怎么用拦截器知道HttpServletResponse向前台输出了内容

[theoffspring]

scenario是这样的:ajax向action发起一个业务调用,如果失败,会用HttpServletResponse向前台输出错误消息,我想用拦截器进行拦截,在不修改action的基础上,如果出现错误,做一些别的操作.

public void updateReport() throws Exception {//要调用的业务方法
		
		try {
			bo.insert(...);
			
		} catch (Exception e) {
			setResErrMsg(MessageUtil.getMessage(e.getMessage(), new Object[0]));
			
		} 

	}

protected void setResErrMsg(String errMsg) throws IOException {
		
		HttpServletResponse res = ServletActionContext.getResponse();



		res.setContentType("test/html;charset=Shift-Jis");
		OutputStreamWriter writer =
			new OutputStreamWriter(res.getOutputStream(),ApplicationInfo.getNativeEncoding());

		try {
			JSONObject obj = new JSONObject();
			obj.put("errMsg", errMsg);
			writer.write(obj.toString());
			
		} finally {
			writer.flush();
			writer.close();
		}
	}

如果实在没办法,只能重构action,加上一个标志boolean来判断了.