Ext doAction提交json参数后台接收为乱码解决方案

在websphere服务器上，客户端提交json代码，后台接收为中文字母为乱码，为这个问题没少查阅资料，在参考对比Ext.Ajax.request方法时，豁然发现传递json参数方式有问题，细微差别，导出出现不同的问题，详细代码如下：

loginForm.form.doAction('submit',{
                                           url:'purchaseApplyToOrder.do',
                                            method:'post',
                                        //    params:'json='+json,  //错误提交json参数，导致后台接收中文字母为乱码
                                            params:{json:json},   //正确提交json参数
                                            timeout: 999999999999999999,
                                            waitMsg:'正在提交．．．．．．',
                                            waitTitle :'等待',
                                            success:function(form,actionReturned){
             Ext.MessageBox.alert('信息提示',"成功,申请编号:"+actionReturned.result.successful,function(){
                                                parent.parent.search();
                                                         parent.parent.win.close();
                 
                                                     });
             this.disabled=true;
                             },
                                      failure:function(form, actionReturned){
                                        if(actionReturned.result!=null){
              Ext.MessageBox.alert('信息提示',actionReturned.result.error,function(){
                                                parent.parent.search();
                                                         parent.parent.win.close();
                 
                                                     });
                                              }else{ 
                                            Ext.MessageBox.alert('信息提示','请求超时，请刷新！',function(){
                                                parent.parent.search();
                                                         parent.parent.win.close();
                 
                                                     });
                                               this.disabled=false;
                                               
                                            }
                                          }
                         })