ajax请求成功 死活不走success 只走error 返回状态码200。。请求已成功 也拿到数据，但是就是不走回调函数success。跪求大神指导

action代码

public String IndexCount(){

HttpServletResponse response=ServletActionContext.getResponse();

response.setContentType("text,html;charset=utf-8");

try {

PrintWriter out=response.getWriter();

StringBuffer indexString = new StringBuffer();

//获取前台事项类型

//查询当前事项类型的数量

int count=articleMng.FindDefStr6(defstr6);

int sumCount = articleMng.MaxCount();

//当前事项流水号

String counta=Utils.getSequence(String.valueOf(count+1));

//总流水号

String countb=Utils.getSequence(String.valueOf(sumCount+1));

//设置日期格式

SimpleDateFormat df = new SimpleDateFormat("yyyy");

indexString.append("AD2")

.append(defstr7)

.append(defstr5)

.append(defstr6)

.append(counta)

.append(df.format(new Date()))//获取当前年份

.append(countb);

System.out.println(indexString.toString());

defstr8=indexString.toString();

out.print(defstr8);

} catch (IOException e) {

e.printStackTrace();

}

return null;

}

请求代码

function indexCount(){

var derstr7=document.getElementById("bean.defStr7").value;

var derstr5=document.getElementById("bean.defStr5").value;

var derstr6=document.getElementById("bean.defStr6").value;

$.ajax({

type: "POST",

url: "${base}/admin/article/article/Com_IndexCount.do",

data:{

defstr7:derstr7,

defstr5:derstr5,

defstr6:derstr6,

},

datatype:'html',

success: function(data){

console.log("执行了");

alert(data);

},

error:function(XMLHttpRequest, textStatus, errorThrown){

alert ("XMLHttpRequest.status="+XMLHttpRequest.status+"\ntextStatus="+textStatus+"\nerrorThrown=" + errorThrown);

}

});

}

后台正常输入

前台走了error弹窗

浏览器调试 显示已拿到值，但是不走success