使用jsp/servlet实现文件上传与下载

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1.实现文件上传与下载

我们需要导入两个额外的jar包，一个是common-io-2.2.jar，另一个是commons-fileupload-1.3.1.jar，将这个两个jar 包导入WEB-INF/lib目录里。

首先，想要在web端即网页上实现文件上传，必须要提供一个选择文件的框，即设置一个<input type="file"/>的元素，还需要对<input>元素外的表单form进行设置，将form的enctype属性设置为“multipart/form-data”，即<form action="" method="post" enctype="multipart/form-data">，当然请求方式也必须是post

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>            <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">      <html>        <head>          <title>文件上传</title>                    <meta http-equiv="pragma" content="no-cache">          <meta http-equiv="cache-control" content="no-cache">          <meta http-equiv="expires" content="0">          <!--         <link rel="stylesheet" type="text/css" href="styles.css">         -->              </head>                <body>          <form action="${pageContext.request.contextPath}/servlet/UploadServlet" method="post" enctype="multipart/form-data">              name:<input name="name"/><br/>              file1:<input type="file" name="f1"/><br/>                            <input type="submit" value="上传">          </form>        </body>      </html>

jsp页面做好之后，我们就要写一个UploadServlet，在编写上传servlet时，我们需要考虑到如果上传的文件出现重名的情况，以及上传的文件可能会出现的乱码情况，所以我们需要编码与客户端一致

    public class UploadServlet 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();              System.out.print(request.getRemoteAddr());              boolean isMultipart = ServletFileUpload.isMultipartContent(request);              if(!isMultipart){                  throw new RuntimeException("请检查您的表单的enctype属性，确定是multipart/form-data");              }              DiskFileItemFactory dfif = new DiskFileItemFactory();              ServletFileUpload parser = new ServletFileUpload(dfif);                            parser.setFileSizeMax(3*1024*1024);//设置单个文件上传的大小              parser.setSizeMax(6*1024*1024);//多文件上传时总大小限制                            List<FileItem> items = null;              try {                  items = parser.parseRequest(request);              }catch(FileUploadBase.FileSizeLimitExceededException e) {                  out.write("上传文件超出了3M");                  return;              }catch(FileUploadBase.SizeLimitExceededException e){                  out.write("总文件超出了6M");                  return;              }catch (FileUploadException e) {                  e.printStackTrace();                  throw new RuntimeException("解析上传内容失败，请重新试一下");              }                            //处理请求内容              if(items!=null){                  for(FileItem item:items){                      if(item.isFormField()){                          processFormField(item);                      }else{                          processUploadField(item);                      }                  }              }                            out.write("上传成功！");          }          private void processUploadField(FileItem item) {              try {                  String fileName = item.getName();                                                      //用户没有选择上传文件时                  if(fileName!=null&&!fileName.equals("")){                      fileName = UUID.randomUUID().toString()+"_"+FilenameUtils.getName(fileName);                                            //扩展名                      String extension = FilenameUtils.getExtension(fileName);                      //MIME类型                      String contentType = item.getContentType();                                                                                        //分目录存储：日期解决          //          Date now = new Date();          //          DateFormat df = new SimpleDateFormat("yyyy-MM-dd");          //                    //          String childDirectory  = df.format(now);                                                                  //按照文件名的hashCode计算存储目录                      String childDirectory = makeChildDirectory(getServletContext().getRealPath("/WEB-INF/files/"),fileName);                                            String storeDirectoryPath = getServletContext().getRealPath("/WEB-INF/files/"+childDirectory);                      File storeDirectory = new File(storeDirectoryPath);                      if(!storeDirectory.exists()){                          storeDirectory.mkdirs();                      }                      System.out.println(fileName);                      item.write(new File(storeDirectoryPath+File.separator+fileName));//删除临时文件                                        }              } catch (Exception e) {                  throw new RuntimeException("上传失败,请重试");              }                        }          //计算存放的子目录          private String makeChildDirectory(String realPath, String fileName) {              int hashCode = fileName.hashCode();              int dir1 = hashCode&0xf;// 取1~4位              int dir2 = (hashCode&0xf0)>>4;//取5~8位                            String directory = ""+dir1+File.separator+dir2;              File file = new File(realPath,directory);              if(!file.exists())                  file.mkdirs();                            return directory;          }          private void processFormField(FileItem item) {              String fieldName = item.getFieldName();//字段名              String fieldValue;              try {                  fieldValue = item.getString("UTF-8");              } catch (UnsupportedEncodingException e) {                  throw new RuntimeException("不支持UTF-8编码");              }              System.out.println(fieldName+"="+fieldValue);          }                public void doPost(HttpServletRequest request, HttpServletResponse response)                  throws ServletException, IOException {              doGet(request, response);          }            }

文件下载通过一个servlet与一个jsp页面来显示，servlet代码如下：

    public class ShowAllFilesServlet extends HttpServlet {                public void doGet(HttpServletRequest request, HttpServletResponse response)                  throws ServletException, IOException {              String storeDirectory = getServletContext().getRealPath("/WEB-INF/files");              File root = new File(storeDirectory);                            //用Map保存递归的文件名：key:UUID文件名   value:老文件名              Map<String, String> map = new HashMap<String, String>();              treeWalk(root,map);                            request.setAttribute("map", map);              request.getRequestDispatcher("/listFiles.jsp").forward(request, response);          }          //递归，把文件名放到Map中          private void treeWalk(File root, Map<String, String> map) {              if(root.isFile()){                  String fileName = root.getName();//文件名                       String oldFileName = fileName.substring(fileName.indexOf("_")+1);                  map.put(fileName, oldFileName);              }else{                  File fs[] = root.listFiles();                  for(File file:fs){                      treeWalk(file, map);                  }              }                        }                public void doPost(HttpServletRequest request, HttpServletResponse response)                  throws ServletException, IOException {              doGet(request, response);          }            }

通过上面的servlet转发到listFiles.jsp页面，listFiles.jsp页面：

    <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>      <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>      <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">      <html>        <head>          <title>title</title>                    <meta http-equiv="pragma" content="no-cache">          <meta http-equiv="cache-control" content="no-cache">          <meta http-equiv="expires" content="0">          <!--          <link rel="stylesheet" type="text/css" href="styles.css">          -->              </head>                <body>          <h1>以下资源可供下载</h1>          <c:forEach items="${map}" var="me">              <c:url value="/servlet/DownloadServlet" var="url">                  <c:param name="filename" value="${me.key}"></c:param>              </c:url>              ${me.value}  <a href="${url}">下载</a><br/>          </c:forEach>        </body>      </html>

我们再编写一个DownloadServlet public class DownloadServlet extends HttpServlet {                public void doGet(HttpServletRequest request, HttpServletResponse response)                  throws ServletException, IOException {              String uuidfilename = request.getParameter("filename");//get方式提交的              uuidfilename = new String(uuidfilename.getBytes("ISO-8859-1"),"UTF-8");//UUID的文件名                            String storeDirectory = getServletContext().getRealPath("/WEB-INF/files");              //得到存放的子目录              String childDirecotry = makeChildDirectory(storeDirectory, uuidfilename);                            //构建输入流              InputStream in = new FileInputStream(storeDirectory+File.separator+childDirecotry+File.separator+uuidfilename);              //下载              String oldfilename = uuidfilename.substring(uuidfilename.indexOf("_")+1);              //通知客户端以下载的方式打开              response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(oldfilename, "UTF-8"));                            OutputStream out = response.getOutputStream();                            int len = -1;              byte b[] = new byte[1024];              while((len=in.read(b))!=-1){                  out.write(b,0,len);              }              in.close();              out.close();                        }                public void doPost(HttpServletRequest request, HttpServletResponse response)                  throws ServletException, IOException {              doGet(request, response);          }          //计算存放的子目录          private String makeChildDirectory(String realPath, String fileName) {              int hashCode = fileName.hashCode();              int dir1 = hashCode&0xf;// 取1~4位              int dir2 = (hashCode&0xf0)>>4;//取5~8位                            String directory = ""+dir1+File.separator+dir2;              File file = new File(realPath,directory);              if(!file.exists())                  file.mkdirs();                            return directory;          }      }

完成文件上传下载

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