The standard way to tackle AJAX calls with JSON results in my current project uses an extended version of Spring’s JsonView class. It worked quite well until I used an ExtJS FormPanel with the property fileUpload set to true. Have a look at the code bellow and then I’ll describe the problem.

The panel looks like:

var uploadOuterPanel = new Ext.FormPanel( {
   fileUpload :true,
   // Other properties omitted
   items : {
      allowBlank :false,
      id :'file',
      inputType :'file',
      name :'myFile',
      fieldLabel :'File',
      blankText :'Please choose a file',
      anchor :'95%',
      required :true,
      autoShow :true,
      xtype :'textfield'
   },
   buttonAlign: 'left',
   buttons : [ {
      text :'Upload',
      handler : function() {
         if (uploadOuterPanel.getForm().isValid()) {
            uploadOuterPanel.getForm().submit( {
               url :'',
               waitMsg :'Uploading your file...',
               success : function(form, action) {
                  Ext.Msg.alert('Success', 'File processed successfuly!');
               },
               failure : // Handle failure omitted
            });
         }
      }
   } ]
});

The Controller looks like: