<form action="/StrutsFileUpAndDown/register.do" method="post" enctype="multipart/form-data">
 名字：<input type="text" name="name" />
 头像:<input type="file" name="file"/>
 <input type="submit" value="注册用户">
 </form>

/*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package com.yourcompany.struts.form;
 
import javax.servlet.http.HttpServletRequest;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.upload.FormFile;
 
/**
 * MyEclipse Struts
 * Creation date: 08-24-2017
 *
 * XDoclet definition:
 * @struts.form name="userForm"
 */
public class UserForm extends ActionForm {
 /*
  * Generated Methods
  */
 
 private String username;
 private FormFile file;
  
 public String getUsername() {
  return username;
 }
 public void setUsername(String username) {
  this.username = username;
 }
 public FormFile getFile() {
  return file;
 }
 public void setFile(FormFile file) {
  this.file = file;
 }
 
}

UserForm userForm = (UserForm) form;
String username = userForm.getUsername();
FormFile file = userForm.getFile();
 
//通过formFile可以获取关于用户上传文件的各种信息
//用于获取文件名字
String fileName = file.getFileName();
//用于获取文件大小
int fileSize = file.getFileSize();

try {
 //获取输入流
 is = file.getInputStream();
 
 //得到输出流
 //1.得到file文件夹，上传到tomcat服务器后的绝对路径(file文件为新创建的文件夹）
 String filePath = this.getServlet().getServletContext().getRealPath("/file");
 //两个"//"的其中一个"/"为转义符
  os=new FileOutputStream(filePath+"\"+fileName);
  
 int len=0;//表示读取的字节
 //做一个缓存，防止文件过大而造成错误
 byte[] buff=new byte[1024];
 while((len=is.read(buff))!=-1)
 {
  os.write(buff,0,len);
 }
 is.close();
 os.close();
}