Detailed explanation of java dynamic proxy mode

This article organizes knowledge points on java dynamic proxy. The specific content is as follows

1. JAVA dynamic proxy (more official statement)
The proxy mode is a commonly used java design pattern, and its characteristic is proxy The class has the same interface as the delegate class. The proxy class is mainly responsible for preprocessing messages for the delegate class, filtering messages, forwarding messages to the delegate class, and processing messages afterwards. There is usually an association between a proxy class and a delegate class. An object of a proxy class is associated with an object of a delegate class. The object of the proxy class itself does not actually implement the service, but by calling the relevant methods of the object of the delegate class. Provide specific services.
According to the creation period of the agent, the agent class can be divided into two types.
Static proxy: Created by programmers or automatically generated by specific tools, and then compiled. Before the program is run, the .class file of the proxy class already exists.
Dynamic proxy: Dynamically created using the reflection mechanism when the program is running.

2. Dynamic proxy implementation

java.lang.reflect.Proxy,
Proxy provides static methods for creating dynamic proxy classes and instances.
newProxyInstance()
Returns a proxy class instance of the specified interface, which can assign method calls to the specified call handler.

2.1. Dao interface (providing simulated data access layer interface)

package javaproxy;
/*
 * 定义一个数据访问层接口
 */
public interface Dao {
 //模拟数据保存
public void save();
}

2.2. DaoImpl class implementation class

package javaproxy;
  
public class DaoImpl implements Dao{
  
 @Override
 public void save() {
  System.out.println("执行一个保存方法。。。。。。。。。。。。");
    
 }
  
}

2.3. Agent processing class

package javaproxy;
  
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
  
public class DaoHandler implements InvocationHandler{
 private Object obj;
public DaoHandler(Object obj) {
 this.obj=obj;
}
 @Override
 public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
   System.out.println("do something before method");//这里模拟AOP的前置方法
   Object ret = method.invoke(this.obj, args);
   System.out.println("do something after method");//这里模拟AOP的后置方法
   return ret;
 }
  
}

2.4. Client call

package javaproxy;
  
import java.lang.reflect.Proxy;
  
public class Client {
    
  public static void main(String[] args) {
   // 元对象(被代理对象)
   DaoImpl daoImpl = new DaoImpl();
    
   // 业务代理类
   DaoHandler daoHandler=new DaoHandler(daoImpl);
    
   Dao dao=(Dao) Proxy.newProxyInstance(daoImpl
    .getClass().getClassLoader(), daoImpl.getClass()
    .getInterfaces(), daoHandler);
    
   dao.save();
  
 }
}

2. 5. Result

3 . Simulate the proxy implementation in Mybatis

3.1. MapperProxy class

package javaproxy;
 
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
 
public class MapperProxy implements InvocationHandler {
 @SuppressWarnings("unchecked")
 /*
  * 这里通过静态方法得到实现类的对象
  *
  * @param：接口
  *
  * @param：用sqlsession执行方法
  *
  * @return: 返回代理对像
  */
 public static <T> T newMapperProxy(Class<T> mapperInterface,
   Object sqlSession) {
  ClassLoader classLoader = mapperInterface.getClassLoader();
  Class<?>[] interfaces = new Class[] { mapperInterface };
  MapperProxy proxy = new MapperProxy();
  return (T) Proxy.newProxyInstance(classLoader, interfaces, proxy);
 }
 
 /*
  * (non-Javadoc)
  *
  * @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object,
  * java.lang.reflect.Method, java.lang.Object[])
  *
  * @param：代理对象
  *
  * @param：方法通过方法名字找到对应的方法
  *
  * @param：通过方法传入对象找到对应的传递参数映射
  *
  * @return：返回执行后的参数对象
  */
 public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
  // 这里通过方法名字以及参数通过解析对应的mapper来执行对应的操作
  System.out.println("在这里执行实际方法");
  return null;
 }
 
}

3.2. Client

package javaproxy;
  
import java.lang.reflect.Proxy;
  
public class Client {
    
  public static void main(String[] args) {
    
  Dao dao=MapperProxy.newMapperProxy(Dao.class, null);
  dao.save();
  
 }
}

3.3. Result

The above are examples of using JDK dynamic proxy. I hope it will be helpful for everyone to learn java programming.

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