Java中通过反射实现代理Proxy代码实例

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
public class ProxyHandler implements InvocationHandler {
    private UserService object;
    public ProxyHandler() {
        this.object = new UserServiceImpl();
    }
    public UserService newProxyInstance(){
        return (UserService) Proxy.newProxyInstance(this.object.getClass().getClassLoader(), this.object.getClass().getInterfaces(), this);
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("预处理");
        Object object = method.invoke(this.object, args);
        if(object instanceof Person) {
            ((Person) object).setName("姓名：" + ((Person) object).getName());
        }
        System.out.println("后处理");
        return object;
    }
}

public class Test {
    public static void main(String[] args) {
        ProxyHandler proxyHandler = new ProxyHandler(); //生成代理类初始化被代理类
        UserService userService = proxyHandler.newProxyInstance(); //生成代理实例
        System.out.println(userService.getUserInfo(1).getName()); //调用被代理方法
    }
}

public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {
        Objects.requireNonNull(h);
        final Class<?>[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }
        /*
         * 从缓存中获取到代理类
         */
        Class<?> cl = getProxyClass0(loader, intfs);
        try {
            if (sm != null) {
                checkNewProxyPermission(Reflection.getCallerClass(), cl);
            }
            final Constructor<?> cons = cl.getConstructor(constructorParams);//获取到代理类的构造器
            final InvocationHandler ih = h;
            if (!Modifier.isPublic(cl.getModifiers())) {
                AccessController.doPrivileged(new PrivilegedAction<Void>() {
                    public Void run() {
                        cons.setAccessible(true);
                        return null;
                    }
                });
            }
            return cons.newInstance(new Object[]{h});//生成代理类实例
        } catch (IllegalAccessException|InstantiationException e) {
            throw new InternalError(e.toString(), e);
        } catch (InvocationTargetException e) {
            Throwable t = e.getCause();
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new InternalError(t.toString(), t);
            }
        } catch (NoSuchMethodException e) {
            throw new InternalError(e.toString(), e);
        }
    }

 private static Class<?> getProxyClass0(ClassLoader loader,
                                           Class<?>... interfaces) {
        if (interfaces.length > 65535) {
            throw new IllegalArgumentException("interface limit exceeded");
        }
        // If the proxy class defined by the given loader implementing
        // the given interfaces exists, this will simply return the cached copy;
        // otherwise, it will create the proxy class via the ProxyClassFactory
        return proxyClassCache.get(loader, interfaces);
    }
 private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
        proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());