ajax验证某个值是否存在

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     public String viewServerCode() throws Exception{HttpServletResponse response = ServletActionContext.getResponse();   response.setContentType("text/xml; charset=UTF-8");response.setHeader("Cache-Control", "no-cache");PrintWriter out = response.getWriter();boolean bool = accountService.getValidateServer(code);String str = "";str +="<root>";if(bool){str += "<message>1</message>";}else{str += "<message>0</message>";}str += "</root>";System.out.println(str);out.print(str);out.close();return null;}

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