spring 注入问题 （AOP 动态代理）

Unable to instantiate Action, com.pp.action.user.LoginAction,  defined for 'login' in namespace '/user'Error creating bean with name 'com.pp.action.user.LoginAction': Injection of resource fields failed; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'accountDao' must be of type [com.pp.dao.account.AccountDaoImpl], but was actually of type [com.sun.proxy.$Proxy19]
	com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:318)
	com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:399)
	com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:198)
	org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
	org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
	com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:58)
	org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:475)
	org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
	org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)

报错原因：

	@Resource
	private AccountDaoImpl accountDao;

	@SuppressWarnings("unchecked")
	@Action(value = "login", results = {
			@Result(name = "success", type = "json"),
			@Result(name = "fail", type = "json") })
	public String login() throws Exception {
		System.out.println("test: LoginAction---");
		String result = null;
		Account account = accountDao.getAccountByName(name);
		if (account == null) {
			result = "fail";
			flag = "pass";
		} else if (account.getPwd().equalsIgnoreCase(pwd)) {
			result = "success";
			nickName = account.getName();
			flag = "success";		
			try {
				session.put("account", account);
			} catch (Exception e) {
				// TODO: handle exception
				e.printStackTrace();
			}
		} else {
			result = "fail";
			flag = "fail";
		}
		return result;
	}

注入时 accountDao 类型 改为 其接口，

	@Resource
	private AccountDao accountDao;

就ok了

这里面主要涉及到了spring AOP的动态代理：
Spring 有两种代理：动态代理和CGLIB代理（上面的代码中用的是动态代理）：

•         动态代理只能对实现了接口的类生成代理，而不能针对类；
•         CGLIB代理是针对类实现代理，主要是对指定的类生成一个子类，覆盖其中的方法。