How to use dynamic proxy in Spring

Steps to use dynamic proxy in Spring: 1. Define an interface; 2. Create a target class; 3. Create a proxy class; 4. Configure notifications; 5. Run the application. Detailed introduction: 1. To define an interface, you first need to define an interface, which will be implemented by the proxy object. This interface defines the behavior that you want to execute before, after, and when an exception is thrown; 2. Create a target class, create a target class MyServiceImpl that implements the MyService interface. This class contains what you want to do before the method is called, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

In the Spring framework, dynamic proxy is a commonly used technology for dynamically creating proxy objects at runtime in order to implement AOP (aspect-oriented programming) functions. Dynamic proxies allow programmers to define cross-cutting concerns that can execute specific code before and after a method is called, when an exception is thrown, when executing within a transaction, etc.

The following are the steps to implement AOP in Spring using dynamic proxy:

1. Define an interface: First, you need to define an interface, which will be implemented by the proxy object . This interface defines the behavior you want to perform before and after method calls, when exceptions are thrown, etc. For example, you can define an interface named MyService that contains a doSomething() method.

public interface MyService {  
    void doSomething();  
}

2. Create a target class: Create a target class MyServiceImpl that implements the MyService interface. This class contains the code you want to execute before, after, etc. the method is called.

public class MyServiceImpl implements MyService {  
    public void doSomething() {  
        System.out.println("Doing something...");  
    }  
}

3. Create a proxy class: Use the AOP framework provided by Spring to create a proxy class. Spring provides two types of dynamic proxies: JDK dynamic proxies and CGLIB dynamic proxies. Here we take the JDK dynamic proxy as an example and use ProxyFactoryBean to create a proxy class MyServiceProxy.

import org.springframework.aop.framework.ProxyFactoryBean;  
import org.springframework.context.annotation.Bean;  
import org.springframework.context.annotation.Configuration;  
  
@Configuration  
public class AppConfig {  
    @Bean  
    public MyService myService() {  
        return new MyServiceImpl();  
    }  
  
    @Bean  
    public MyServiceProxy myServiceProxy() {  
        ProxyFactoryBean factory = new ProxyFactoryBean();  
        factory.setTargetBeanName("myService"); // 指定目标对象的名字  
        factory.addAdvice(new SimpleTraceInterceptor()); // 添加通知，定义在方法调用之前、之后等场景中执行的代码  
        return (MyServiceProxy) factory.getObject(); // 获取代理对象  
    }  
}

4. Configuration notification: In the proxy class, you need to configure the notification (Advice) to define the code to be executed before and after the method is called. Here we use SimpleTraceInterceptor as an example, which will output logs before and after method calls. You can customize the notification implementation as needed.

5. Run the application: Start the application and test whether the dynamic proxy works as expected. You can verify that the notification executed correctly by calling various methods on the target object. In the above example, when myServiceProxy().doSomething() is called, the log "Doing something..." will be output, and the corresponding logs will be output before and after the method call.

In addition to the JDK dynamic proxy used in the above example, Spring also provides CGLIB dynamic proxy as another option. CGLIB dynamic proxy is suitable for classes that do not implement interfaces. The class file of the proxy object class is loaded through the bytecode processing framework asm, and subclasses are generated by modifying the bytecode. The configuration method of using CGLIB dynamic proxy is similar to that of JDK dynamic proxy, except that different classes or configuration methods need to be used when creating proxy objects.

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