我們先來介紹下什麼是代理。
(學習影片分享:java影片教學)
代理程式是一種設計模式,它的核心思想,是將對目標的存取轉移到代理物件上。這樣做的好處就是,目標物件在不改變程式碼的情況下,可以透過代理物件加上一些額外的功能。這是一種程式設計思想,在不改變原有程式碼的情況下,透過代理程式增加一些擴充功能。
代理程式如圖所示,使用者存取代理對象,代理對象透過存取目標對象,來達到使用者存取目標對象的目的,
public interface IBlogService { void writeBlog(); }
public class BlogService implements IBlogService { @Override public void writeBlog() { System.out.println("i'm writing..."); } }
public class BlogStaticProxy implements IBlogService{ private IBlogService blogService; public BlogStaticProxy(IBlogService blogService) { this.blogService = blogService; } @Override public void writeBlog() { System.out.println("start writing..."); blogService.writeBlog(); System.out.println("end writing..."); } }
public class BlogStaticProxy implements IBlogService{ private IBlogService blogService; public BlogStaticProxy(IBlogService blogService) { this.blogService = blogService; } @Override public void writeBlog() { System.out.println("start writing..."); blogService.writeBlog(); System.out.println("end writing..."); } }
public class TestStaticProxy { public static void main(String[] args) { IBlogService target = new BlogService(); BlogStaticProxy proxy = new BlogStaticProxy(target); proxy.write(); } }
start writing… i’m writing… end writing…
public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException { }
public class JdkBlogProxyFactory { private Object target; public JdkBlogProxyFactory(Object target) { this.target = target; } public Object newInstance() { return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), (proxy, method, args) -> { System.out.println("start writing"); Object o = method.invoke(target, args); System.out.println("end writing"); return o; }); } }
public class TestJdkProxy { public static void main(String[] args) { IBlogService target = new BlogService(); System.out.println(target.getClass()); // 给目标对象,创建代理对象 IBlogService proxy = (IBlogService) new JdkBlogProxyFactory(target).newInstance(); // class $Proxy0 内存中动态生成的代理对象 System.out.println(proxy.getClass()); // 执行方法 【代理对象】 proxy.writeBlog(); } }
class com.forezp.proxy.BlogService class com.sun.proxy.$Proxy0 start writing i'm writing... end writing
public class CglibBlogFactory implements MethodInterceptor { private Object target; public CglibBlogFactory(Object target) { this.target = target; } //给目标对象创建一个代理对象 public Object getProxyInstance() { //1.工具类 Enhancer en = new Enhancer(); //2.设置父类 en.setSuperclass(target.getClass()); //3.设置回调函数 en.setCallback(this); //4.创建子类(代理对象) return en.create(); } @Override public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable { System.out.println("start writing..."); //执行目标对象的方法 Object returnValue = method.invoke(target, objects); System.out.println("end writing..."); return returnValue; } }
public class TestCglib { public static void main(String[] args) { IBlogService target = new BlogService(); //代理对象 IBlogService proxy = (IBlogService) new CglibBlogFactory(target).getProxyInstance(); //执行代理对象的方法 proxy.writeBlog(); } }
start writing... i'm writing... end writing...
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