求助：smartGWT form提交 servlet不能获得传值

使用smartGWT构建一个form,里面有一个文本框，一个上传文件，代码如下

String url = "/uploadimage/upload";

uploadForm.setTarget("framename");

uploadForm.setAction(url);

uploadForm.setMethod(FormMethod.POST);

uploadForm.setSize("100%", "100%");

TextItem textItem = new TextItem("abc");

		

uploadForm.setEncoding(Encoding.MULTIPART);

// uploadForm.setEncoding(Encoding.NORMAL);

textItem.setValue("123");

		

final UploadItem uploadItem = new UploadItem("file", "选择图片");

uploadForm.setFields(textItem,uploadItem);

在servlet中request取文本框里面的值为null

怎样才能获得form里文本框的值？谢谢！