动态代理

对目标对象进行增强，增强动作与目标动作分开、解耦

cglib性能较高但是费时，实用于 无需频繁创建代理对象或有实例池的代理 

 

例子

写arrayList动态代理类

final List list = new ArrayList();
List proxyInstance =
        (List) Proxy.newProxyInstance(list.getClass().getClassLoader(),
                list.getClass().getInterfaces(),
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        return method.invoke(list, args);
                    }
                });
    proxyInstance.add("你好");
    System.out.println(list);

http://www.bjpowernode.com/tutorial_baseinterviewquestions/239.html

这是什么代理？

 http://www.bjpowernode.com/tutorial_baseinterviewquestions/239.html

 

JDK：基于反射、反射基于接口

精髓：拦截器InvocationHandler

代码我就不重新写一套了，实例代码这块还是比较简单的

借用大佬的分享把我的重点分享一下

 public interface PersonService {
	
	public String savePerson();
	
	public void deletePerson();
	
}
实现类
public class PersonServiceImpl implements PersonService{
 
	@Override
	public String savePerson() {
		System.out.println("添加");
		return "保存成功！";
	}
 
	@Override
	public void deletePerson() {
		System.out.println("删除");
	}
 
}

 

增强类：可以没有，去掉相关的代码即可，主要是增强的动作不一定是类的形式

public class MyTransaction {
	public void beginTransaction(){
		System.out.println("开启事务，或其他的业务 ");
	}
	public void commit(){
		System.out.println("提交事务");
	}
}

 

自定义拦截器：可添加自己的业务 

public class PersonServiceInterceptor implements InvocationHandler{
	//目标类，要执行的方法
	private Object target;
	//增强类，额外的处理
	private MyTransaction myTransaction;
	//构造函数注入目标类和增强类
	public PersonServiceInterceptor(Object target,MyTransaction myTransaction){
		this.target = target;
		this.myTransaction = myTransaction;
	}
 
	//代理类的每一个方法被调用的时候都会调用下边的这个invoke方法
	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		this.myTransaction.beginTransaction();
		Object returnValue = method.invoke(this.target, args);
		this.myTransaction.commit();
		return returnValue;
	}
	
}

测试

public class ProxyTest {
	@Test
	public void test(){
		Object target = new PersonServiceImpl();
		MyTransaction myTransaction = new MyTransaction();
		PersonServiceInterceptor interceptor = new PersonServiceInterceptor(target, myTransaction);
              //关键，增强类可以没有，去掉相关的代码即可；拦截器一定要有
		PersonService personService = (PersonService)Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(),interceptor);
		String returnValue = (String)personService.savePerson();
		System.out.println(returnValue);
	}
}

 

https://www.cnblogs.com/lxcmyf/p/6433018.html

https://blog.csdn.net/ju_362204801/article/details/90714295

 

cglib：字节码技术，代理类创建子类来代理

代理对象为目标对象子类

代理的类和增强类是一样的

实现拦截器不同：

public class PersonServiceInterceptor implements MethodInterceptor{
	
	private Object target;
	
	private MyTransaction myTransaction;
	
	public PersonServiceInterceptor(Object target,MyTransaction myTransaction){
		this.target = target;
		this.myTransaction = myTransaction;
	}
	//利用增强器创建代理，
	public Object createProxy(){
		Enhancer enhancer = new Enhancer();
		enhancer.setCallback(this);
		enhancer.setSuperclass(this.target.getClass());
		return enhancer.create();
	}
 
	@Override
	public Object intercept(Object object, Method method, Object[] args,MethodProxy methodProxy) throws Throwable {
		myTransaction.beginTransaction();
		Object returnValue = method.invoke(this.target, args);
		myTransaction.commit();
		return returnValue;
	}
	
}

测试：
public class ProxyTest {
	@Test
	public void test(){
		Object target = new PersonServiceImpl();
		MyTransaction myTransaction = new MyTransaction();
		PersonServiceInterceptor interceptor = new PersonServiceInterceptor(target, myTransaction);
		PersonService personService =(PersonService) interceptor.createProxy();
		String returnValue = (String)personService.savePerson();
		System.out.println(returnValue);
	}
}

也可以把增强器拿出来：

public class Landlord {
    public void rent(){
        System.out.println("房东要出租房子了！");
    }
}

public class Intermediary implements MethodInterceptor {

    @Override
    public Object intercept(Object object, Method method, Object[] args,MethodProxy methodProxy) throws Throwable {
        Object intercept = methodProxy.invokeSuper(object, args);
        System.out.println("中介：该房源已发布！");
        return intercept;
    }
}

public class Test {
    public static void main(String[] args) {
        Intermediary intermediary = new Intermediary();
        
        Enhancer enhancer = new Enhancer();  
        enhancer.setSuperclass(Landlord.class);
        enhancer.setCallback(intermediary);
        
        Landlord rentProxy = (Landlord) enhancer.create();
        rentProxy.rent();
    }
}

 

说到代理不得不提AOP，原因你懂的

springaop 代理类 增强类不需要自己实现，配置文件配置或使用注解，spring会帮你生成代理对象，上面的两种代理spring据情况不同对应生成代理对象

可喜的是aop简单易懂

 

https://blog.csdn.net/qq_39470733/article/details/77315010?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase

 

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https://baijiahao.baidu.com/s?id=1628782377871648532&wfr=spider&for=pc