ajax跨区域报错

1.ajax跨区域报错：No 'Access-Control-Allow-Origin' header is present on the requested resource.

解决方法：设置head：resp.setHeader("Access-Control-Allow-Origin", "localhost");（注：localhost为ip，或直接设置为“*”）
如果请求头有传递参数，还要设置resp.setHeader("Access-Control-Allow-Headers", "*");

 设置dataType: "jsonp"


2.ajax跨区域返回时报错：Uncaught SyntaxError: Unexpected token :
解决方法：(后台代码)
   String callback = req.getParameter("callback");
            PrintWriter writer = resp.getWriter();
            writer.println(callback + "(" + jsonObject + ")");
   writer.flush();
            writer.close();