java动态代表类

主要用途针对某些业务场景进行前或后的特殊业务的验证，如删除用户时确保该用户存在

public class Client {

	public static void main(String[] args) {
		//UserManager userManager = new UserManagerImpl();
		
		SecurityHandler handler = new SecurityHandler();
		UserManager userManager = (UserManager)handler.newProxy(new UserManagerImpl());
		
		//userManager.addUser("张三", "123");
		userManager.deleteUser(1);
	}
}

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

public class SecurityHandler implements InvocationHandler {

	private Object targetObject;
	
	public Object newProxy(Object targetObject) {
		this.targetObject = targetObject;
		return Proxy.newProxyInstance(targetObject.getClass().getClassLoader(), 
									  targetObject.getClass().getInterfaces(), 
									  this);
					
	}
	
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		checkSecurity();
		Object ret = null;
		try {
			ret = method.invoke(this.targetObject, args);
		}catch(Exception e) {
			e.printStackTrace();
			throw new java.lang.RuntimeException(e);
		}
		return ret;
	}

	private void checkSecurity() {
		System.out.println("----------checkSecurity()---------------");
	}
	
}

public interface UserManager {

	public void addUser(String username, String password);
	
	public void deleteUser(int id);
	
	public void modifyUser(int id, String username, String password);
	
	public String findUserById(int id);
}

public class UserManagerImpl implements UserManager {

	public void addUser(String username, String password) {
		System.out.println("-------UserManagerImpl.addUser()----------");
	}

	public void deleteUser(int id) {
		System.out.println("-------UserManagerImpl.deleteUser()----------");
	}

	public String findUserById(int id) {
		System.out.println("-------UserManagerImpl.findUserById()----------");
		return null;
	}

	public void modifyUser(int id, String username, String password) {
		System.out.println("-------UserManagerImpl.modifyUser()----------");
	}
	
}