struts上传不成功

jsp页面：
 <body>
   <form action="Upload" method="post" enctype=" multipart/form-data">
     <input type="file" name="fileupload"/><br>
     <input type="submit" value="O K"/>
   </form>
  </body>action:
package com.sasu.action;import java.io.File;import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;@SuppressWarnings("serial")
public class RegisterAction extends ActionSupport {
public RegisterAction(){

}
private File fileupload;
private String fileuploadContentType;
private String fileuploadFileName;
public File getFileupload() {
return fileupload;
} public void setFileupload(File fileupload) {
this.fileupload = fileupload;
} public String getFileuploadContentType() {
return fileuploadContentType;
} public void setFileuploadContentType(String fileuploadContentType) {
this.fileuploadContentType = fileuploadContentType;
} public String getFileuploadFileName() {
return fileuploadFileName;
} public void setFileuploadFileName(String fileuploadFileName) {
this.fileuploadFileName = fileuploadFileName;
}
public String regist() throws Exception{
        String realPath = ServletActionContext.getServletContext().getRealPath("/fileupload");
        if(fileupload!=null){
         System.out.println("====="+realPath);
        File saveFile = new File(new File(realPath),fileuploadFileName);
        if(!saveFile.getParentFile().exists()){
         saveFile.getParentFile().mkdirs();
        }
        
        FileUtils.copyFile(fileupload, saveFile);
        
        }
return "success";
}}
struts.xml