easyui combobox trigger  onLoadError event constantly.

The problem remains.
<input id="codeNameCheckbox" class="easyui-combobox" name="codeName"                             
                      data-options="
                         panelHeight:'150',url:'${path}/face/getCodesByAttrs.do',
                            fit:true,editable:false, method: 'get',                            
                                valueField:'value',
                                  textField:'text' " />

Could someone help me?

java
getCodesByAttr(){
     response.setHeader("Content-type", "application/json");   
    out.write(json);
    out.flush();
}
               
Above is a json string written to the page json:"[{'text':'China,'value':'1'},{'text':'Japan','value':'2'}]"


jsp
<input id="codeNameCheckbox" class="easyui-combobox" name="codeName"             
          url:'/getCodesByAttrs.do',
             fit:true,editable:false,                       
                   valueField:'value',
                      textField:'text' />


Why easyui combobox trigger  onLoadError event ?
 

Could someone help me?

java
getCodesByAttr(){
     response.setHeader("Content-type", "application/json");  
    out.write(json);
    out.flush();
}
                
Above is a json string written to the page json:"[{'text':'China,'value':'1'},{'text':'Japan','value':'2'}]"


jsp
<input id="codeNameCheckbox" class="easyui-combobox" name="codeName"            
          url:'/getCodesByAttrs.do',
             fit:true,editable:false,                        
                   valueField:'value',
                      textField:'text' />


Why easyui combobox trigger  onLoadError event ?