117笔记问答Java动态代理可以通过以下几种方式实现：
- 使用
java.lang.reflect.Proxy类：Proxy类提供了一个静态方法newProxyInstance()，可以通过传入目标对象的类加载器、目标对象实现的接口和InvocationHandler接口的实现类来创建代理对象。InvocationHandler接口的实现类负责处理代理对象的方法调用。代理对象在调用方法时，会把方法调用转发给InvocationHandler的invoke()方法，从而实现代理功能。
public interface Subject {
void doSomething();
}
public class RealSubject implements Subject {
public void doSomething() {
System.out.println("RealSubject doSomething");
}
}
public class MyInvocationHandler implements InvocationHandler {
private Subject target;
public MyInvocationHandler(Subject target) {
this.target = target;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("Before method invoke");
Object result = method.invoke(target, args);
System.out.println("After method invoke");
return result;
}
}
public class Main {
public static void main(String[] args) {
Subject realSubject = new RealSubject();
Subject proxySubject = (Subject) Proxy.newProxyInstance(realSubject.getClass().getClassLoader(),
realSubject.getClass().getInterfaces(),
new MyInvocationHandler(realSubject));
proxySubject.doSomething();
}
}
- 使用
CGLib库：CGLib是一个基于ASM框架的字节码生成库，它可以在运行时动态生成目标对象的子类，并覆盖其中的方法以实现代理功能。
public interface Subject {
void doSomething();
}
public class RealSubject implements Subject {
public void doSomething() {
System.out.println("RealSubject doSomething");
}
}
public class MyMethodInterceptor implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("Before method invoke");
Object result = proxy.invokeSuper(obj, args);
System.out.println("After method invoke");
return result;
}
}
public class Main {
public static void main(String[] args) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(RealSubject.class);
enhancer.setCallback(new MyMethodInterceptor());
Subject proxySubject = (Subject) enhancer.create();
proxySubject.doSomething();
}
}
需要注意的是，使用CGLib实现动态代理时，目标对象不能是final类或者包含final方法，因为CGLib是通过生成目标对象的子类来实现代理的。
- 使用
ByteBuddy库：ByteBuddy是一个轻量级的字节码操作库，它可以在运行时动态生成目标对象的子类，并覆盖其中的方法以实现代理功能。
public interface Subject {
void doSomething();
}
public class RealSubject implements Subject {
public void doSomething() {
System.out.println("RealSubject doSomething");
}
}
public class MyInterceptor implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("Before method invoke");
Object result = proxy.invokeSuper(obj, args);
System.out.println("After method invoke");
return result;
}
}
public class Main {
public static void main(String[] args) throws Exception {
Class proxyClass = new ByteBuddy()
.subclass(Subject.class)
.method(any()).intercept(MethodDelegation.to(MyInterceptor.class))
.make()
.load(RealSubject.class.getClassLoader())
.getLoaded();
Subject proxySubject = proxyClass.getDeclaredConstructor().newInstance();
proxySubject.doSomething();
}
}
需要注意的是，使用ByteBuddy实现动态代理时，需要引入net.bytebuddy:byte-buddy和net.bytebuddy:byte-buddy-agent两个依赖。