使用jsp/servlet简单实现文件上传与下载
使用JSP/Servlet简单实现文件上传与下载
通过学习黑马jsp教学视频，我学会了使用jsp与servlet简单地实现web的文件的上传与下载，首先感谢黑马。好了，下面来简单了解如何通过使用jsp与servlet实现文件上传与下载。
在写代码之前，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，光有这个还不行，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。让我们来简单做一个上传的jsp页面：
<%@ 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，并且根据文件名的hashcode计算存储目录，避免一个文件夹中的文件过多，当然为了保证服务器的安全，我们将存放文件的目录放在用户直接访问不到的地方，比如在WEB-INF文件夹下创建一个file文件夹。具体做法如下：
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);
}
}
至此，上传的任务就基本完成了，有了上传当然也要有下载功能，在下载之前，我们需要将所有已经上传的文件显示在网页上，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>
到这里，文件也显示出来了，就需要点击下载进行下载文件了，最后一步，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;
}
}
文件上传与下载就已经全部完成了。