Spring ASM framework implements the dynamic proxy of the Java class library
Spring ASM framework implements the dynamic proxy of the Java class library
introduction:
In software development, dynamic proxy is a commonly used design mode that allows us to create an agent object during runtime. The proxy object can add some additional logic based on the original object.The Spring framework provides a dynamic proxy function based on ASM (bytecode operation framework), so that we can easily achieve dynamic proxy in the Java library.This article will introduce the implementation method of dynamic proxy using the ASM framework in the Spring framework, and provide some example code to help readers better understand.
1. What is the ASM framework?
ASM is an operating framework based on the Java bytecode. It can dynamically generate or modify the class by modifying the byte code directly.Compared with the reflex mechanism that comes with Java, ASM has better performance in performance, and can operate the class code more flexibly.The Spring framework uses the functions provided by the ASM framework to realize the mechanism of dynamic proxy.
2. The dynamic agent in the Spring framework implements the realization
The dynamic proxy function in the Spring framework can be implemented by using CGLib and ASM.CGLIB is a high -performance bytecode generating library based on ASM. Compared with the dynamic proxy in JDK, CGLIB is more powerful and better.But this article focuses on the method of using Spring to use ASM to achieve dynamic proxy.
1. Introduce Spring and ASM dependencies
In projects using the Spring framework, we first need to introduce dependence on Spring and ASM.You can automatically download related dependencies through Maven and other methods.
2. Create proxy factory category
First of all, we need to create a proxy factory class to generate proxy objects.The proxy factory class can implement the MethodInterCepTor interface provided by Spring, and enhances or modify the method by implementing the intercept method.
public class ProxyFactory implements MethodInterceptor {
private Object target;
public ProxyFactory(Object target) {
this.target = target;
}
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
// Execute some logic before the method call
System.out.println("Before method: " + method.getName());
// The method of calling the original object
Object result = method.invoke(target, args);
// Execute some logic after the method calls
System.out.println("After method: " + method.getName());
return result;
}
public Object getProxy() {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(target.getClass());
enhancer.setCallback(this);
return enhancer.create();
}
}
In the above code, we define a ProxyFactory class that accepts a target object as a parameter and implements the MethodInterceptor interface.In the intercept method, we can execute some logic before the method calls, then call the method of the original object, and finally perform some logic after the method calls.In this way, we have completed a simple dynamic proxy factory.
3. Use proxy factories to generate proxy objects
Now, we can use an agent factory to generate an agent object.First of all, we need to create a target class that needs to achieve a method we need to enhance or modify.
public interface UserService {
void addUser(String username);
}
We can then create an agency factory and generate an agent object.
public static void main(String[] args) {
UserService userService = new UserServiceImpl();
ProxyFactory proxyFactory = new ProxyFactory(userService);
UserService proxy = (UserService) proxyFactory.getProxy();
proxy.addUser("John");
}
In the above code, we instance a target object UserService and pass it as a parameter to the constructor of the agency factory.We then call the GetProxy method of the agent factory to generate proxy object Proxy.Finally, we call the adduser method of the proxy object. The proxy factory will print the "BEFORE METHOD: Adduser" and "AFTER METHOD: Adduser" before and after the method calls.
in conclusion:
The Spring framework realizes the dynamic proxy function of the Java class library by using the ASM framework.Dynamic proxy can generate or modify the byte code of the class during runtime to enhance or modify the method.Using the Spring framework agency factory category, we can easily generate dynamic proxy objects and perform some logic before and after the method call.At the same time, using the ASM framework can improve the performance of dynamic proxy, which is more flexible than the reflection mechanism comes with Java.
It is hoped that this article will help readers understand the ASM dynamic agent in the Spring framework to help readers learn how to use the Spring framework to implement the dynamic agent of the Java class library.
