代理类热重载

代理类热重载非常重要，因为 Spring 和 MyBatisPlus 等都是通过代理类对代码进行增强。

JDK

定义接口

public interface UserService {

    void addUser(String name);

}

定义实现类

public class UserServiceImpl implements UserService {

    @Override
    public void addUser(String name) {
        System.out.println("Add user: " + name); 
        printName(name); 
    }
    
    public void printName(String name) { 
        System.out.println("printName: " + name); 
    } 
}

定义 InvocationHandler

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class UserServiceInvocationHandler implements InvocationHandler {

    private final Object target;

    public UserServiceInvocationHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getName().equals("addUser")) {
            System.out.println("Before method: " + method.getName()); 
            printName("Before", method.getName()); 
            Object result = method.invoke(target, args);
            System.out.println("After method: " + method.getName()); 
            printName("After", method.getName()); 
            return result;
        } else {
            return method.invoke(target, args);
        }
    }
    
    private void printName(String hook, String name) { 
        System.out.println(hook + " printName :" + name); 
    } 
}

使用 Proxy 创建代理对象

import java.lang.reflect.Proxy;

public class ProxyTest {

    public static void main(String[] args) throws InterruptedException {
        // 创建目标对象
        UserService target = new UserServiceImpl();

        // 创建 InvocationHandler
        UserServiceInvocationHandler handler = new UserServiceInvocationHandler(target);

        // 创建代理对象
        UserService proxy = (UserService) Proxy.newProxyInstance(
                target.getClass().getClassLoader(),
                target.getClass().getInterfaces(),
                handler
        );

        while (true) {
            Thread.sleep(10000);
            // 调用代理对象的方法
            proxy.addUser("DebugTools");
        }
    }
}

打印执行

# 热重载之前
Before method: addUser
Add user: DebugTools
After method: addUser
# 热重载之后
Before printName: addUser
printName: DebugTools
After printName: addUser

Cglib

创建代理对象

public class UserService {

    public void addUser(String name) {
        System.out.println("Add user: " + name); 
        printName(name); 
    }

    public void printName(String name) { 
        System.out.println("printName: " + name); 
    } 
}

编写方法拦截器

import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;

public class UserServiceInterceptor implements MethodInterceptor {

    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        if (method.getName().equals("addUser")) {
            System.out.println("Before method: " + method.getName()); 
            printName("Before", method.getName()); 
            Object result = proxy.invokeSuper(obj, args);
            System.out.println("After method: " + method.getName()); 
            printName("After", method.getName()); 
            return result;
        } else {
            return proxy.invokeSuper(obj, args);
        }
    }

    private void printName(String hook, String name) { 
        System.out.println(hook + " printName :" + name); 
    } 
}

使用 Enhancer 动态生成代理类：

import net.sf.cglib.proxy.Enhancer;

public class ProxyTest {

    public static void main(String[] args) throws InterruptedException {
        // 创建 Enhancer 对象
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(UserService.class);
        enhancer.setCallback(new UserServiceInterceptor());
        UserService proxy = (UserService) enhancer.create();
        while (true) {
            Thread.sleep(1000);
            // 调用代理对象的方法
            proxy.addUser("DebugTools");
        }
    }
}

打印执行

# 热重载之前
Before method: addUser
Add user: DebugTools
After method: addUser
# 热重载之后
Before printName: addUser
printName: DebugTools
After printName: addUser