关于ajax $.post() 返回乱码问题

一直出现乱码，关键在这里，请看这两段代码的区别

Gson gson = new Gson();String str = gson.toJson(users);response.setContentType("application/json; charset=utf-8");response.setHeader("pragma", "no-cache");response.setHeader("cache-control", "no-cache");PrintWriter out = response.getWriter(); out.println(str);out.flush();

Gson gson = new Gson();String str = gson.toJson(users);PrintWriter out = response.getWriter(); response.setContentType("application/json; charset=utf-8");response.setHeader("pragma", "no-cache");response.setHeader("cache-control", "no-cache");out.println(str);out.flush();

response.setContentType("application/json; charset=utf-8");//前者没有乱码，后者有乱码，关键在于这句话的位置