Ext.Ajax获取返回值（参数）

Ext.Ajax.request({
url:'http://localhost:8080/myapp/ExtHandler,
jsonData:Ext.util.JSON.encode(info),
params:{action:'up'},
success: function(resp,opts) {
var respText = Ext.util.JSON.decode(resp.responseText);
Ext.Msg.alert('提示', respText.info);
},
failure: function(resp,opts) {
var respText = Ext.util.JSON.decode(resp.responseText);
Ext.Msg.alert('错误', respText.error);
}
});

StringBuffer json = new StringBuffer();
String line = null;
try {
BufferedReader reader = req.getReader();
while ((line = reader.readLine()) != null)  {
//读取jsonData中定义的数据
json.append(line);
}
} catch (Exception e) {
}

rsp.setContentType("text/json; charset=utf-8");
rsp.getWriter().write(
"{success:false,error:'更新信息失败，原因为:" + err + "'}");
rsp.setStatus(HttpServletResponse.SC_EXPECTATION_FAILED);     //设置失败标识
//failure回调函数将调用执行，输出respText.error信息