设计模式之代理模式

代理模式

1. 代理模式分为静态代理和动态代理．下图为静态代理结构图：

2. 静态代理示例代码：

   // 抽象主题接口
   public interface Subject {
   
       void request();
   }
   
   // 具体主题角色
   public class RealSubject implements Subject{
       @Override
       public void request() {
           System.out.println("真实对象处理请求．．．");
           Random random = new Random();
           try {
               Thread.sleep(random.nextInt(1000));
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
       }
   }
   
   // 代理角色
   public class Proxy implements Subject{
   
       private Subject subject;
   
       public Proxy(Subject subject) {
           this.subject = subject;
       }
   
       @Override
       public void request() {
           System.out.println("代理对象开始处理请求．．．");
           before();
           subject.request();
           after();
       }
   
       private void after() {
           System.out.println("proxy end...");
       }
   
       private void before() {
           System.out.println("proxy start...");
       }
   }
   // 测试
   public class ProxyTest {
   
       public static void main(String[] args) {
   
           Proxy proxy = new Proxy(new RealSubject());
           proxy.request();
       }
   }
   
   

3. JDK动态代理示例代码：

   // 抽象接口
   public interface Person {
   
       void findWork();
   }
   
   // 具体对象
   public class Worker implements Person{
       @Override
       public void findWork() {
           System.out.println("打工人要找工作．．．");
       }
   }
   
   // 代理类，实现的是InvocationHandler接口
   public class JdkHr implements InvocationHandler {
   
       private Person target;
   
       public Person getInstance(Person person){
           this.target = person;
           Class<? extends Person> targetClass = target.getClass();
           return (Person) Proxy.newProxyInstance(targetClass.getClassLoader(), targetClass.getInterfaces(), this);
       }
   
       @Override
       public Object invoke(Object o, Method method, Object[] objects) throws Throwable {
           before();
           Object invoke = method.invoke(this.target, objects);
           after();
           return invoke;
       }
   
       private void after() {
           System.out.println("proxy end...");
       }
   
       private void before() {
           System.out.println("proxy start...");
       }
   }
   
   // 测试
   public class JdkProxyTest {
   
       public static void main(String[] args) {
           // 这一行设置保存程序运行时的动态代理类class文件，方便查看
           System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true");
           JdkHr hr = new JdkHr();
           Person person = hr.getInstance(new Worker());
           person.findWork();
       }
   }
   
   

4. CGLib动态代理示例代码：

     ```java
     // 抽象接口
     public interface Person {
     
         void findWork();
     }
     
     // 具体对象
     public class Worker implements Person{
         @Override
         public void findWork() {
             System.out.println("打工人要找工作．．．");
         }
     }
     
     // 代理类，实现的是MethodInterceptor接口
     public class CglibHr implements MethodInterceptor {
     
         public Object getInstance(Class<?> clazz){
             Enhancer enhancer = new Enhancer();
             enhancer.setSuperclass(clazz);
             enhancer.setCallback(this);
             return enhancer.create();
         }
     
         @Override
         public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
             before();
             Object obj = methodProxy.invokeSuper(o, objects);
             after();
             return obj;
         }
     
         private void after() {
             System.out.println("proxy end...");
         }
     
         private void before() {
             System.out.println("proxy start...");
         }
     
     }
     
     // 测试
     public class CglibProxyTest {
     
         public static void main(String[] args) {
             // 这一行设置保存程序运行时的动态代理类class文件
             System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "cglibProxy/");
             CglibHr hr = new CglibHr();
             Person person = (Person) hr.getInstance(Worker.class);
             person.findWork();
         }
     }
     
     ```
   

5. JDK和CGLib动态代理对比：

6. 静态代理和动态代理对比：

7. 总结：

   代理模式优点：将代理对象与真实被调用目标对象分离，降低了系统耦合性，扩展性好，并且可以增强目标对象的功能；

   代理模式缺点：系统中类的数量增加，导致处理请求的速度变慢，增加了系统的复杂度．