[9] Agency model [Better understanding of AOP]

10. Agency mode

Why learn the agency model?

Because this is the bottom layer of SpringAOP, [server-side development SpringAOP and SpringMVC interview must ask]

Classification of agent mode:

• Static proxy
• Dynamic proxy

10.1 Static proxy

Role analysis:

• Abstract role: generally use interfaces or abstract classes to solve
• Real role: the role of the agent
• Acting role: Acting for the real role, after acting for the real role, we usually do some subsidiary operations
• Client: The person who visits the proxy object!

step:

1. interface

   public interface Rent {
         
         
   
       public void rent();
   }
   

2. Real character (landlord)

   public class Host implements Rent{
         
         
       public void rent() {
         
         
           System.out.println("房东有房子出租");
       }
   }
   

3. Agent role

   public class Proxy implements Rent{
         
         
   
       private Host host;
   
       public Proxy() {
         
         
   
       }
   
       public Proxy(Host host) {
         
         
           this.host = host;
       }
   
       public void rent() {
         
         
           host.rent();
           viewHouse();
           contract();
           fee();
       }
   
       public void viewHouse(){
         
         
           System.out.println("中介带租客去看房子");
       }
   
       public void contract(){
         
         
           System.out.println("中介负责打印合同签合同");
       }
   
       public void fee(){
         
         
           System.out.println("收取中介费");
       }
   }
   

4. Customer access agent role

   public class Client {
         
         
   
       public static void main(String[] args) {
         
         
           Host host = new Host();
   
           Proxy proxy = new Proxy(host);
           proxy.rent();
       }
   }
   

Benefits of the agency model:

• Can make the operation of real characters more pure! No need to pay attention to some public business
• Public business is left to the agent role! Realize the division of labor
• When public business expands, it is convenient for centralized management.

Disadvantages:

• A real role will produce an agent role; the amount of code will double and the development efficiency will be lower

10.2 Deepen understanding

Talk about AOP:

10.3, dynamic proxy

• Dynamic agents have the same role as static agents

• The proxy class of dynamic proxy is dynamically generated, not written directly by us.

• Dynamic agents are divided into two categories: interface-based dynamic agents and class-based dynamic agents

  • Based on interface: JDK dynamic proxy
  • Based on class: cglib
  • Java bytecode implementation: javasist

• public interface InvocationHandler

  InvocationHandlerIt is an interface implemented by the call handler of the proxy instance .

  Each agent instance has an associated call handler. When a method is called on a proxy instance, the method call will be coded and dispatched to the invokemethod of its call handler .

• ProxyProvides static methods for creating dynamic proxy classes and instances. It is also the superclass of all dynamic proxy classes created by these methods.

Agency case:

1. Interface

package com.kuber.dynamicdemo1;

public interface UserService {
    
    
    public void add();
    public void delete();
    public void update();
    public void query();
}

2. Real characters

package com.kuber.dynamicdemo1;



public class UserServiceImpl implements UserService {
    
    
    public void add() {
    
    
        System.out.println("执行add方法");
    }

    public void delete() {
    
    
        System.out.println("执行delete方法");
    }

    public void update() {
    
    
        System.out.println("执行update方法");
    }

    public void query() {
    
    
        System.out.println("执行了query方法");
    }
}

3. Acting role

package com.kuber.dynamicdemo1;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class ProxyInvocationHandler implements InvocationHandler {
    
    
    /*被代理的接口*/
    private Object target;

    public void setTarget(Object target) {
    
    
        this.target = target;
    }

    /*生成得到代理类*/
    public Object getProxy(){
    
    
        return Proxy.newProxyInstance(this.getClass().getClassLoader(), target.getClass().getInterfaces(),this);
    }

    /*处理代理实例，并返回结果*/
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    
    
        log(method.getName());
        Object result = method.invoke(target, args);
        return result;
    }

    public void log(String msg){
    
    
        System.out.println("【日志】"+msg+"方法执行");
    }
}

4. Client access agent role

package com.kuber.dynamicdemo1;

public class Client {
    
    

    public static void main(String[] args) {
    
    

        /*真实角色*/
        UserServiceImpl userService = new UserServiceImpl();

        /*代理角色*/
        ProxyInvocationHandler pih = new ProxyInvocationHandler();

        /*设置要代理的对象*/
        pih.setTarget(userService);

        /*动态代理生成类*/
        UserService proxy = (UserService)pih.getProxy();
        proxy.query();
    }
}

The benefits of dynamic agents:

• Can make the operation of real characters more pure! No need to pay attention to some public business
• Public business is left to the agent role! Realize the division of labor
• When public business expands, it is convenient for centralized management.
• A dynamic proxy class proxy is an interface, generally a corresponding type of business
• A dynamic proxy class can proxy multiple classes, as long as the same interface is implemented