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

代码如下：

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            try {                List items=upload.parseRequest(request);                //遍历List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("文件上传成功继续上传");            } 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);            }        }