Access-Control-Allow-Origin 错误

ajax 跨域请求时出现 Access-Control-Allow-Origin 错误
出现原因：在你原先的页面上原本定义有header元素，而你通过跨域请求后，是局部请求。
解决方案：
在你接收器上加上这段代码：
HttpServletResponse response = (HttpServletResponse) resp;
// 指定允许其他域名访问
response.addHeader(“Access-Control-Allow-Origin”, “*”);
// 响应类型 响应方法
response.addHeader(“Access-Control-Allow-Methods”, “POST,OPTIONS,GET”);
// 响应头设置
response.addHeader(“Access-Control-Allow-Headers”, “POWERED-BY-FANTONG”);
response.addHeader(“Access-Control-Max-Age”, “30”);
SysContent.setRequest((HttpServletRequest)req);

SysContent.java
public class SysContent {
 private static ThreadLocal<HttpServletRequest> requestLocal= new ThreadLocal<HttpServletRequest>();  
 private static ThreadLocal<HttpServletResponse> responseLocal= new ThreadLocal<HttpServletResponse>();  

public static HttpServletRequest getRequest() {  
    return (HttpServletRequest)requestLocal.get();  
}  
public static void setRequest(HttpServletRequest request) {  
    requestLocal.set(request);  
}  
public static HttpServletResponse getResponse() {  
    return (HttpServletResponse)responseLocal.get();  
}  
public static void setResponse(HttpServletResponse response) {  
    responseLocal.set(response);  
}  
public static HttpSession getSession() {  
    return (HttpSession)((HttpServletRequest)requestLocal.get()).getSession();  
}  

}
不过，建议最好写成过滤器，毕竟一般而言，项目中不止一个处理请求的servlet或者Controller ，所以减少代码量和代码的间接性，和可维护性。