依赖2个jar包：commons-fileupload，commons-io。

代码如下：

    package com.example.web;                import java.io.File;        import java.io.FileOutputStream;        import java.io.IOException;        import java.io.InputStream;        import java.io.OutputStream;        import java.io.PrintWriter;        import java.text.DateFormat;        import java.text.SimpleDateFormat;        import java.util.Date;        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.FileUploadException;        import org.apache.commons.fileupload.disk.DiskFileItemFactory;        import org.apache.commons.fileupload.servlet.ServletFileUpload;        import org.apache.commons.io.IOUtils;                public class FileUpload extends HttpServlet {                    public void doGet(HttpServletRequest request, HttpServletResponse response)                    throws ServletException, IOException {                                request.setCharacterEncoding("UTF-8");                response.setContentType("text/html;charset=utf-8");                PrintWriter out=response.getWriter();                //指定文件存放目录                String storePath=getServletContext().getRealPath("WEB-INF/files");                File file=new File(storePath);                //如果目录不存在，需要创建                if(!file.exists()){                    file.mkdirs();                }                //要检查是不是enctype=multipart/form-data提交过来的数据                boolean isMultipart=ServletFileUpload.isMultipartContent(request);                //如果不是，需要处理                if(!isMultipart){                    out.write("请将enctype设置成multipart/form-data类型");                    response.setHeader("Refresh", "1;URL="+request.getContextPath());                    return;                }                //去生成一个文件上传的FileUpload对象                DiskFileItemFactory factory=new DiskFileItemFactory();                //设置一个临时目录                //factory.setRepository(new File("E:/temp"));temp文件需要临时创建，我已经删掉了                                ServletFileUpload upload=new ServletFileUpload(factory);                //将用户的请求转化为List<FileItem>                try {                    List<FileItem> items=upload.parseRequest(request);                    //遍历List<FileItem>中的数据                    for (FileItem item : items) {                        //如果部分文件没有上传                        if("".equals(item.getName())){                            continue;                        }                        //判断是普通字段                        if(item.isFormField()){                            String fieldName=item.getFieldName();                            String fieldValue=item.getString("UTF-8");                            System.out.println(fieldName+":"+fieldValue);                        }else{                            //是上传的文件                            //需要获取文件名,有可能是路径                            String fileName=item.getName();                            fileName=fileName.substring(fileName.lastIndexOf(File.separator)+1);                            //文件名同名问题                            fileName=UUID.randomUUID().toString()+"_"+fileName;                            //解决一个文件夹下的文件过多的问题                            //用时间来生成子目录                            //String childPath=generateDir(storePath);                            //用hashcode来生成子目录                            String childPath=generateDir(storePath,fileName);                            //获取上传文件的数据                            InputStream is=item.getInputStream();                            OutputStream os=new FileOutputStream(storePath+File.separator+childPath+File.separator+fileName);                            IOUtils.copy(is, os);                            os.close();                            is.close();                            //item.delete();//清空临时文件                        }                    }                    out.write("文件上传成功<a href='"+request.getContextPath()+"'>继续上传</a>");                } catch (FileUploadException e) {                    e.printStackTrace();                }            }                            private String generateDir(String storePath, String fileName) {                int hashcode=fileName.hashCode();                int dir1=hashcode &  0xf;                int dir2=(hashcode & 0xf0)>>4;                String childPath=dir1+File.separator+dir2;                File file=new File(storePath,childPath);                if(!file.exists()){                    file.mkdirs();                }                return childPath;            }                            private String generateDir(String storePath) {                DateFormat df=new SimpleDateFormat("yyyyMMddhhmmss");                String childPath=df.format(new Date());                File file=new File(storePath, childPath);                if(!file.exists()){                    file.mkdirs();                }                return childPath;            }                            public void doPost(HttpServletRequest request, HttpServletResponse response)                    throws ServletException, IOException {                this.doGet(request, response);                    }                }