"How to use" agent mode

This paper

Provide a placeholder or stand in for an object , To control access to this object ;
Use proxy mode to create proxy objects , The proxy object is used to access the proxy object . The proxied object can be a remote object 、 Objects that are expensive to create 、 Objects requiring security control .

• Remote agent
  Remote agent as another JVM Local representation of objects on . When calling a method on the proxy , The remote agent transmits the request to the remote through the network , And then transmit the results to the local through the network , And return it to the caller .

• Virtual agent
  Virtual agents represent objects that are expensive to create . Virtual agents often wait until we really need an object , To create this object . Before the object is created 、 When creating , Access to this object is represented by virtual agents . After the object is created , The virtual agent will delegate the access of the object to the object it represents .

  • The caching proxy （Caching Proxy）
    Provide temporary storage for expensive calculation results ： It also allows multiple customers to share results , To reduce computing or network latency .

• Protection agency
  According to different permissions , Control access to the proxied object .

  • Firewall proxy （Firewall Proxy）
    Controls access to network resources , Protect “ The theme ” Free from “ Bad customer ” The effects of .
  • Intelligent reference agent (Smart Reference Proxy)
    When the topic is referenced , Perform additional actions , For example, count the number of times an object is referenced .

principle

Example

//subject
public interface PersonBean {
    
    String getName();
}
//real subject
public class PersonBeanImpl implements PersonBean {
    
    private String name;
    
    @Override
    public String getName() {
    
        return name;
    }
}
//handler
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
public class NotOwnerInvocationHandler implements InvocationHandler {
    
	// hold project
    private PersonBean personBean;

    NotOwnerInvocationHandler(PersonBean personBean) {
    
        this.personBean = personBean;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    
        if ("getIdCard".equals(method.getName())){
    
            throw new IllegalArgumentException(" It's not your information , What do you look at? ");
        }
        return method.invoke(personBean,args);
    }
}

import java.lang.reflect.Proxy;
public class ProxyUtil {
    

    public static PersonBean getOwnerProxy(PersonBean personBean){
    
        return (PersonBean) Proxy.newProxyInstance(
                personBean.getClass().getClassLoader(),
                personBean.getClass().getInterfaces(),
                new OwnerInvocationHandler(personBean)
        );
    }

    public static PersonBean getNotOwnerProxy(PersonBean personBean){
    
        return (PersonBean) Proxy.newProxyInstance(
                personBean.getClass().getClassLoader(),
                personBean.getClass().getInterfaces(),
                new NotOwnerInvocationHandler(personBean)
        );
    }
}

//test
private void drive(){
    
     PersonBean tom = new PersonBeanImpl("tom");

     PersonBean ownerProxy = ProxyUtil.getOwnerProxy(tom);
     System.out.println("ownerProxy.getIdCard() = " + ownerProxy.getIdCard());

     PersonBean notOwnerProxy = ProxyUtil.getNotOwnerProxy(tom);
     try {
    
         System.out.println("notOwnerProxy = " + notOwnerProxy.getIdCard());
     } catch (Exception e) {
    
         e.printStackTrace();
     }
}

summary

• You think you use Object, But in fact, you use ProxyObject.“I am watching you , I can touch you .’”
• Proxy and InvocationHandler All in java.lang.reflect
• Proxy Create proxy object ,InvocationHandler You can decide whether to actually delegate the request to the proxy object .

Q&A