In -depth understanding of SpringFramework Aop: The bottom layer of cutting programming in the Java class library realizes the original
In -depth understanding of Spring Framework Aop: Principles of the bottom layer of cutting programming in the Java class library
preface:
In Java's development, ASPECT-Oriented Programming (AOP) has become a common programming paradigm.Spring Framework is a popular Java framework that provides convenient and powerful AOP support.This article will explore the principles of the underlying implementation of the Spring Framework Aop and explain it through the Java code example.
What is AOP?
Before understanding the Spring Framework Aop, we need to understand the concept of AOP first.AOP is a programming method for cutting surface. By being separated from the main business logic, each follow-up point can be maintained and reused by separating the cross-cutting concern.The horizontal cutting attention points include log records, transaction management, safety inspections, etc.AOP allows us to better decoup the different parts of the application and improve the maintenance and replication of code.
Basic concept of Spring Framework Aop:
Spring Framework Aop is an agent -based AOP implementation method.In Spring, the proxy consists of two main components: target object and enhanced objects.The target object is an enhanced object, and the enhanced object defines the code logic that is executed before, after, or before and after the target object method.
In Spring Framework, the cut surface is a class containing enhanced logic.One cut surface can contain multiple enhanced objects, and each enhanced object corresponds to a specific pointcut.Cut the point defines the enhancement logic in which methods of the target object.
Principles of the underlying implementation of Spring Framework Aop:
The bottom layer of Spring Framework Aop implements dynamic proxy technology and reflection mechanisms.During the AOP woven process, Spring dynamically enhances the logic into the target object by creating a proxy object by creating a proxy object for target objects.
Spring Framework supports two types of AOP agents: JDK dynamic agent and CGLIB agent.The JDK dynamic proxy requires the target object to implement one or more interfaces, while the CGLIB proxy does not need.When running, Spring selects the appropriate proxy type based on the configuration.
Java code example:
Below is a simple Java code example, demonstrating the use of Spring Framework Aop:
// target
public interface UserService {
void addUser(String username);
void deleteUser(String username);
}
// Realization of the target object
public class UserServiceImpl implements UserService {
public void addUser(String username) {
System.out.println ("Add user:" + username);
}
public void deleteUser(String username) {
System.out.println ("Delete user:" + username);
}
}
//
@Aspect
public class LoggingAspect {
@Before("execution(* com.example.UserService.addUser(String))")
public void beforeAddUser(JoinPoint joinPoint) {
System.out.println ("Preliminary Enhancement: Before calling adduser method");
}
@After("execution(* com.example.UserService.addUser(String))")
public void afterAddUser(JoinPoint joinPoint) {
System.out.println ("rear enhancement: after call adduser method");
}
}
// Configuration file
@Configuration
@EnableAspectJAutoProxy
public class AppConfig {
@Bean
public UserService userService() {
return new UserServiceImpl();
}
@Bean
public LoggingAspect loggingAspect() {
return new LoggingAspect();
}
}
// The main method
public class Main {
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
UserService userService = context.getBean(UserService.class);
userService.addUser("Alice");
userService.deleteUser("Bob");
}
}
In this example, we define an interface `userService` and its implementation class` userServiceImpl` as the target object.By define the enhanced logic in the cut surface of the `Loggingaspect`, and use the annotation`@aspect` to identify this class as the cut surface.
Use annotations `@before` and`@after` to define the enhanced logic of execution before and after the implementation of the target object.Note that we can use the information of the `Joinpoint` parameter.In the `APPCONFIG` configuration class, we enable the Spring AOP function through the`@encableaspectjautoProxy`.
In the main method of `Main`, we use the` AnnotationConfigApplicationContext` to create a Spring application context and obtain the `userService` instance.Finally, we call the method of `UserService` to trigger AOP enhanced logic.
in conclusion:
Spring Framework Aop is a powerful and flexible AOP implementation, and its underlying implementation is based on agency and reflection mechanism.By understanding the principle of Spring Framework AOP, we can better use and expand this function, thereby improving the reuse and maintenance of Java applications.
