2021-05-29_传统纵向继承体系-优快云博客

AOP

1). AOP: AOP Aspect Oriented Programing 面向切面编程
2).AOP采取横向抽取机制，取代了传统纵向继承体系重复性代码
3). Spring AOP使用纯Java实现，不需要专门的编译过程和类加载器，在运行
期通过代理方式向目标类织入增强代

正常使用类：*.java -> javac -> .class -> java -> 加载该class到虚拟机
动态代理直接生成了.class字节码, 加载该class到虚拟机

AOP的好处

为什么说 AOP采取横向抽取机制，取代了传统纵向继承体系重复性代码呢？
在这里插入图片描述

为什么spring要采用aop横向抽取机制？
因为传统的纵向继承方式，是采用继承的方式来利用这些重复的代码。这样做会增加类与类的耦合性，程序会显得特别笨重，而且后期也难以维护。
而aop采用的横向抽取机制则避免了这一问题。

AOP底层原理;

AOP的这种横向抽取机制就是采用了代理机制。
spring默认使用jdk动态代理，如果没有实现接口，就使用cglib代理
1）JDK动态代理：只能针对接口实现代理， jdk动态代理在高版本中性能优于CGLib

//目标类和代理类实现的 接口
public interface UserDao {

public void insert();

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">delete</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">select</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

}

//目标类
public class UserDaoTarget implements UserDao {
    public void insert() {
        System.out.println("插入方法");
    }
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">delete</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"删除方法"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"更新方法"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">select</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"查询方法"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

//代理类
public class ProxyUserDao {
   private UserDao userDao;
<span class="token keyword">public</span> <span class="token function">ProxyUserDao</span><span class="token punctuation">(</span>UserDao userDao<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>userDao <span class="token operator">=</span> userDao<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> UserDao <span class="token function">createProxy</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    <span class="token comment">//获得类加载器</span>
    ClassLoader classLoader <span class="token operator">=</span> userDao<span class="token punctuation">.</span><span class="token function">getClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getClassLoader</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">//代理对象需要实现的接口</span>
    Class<span class="token operator">&lt;</span><span class="token operator">?</span><span class="token operator">&gt;</span><span class="token punctuation">[</span><span class="token punctuation">]</span> interfaces <span class="token operator">=</span> userDao<span class="token punctuation">.</span><span class="token function">getClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getInterfaces</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">//通知类</span>
    UserDaoAdvice userDaoAdvice <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">UserDaoAdvice</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    UserDao proxy <span class="token operator">=</span> <span class="token punctuation">(</span>UserDao<span class="token punctuation">)</span> Proxy<span class="token punctuation">.</span><span class="token function">newProxyInstance</span><span class="token punctuation">(</span>classLoader<span class="token punctuation">,</span>interfaces<span class="token punctuation">,</span>userDaoAdvice<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> proxy<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

//通知类
public class UserDaoAdvice implements InvocationHandler {
    UserDao userDao = new UserDaoTarget();
<span class="token comment">//调用目标对象中的任意方法都相当于调用该invoke方法。</span>
<span class="token keyword">public</span> Object <span class="token function">invoke</span><span class="token punctuation">(</span>Object proxy<span class="token punctuation">,</span> Method method<span class="token punctuation">,</span> Object<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> Throwable <span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"方法被执行，记录日志信息"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    Object obj <span class="token operator">=</span> method<span class="token punctuation">.</span><span class="token function">invoke</span><span class="token punctuation">(</span>userDao<span class="token punctuation">,</span>args<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">return</span> obj<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

//测试类
public class ProxyTest {
<span class="token annotation punctuation">@Test</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">test</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>

    UserDao userdao <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">UserDaoTarget</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">//获得代理对象</span>
    UserDao proxy <span class="token operator">=</span>  <span class="token keyword">new</span> <span class="token class-name">ProxyUserDao</span><span class="token punctuation">(</span>userdao<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">createProxy</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">//代理对象调用方法</span>
    proxy<span class="token punctuation">.</span><span class="token function">delete</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

2）.CGLib动态代理：既可以针对接口实现代理，也可以生成子类充当目标父类的代理

//目标类
public class ProductDao {
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">select</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"查询商品"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">insert</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"插入商品"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">update</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"更新商品"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">delete</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"删除商品"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

//代理类
public class CGLibProxy {
   private ProductDao productDao;
    public CGLibProxy(ProductDao productDao) {
        this.productDao = productDao;
    }
    public ProductDao createproxy(){
        //创建核心类
        Enhancer enhancer = new Enhancer();
        //为其设置父类
        enhancer.setSuperclass(productDao.getClass());
        //设置回调
        enhancer.setCallback(new ProductDaoAdvice());
    <span class="token comment">//创建代理</span>

    <span class="token keyword">return</span> <span class="token punctuation">(</span>ProductDao<span class="token punctuation">)</span> enhancer<span class="token punctuation">.</span><span class="token function">create</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

//通知类
public class ProductDaoAdvice implements MethodInterceptor {
    ProductDao productDao = new ProductDao();
    /*
         方法参数说明：Object o 目标对象
                      Method method  方法对象
                      Object[] objects 方法中的参数
                      MethodProxy methodProxy
     */
    public Object intercept(Object proxy, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"执行了方法，记录了日志信息"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    Object o1 <span class="token operator">=</span> method<span class="token punctuation">.</span><span class="token function">invoke</span><span class="token punctuation">(</span>productDao<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token comment">// CGLib特有的方式 ：Object o = methodProxy.invokeSuper(proxy);</span>
    <span class="token keyword">return</span> o1<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

测试类
public class CGLibTest {
    ProductDao productDao = new ProductDao();
    @Test
    public void test2(){
        ProductDao createproxy = new CGLibProxy(productDao).createproxy();
        createproxy.delete();
    }
}
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