignature.getParameterTypes());
    	}
    }

##### 3.service #####

import org.springframework.stereotype.Service;
    
    import cn.test.modules.aop.aoptest.annotation.MyTest;
    
    @Service
    public class AService { 
    
    	@MyTest
    	public void test() { 
    	}
    
    	@MyTest
    	public void hello() { 
    		test();
    	}
    
    }

##### 4.controller #####

import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    import cn.test.modules.aop.aoptest.classService.AService;
    import io.swagger.annotations.ApiOperation;
    import cn.test.common.utils.R;
    
    /** * * * @author zhanchong * @email zhanchong316@foxmail.com * @date 2019-04-10 14:24:36 */
    @RestController
    @RequestMapping("aop/test")
    public class TestController { 
    	@Autowired
    	private AService a;
    
    	/** * 列表 */
    	@RequestMapping("/test")
    	@ApiOperation(value = "测试aop", httpMethod = "GET")
    	public R list(int type) { 
    		switch (type) { 
    		case 1:
    			a.hello();
    			break;
    		case 2:
    			a.test();
    			break;
    		case 3:
    			AService A = new AService();
    			A.hello();
    			break;
    		default:
    			break;
    		}
    		return R.ok();
    	}
    
    }

# 三.代码调用示例 #

以上注解和切面类期望达到调用注上MyTest注解的方法之前打印一行log,依次调用123三种情况查看结果

## 1.demo1 ##

##### 1 #####

输出:

2019-04-11 15:18:52.660  INFO 13244 --- [io-8080-exec-25] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:hello

只输出了hello()方法上的日志,可见自调用的test()方法未被增强

##### 2 #####

输出:

2019-04-11 15:20:10.338  INFO 13244 --- [io-8080-exec-24] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:test

正常输出了test()方法上的日志

##### 3 #####

无输出,未发生任何增强

## 2.demo2 ##

修改service代码如下:

import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.aop.framework.AopContext;
    import org.springframework.aop.support.AopUtils;
    import org.springframework.context.annotation.EnableAspectJAutoProxy;
    import org.springframework.stereotype.Service;
    
    import cn.test.modules.aop.aoptest.annotation.MyTest;
    
    @Service
    @EnableAspectJAutoProxy(exposeProxy = true)
    public class AService { 
    
    	Logger log = LoggerFactory.getLogger(AService.class);
    
    	@MyTest
    	public void test() { 
    		Object o = AopContext.currentProxy();
    		log.info("test start");
    		log.info(AopUtils.isAopProxy(o) + "");
    		log.info(AopUtils.isJdkDynamicProxy(o) + "");
    		log.info(AopUtils.isCglibProxy(o) + "");
    		log.info("test end");
    	}
    
    	@MyTest
    	public void hello() { 
    		Object o = AopContext.currentProxy();
    		log.info("hello start");
    		log.info(AopUtils.isAopProxy(o) + "");
    		log.info(AopUtils.isJdkDynamicProxy(o) + "");
    		log.info(AopUtils.isCglibProxy(o) + "");
    		log.info("hello end");
    		test();
    	}
    
    }

依次调用123三种情况查看结果

##### 1 #####

输出:

2019-04-11 15:26:46.620  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:hello
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : hello start
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : false
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : hello end
    2019-04-11 15:26:46.622  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : test start
    2019-04-11 15:26:46.624  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:26:46.624  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : false
    2019-04-11 15:26:46.624  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:26:46.624  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : test end

可见hello被增强,test未被增强;  
当前调用的对象是被spring管理的动态代理对象,动态代理方式是cglib

##### 2 #####

输出:

2019-04-11 15:20:10.338  INFO 13244 --- [io-8080-exec-24] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:test2019-04-11 15:27:06.379  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:test
    2019-04-11 15:27:06.380  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.classService.AService  : test start
    2019-04-11 15:27:06.380  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:27:06.380  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.classService.AService  : false
    2019-04-11 15:27:06.380  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.classService.AService  : true
    2019-04-11 15:27:06.380  INFO 13244 --- [nio-8080-exec-6] c.t.m.aop.aoptest.classService.AService  : test end

可见test被增强  
当前调用的对象是被spring管理的动态代理对象,动态代理方式是cglib

##### 3 #####

2019-04-11 15:27:33.504 ERROR 13244 --- [nio-8080-exec-7] c.t.common.exception.RRExceptionHandler  : Cannot find current proxy: Set 'exposeProxy' property on Advised to 'true' to make it available.

报错,调用自定义对象并非被spring管理的对象

## 3.demo3 ##

修改service代码如下:

import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.aop.framework.AopContext;
    import org.springframework.context.annotation.EnableAspectJAutoProxy;
    import org.springframework.stereotype.Service;
    
    import cn.test.modules.aop.aoptest.annotation.MyTest;
    
    @Service
    @EnableAspectJAutoProxy(exposeProxy = true)
    public class AService { 
    
    	Logger log = LoggerFactory.getLogger(AService.class);
    
    	@MyTest
    	public void test() { 
    		log.info("test start");
    		log.info(AopContext.currentProxy().getClass().getName());
    		log.info("test end");
    	}
    
    	@MyTest
    	public void hello() { 
    		log.info("hello start");
    		log.info(AopContext.currentProxy().getClass().getName());
    		log.info("hello end");
    		((AService) AopContext.currentProxy()).test();
    	}
    
    }

查看1的结果

##### 1 #####

输出:

2019-04-11 15:33:31.397  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:hello
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : hello start
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : cn.test.modules.aop.aoptest.classService.AService$$EnhancerBySpringCGLIB$$2641a8af
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : hello end
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:test
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : test start
    2019-04-11 15:33:31.400  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : cn.test.modules.aop.aoptest.classService.AService$$EnhancerBySpringCGLIB$$2641a8af
    2019-04-11 15:33:31.401  INFO 13244 --- [nio-8080-exec-1] c.t.m.aop.aoptest.classService.AService  : test end

可见hello和test均被增强;  
当前调用的对象属于`cn.test.modules.aop.aoptest.classService.AService$$EnhancerBySpringCGLIB$$2641a8af`类

## 4.demo4 ##

修改service代码如下:

@MyTest
    	public void test() { 
    		log.info("test start");
    		log.info("test end");
    	}
    
    	@MyTest
    	public void hello() { 
    		log.info("hello start");
    		log.info(AopContext.currentProxy().getClass().getName());
    		log.info("hello end");
    		new AService().test();
    	}

查看1的结果

##### 1 #####

输出:

2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.aspect.MyTestAspect    : before:hello
    2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : hello start
    2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : cn.test.modules.aop.aoptest.classService.AService$$EnhancerBySpringCGLIB$$2641a8af
    2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : hello end
    2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : test start
    2019-04-11 15:37:08.917  INFO 13244 --- [nio-8080-exec-3] c.t.m.aop.aoptest.classService.AService  : test end

可见hello被增强,test未被增强;  
当前调用的对象属于`cn.test.modules.aop.aoptest.classService.AService$$EnhancerBySpringCGLIB$$2641a8af`类

# 四.代码调用分析 #

由上可见,spring在这里采用cglib来管理被动态代理的对象,那么我们之前有看到cglib生成的代理类自调用是会被增强的,为什么spring的cglib代理对象自调用增强不起作用呢?  
这是因为spring实现的cglib是cglib风格的代理,实际上还是用类似jdk动态代理中委托的形式来实现的…

关于此我看到如下解释:  
**The behavior of the Cglib-proxies has nothing to do with the way of how cglib works but with how cglib is used by Spring. Cglib is capable of either delegating or subclassing a call. Have a look at Spring’s DynamicAdvisedInterceptor which implements this delegation. Using the MethodProxy, it could instead perform a super method call.  
Spring defines delegation rather than subclassing in order to minimize the difference between using Cglib or Java proxies.**  
根据以上内容及分析,我们应该可以看出来,spring容器中ioc管理的对象默认是原生对象,但只要该类通过aop增强,该对象就是代理对象,我们用代理对象来调用方法才会触发各种代理增强

关于spring如何选择代理方式,之前可能有看到过优先使用jdk动态代理,没有接口再使用cglib动态代理;  
实际上现在任何情况下都会优先选择cglib动态代理,选择jdk动态代理必须手动指定才行了

# 五.spring的ioc和di #

从上面的示例中我们可以看到,直接用autowired注入的对象是被aop增强的我们期望得到的对象,而自己new出来的则只是原始对象

如果我们想要获得被代理的对象,不通过spring的话,需要手动调用代理控制类去增强原始对象,AOP在spring里用的不要太多,可想而知会有多麻烦

而spring就改变了这一情况,他把控制反转了,之前是程序主动去创建依赖对象,而spring则是有一个容器来创建这些对象;所谓控制反转就是ioc容器控制了对这些对象的依赖获取

那么为什么叫反转呢,之前的情况是我们自己在程序中直接获取依赖的对象,这是正转;而现在是容器来创建和注入依赖对象,那么需要依赖对象的实例对依赖对象的依赖也就被反转了

下面参考开涛大神的讲解:

假设A类中有个方法的调用需要B类中的某个方法,而B类又依赖C类  
我们此时需要调用A类中的方法,之前需要先创建B对象,再创建C对象;再把C对象注入到B对象里,再调用B的方法  
现在,使用spring,我们只需在A类中注入B对象,关于B的依赖Spring会自动帮我们管理,这就是spring的依赖注入

所以说spring实现了依赖注入和控制反转,也实现了aop;

如果你不用依赖注入,那么也就不能方便的使用spring中的aop,而是需要很麻烦的手动设置原始对象的动态代理

下面参考bromon大神的讲解,讲的非常清晰明了:  
[https://blog.csdn.net/bromon/article/details/326250\#comments][https_blog.csdn.net_bromon_article_details_326250_comments]

Spring所倡导的开发方式就是如此，所有的类都会在spring容器中登记，告诉spring你是个什么东西，你需要什么东西，然后spring会在系统运行到适当的时候，把你要的东西主动给你，同时也把你交给其他需要你的东西。所有的类的创建、销毁都由 spring来控制，也就是说控制对象生存周期的不再是引用它的对象，而是spring。对于某个具体的对象而言，以前是它控制其他对象，现在是所有对象都被spring控制，所以这叫控制反转。

[https_blog.csdn.net_qq_24516549_article_details_89085881]: https://blog.csdn.net/qq_24516549/article/details/89085881
[https_blog.csdn.net_qq_24516549_article_details_89167591]: https://blog.csdn.net/qq_24516549/article/details/89167591
[https_blog.csdn.net_bromon_article_details_326250_comments]: https://blog.csdn.net/bromon/article/details/326250#comments