ajax跨域访问--. No 'Access-Control-Allow-Origin

js:

   var url = "http://172.16.3.25:8090/Project/oimReceive/uploadBase64ImgByCrossDomain";
$.ajax({
type: "POST",
url:url,
data:{"img":imgdata},
dataType: 'json',
async: true,
cache: true,
success: function(data) {
//获取返回的data数据
}
});
JAVA:

/**
* IM设置更新 支持跨域
*/
@RequestMapping(value = "uploadBase64ImgByCrossDomain", method=RequestMethod.POST)
@ResponseBody
public HashMap<String, String> uploadBase64ImgByCrossDomain(String img,String sessionId,Model model,HttpServletResponse response) {
response.addHeader("Access-Control-Allow-Origin", "*"); //用于ajax post跨域（*，最好指定确定的http等协议+ip+端口号）
HashMap<String, String> dataMap = new HashMap<String, String>();
String attachmentId = generateImage(img,sessionId);
dataMap.put("attachmentId", attachmentId);
return dataMap;
}