Example code for using fileupload component to implement file upload function in Java

package pers.msidolphin.uploadservlet.web;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.List;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
/**
 * Servlet implementation class UploadServlet
 */
public class UploadServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  /**
   * @see HttpServlet#HttpServlet()
   */
  public UploadServlet() {
    super();
  }
  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //获取解析工厂
    DiskFileItemFactory factory = new DiskFileItemFactory();
    //得到解析器
    ServletFileUpload parser = new ServletFileUpload(factory);
    //解决文件名乱码问题
    parser.setHeaderEncoding("UTF-8");
    //判断上传表单类型
    if(!ServletFileUpload.isMultipartContent(request)) {
      return;
    }
    try {
      //调用解析器解析上传数据
      List<FileItem> fileItems = parser.parseRequest(request);
      //获得保存上传文件目录的路径
      String uploadPath = request.getServletContext().getRealPath("/WEB-INF/upload");
      //遍历List集合
      for (FileItem fileItem : fileItems) {
        //判断是否为普通表单字段
        if(fileItem.isFormField()) {
          //如果是普通表单字段则打印到控制台
          if(fileItem.getString() == null || "".equals(fileItem.getString().trim())) {
            continue;
          }
          System.out.println(fileItem.getFieldName() + " = " + new String(fileItem.getString().getBytes("ISO-8859-1"), "UTF-8"));
        }else {
          //获得文件路径
          String filePath = fileItem.getName();
          //如果并未上传文件，继续处理下一个字段
          if(filePath == null || "".equals(filePath.trim())) {
            continue;
          }
          System.out.println("处理文件:" + filePath);
          //截取文件名
          String fileName = filePath.substring(filePath.lastIndexOf("\\") + 1);
          String reallyName = this.createFileName(fileName);
          String reallyPath = this.mkDir(reallyName, uploadPath);
          //下面都是普通的IO操作了
          InputStream in = fileItem.getInputStream();
          FileOutputStream out = new FileOutputStream(reallyPath + "\\" + reallyName);
          byte[] buffer = new byte[1024];
          int len = 0;
          while((len = in.read(buffer)) > 0) {
            out.write(buffer, 0, len);
          }
          out.close();
          in.close();
        }
      }
      System.out.println("处理完毕...");
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
  }
  /**
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
   */
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doGet(request, response);
  }
  //随机产生唯一的文件名
  private String createFileName(String fileName) throws NoSuchAlgorithmException, UnsupportedEncodingException {
    String extension = fileName.substring(fileName.lastIndexOf("."));
    MessageDigest md = MessageDigest.getInstance("md5");
    String currentTime = System.currentTimeMillis() + "";
    return UUID.randomUUID() + currentTime + extension;
  }
  //根据哈希值产生目录
  private String mkDir(String fileName, String uploadPath) {
    int hasCode = fileName.hashCode();
    //低四位作为一级目录
    int parentDir = hasCode & 0xf;
    //二级目录
    int childDir = hasCode & 0xff >> 2;
    File file = new File(uploadPath + "\\" + parentDir + "\\" + childDir);
    if(!file.exists()) {
      file.mkdirs();
    }
    uploadPath = uploadPath + "\\" + parentDir + "\\" + childDir;
    return uploadPath;
  }
}

<%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
  <fmt:setBundle basename="pers.msidolphin.uploadservlet.lang.locale" var="bundle" scope="page"/>
  <form action="<c:url value="/UploadServlet"/>" method="post" enctype="multipart/form-data">
    <fmt:message key="username" bundle="${bundle}"/><input type="text" name="username"/>
    <br/>
    <br/>
    <fmt:message key="file1" bundle="${bundle}"/><input type="file" name="file1"/>
    <br/>
    <br/>
    <fmt:message key="file2" bundle="${bundle}"/><input type="file" name="file2"/>
    <br/>
    <br/>
    <input type="submit" value="<fmt:message key="submit" bundle="${bundle}"/>"/> 
  </form>
</body>
</html>

//设置内存缓冲区的大小，默认为10K，当上传文件大小大于缓冲区大小，fileupload组件将使用临时文件缓存上传文件
public void setSizeThreshold(int sizeThreshold);
//指定临时文件目录 默认值为System.getProperty("java.io.tmpdir")
public void setRepository(java.io.file respository); 
//构造方法
public DiskFileItemFactory(int sizeThreshold, java.io.file respository);

//判断上传表单是否为multipart/form-data类型
boolean isMultipartContent(HttpServletRequest request);
//解析request对象，并把表单中的每一个输入项包装成一个fileitem对象，返回这些对象的list集合
List<FileItem> parseRequest(HttpServletRequest request);
//设置上传文件总量的最大值 单位：字节
void setSizeMax(long sizeMax);
//设置单个上传文件的最大值 单位：字节
void setFileSizeMax(long fileSizeMax);
//设置编码格式，用于解决上传文件名的乱码问题
void setHeaderEncoding(String encoding);
//设置文件上传监听器，作用是实时获取已上传文件的大小
void setProgressListener(ProgressListener pListener);

//判断表单输入项是否为普通输入项（非文件输入项，如果是普通输入项返回true
boolean isFormField();
//获取输入项名称
String getFieldName();
//获得输入项的值
String getString();
String getString(String encoding); //可以设置编码，用于解决数据乱码问题
以下是针对非普通字段的：
//获取完整文件名（不同的浏览器可能会有所不同，有的可能包含路径，有的可能只有文件名）
String getName();
//获取文件输入流
InputStream getInputStream();