发布于 2017-11-19 19:24:20 | 44 次阅读 | 评论: 0 | 来源: 网友投递

这里有新鲜出炉的Java函数式编程,程序狗速度看过来!

Java程序设计语言

java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言,是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台(即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se))的总称。


这篇文章主要介绍了JavaWeb中的文件上传和下载功能的实现,文件上传和下载功能是非常常用的功能,需要的朋友可以参考下

在Web应用系统开发中,文件上传和下载功能是非常常用的功能,今天来讲一下JavaWeb中的文件上传和下载功能的实现。

1. 上传简单示例

Jsp


<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>文件上传下载</title>
</head>
<body>

<form action="${pageContext.request.contextPath}/UploadServlet" enctype="multipart/form-data" method="post">
 上传用户:<input type="text" name="username" /> <br />
 上传文件1:<input type="file" name="file1" /> <br />
 上传文件2:<input type="file" name="file2" /> <br />
 <input type="submit" value="上传 "/>
</form> 

<br />
${requestScope.message}

</body>
</html>

Servlet


public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 try{
 
 //1.得到解析器工厂
 DiskFileItemFactory factory = new DiskFileItemFactory();
 
 //2.得到解析器
 ServletFileUpload upload = new ServletFileUpload(factory);
 
 //3.判断上传表单的类型
 if(!upload.isMultipartContent(request)){
 //上传表单为普通表单,则按照传统方式获取数据即可
 return;
 }
 
 //为上传表单,则调用解析器解析上传数据
 List<FileItem> list = upload.parseRequest(request); //FileItem
 
 //遍历list,得到用于封装第一个上传输入项数据fileItem对象
 for(FileItem item : list){
 
 if(item.isFormField()){
 //得到的是普通输入项
 String name = item.getFieldName(); //得到输入项的名称
 String value = item.getString();
 System.out.println(name + "=" + value);
 }else{
 //得到上传输入项
 String filename = item.getName(); //得到上传文件名 C:\Documents and Settings\ThinkPad\桌面\1.txt
 filename = filename.substring(filename.lastIndexOf("\\")+1);
 InputStream in = item.getInputStream(); //得到上传数据
 int len = 0;
 byte buffer[]= new byte[1024];
 
 //用于保存上传文件的目录应该禁止外界直接访问
 String savepath = this.getServletContext().getRealPath("/WEB-INF/upload");
 System.out.println(savepath);
 
 FileOutputStream out = new FileOutputStream(savepath + "/" + filename); //向upload目录中写入文件
 while((len=in.read(buffer))>0){
 out.write(buffer, 0, len);
 }
  
 in.close();
 out.close();
 request.setAttribute("message", "上传成功");
 }
 }
 
 
 
 
 }catch (Exception e) {
 request.setAttribute("message", "上传失败");
 e.printStackTrace();
 }

 
 }

2. 修改后的上传功能:

注意事项:

1、上传文件名的中文乱码和上传数据的中文乱码
 upload.setHeaderEncoding("UTF-8");  //解决上传文件名的中文乱码
 //表单为文件上传,设置request编码无效,只能手工转换
 1.1 value = new String(value.getBytes("iso8859-1"),"UTF-8");
 1.2 String value = item.getString("UTF-8"); 

2.为保证服务器安全,上传文件应该放在外界无法直接访问的目录

3、为防止文件覆盖的现象发生,要为上传文件产生一个唯一的文件名

4、为防止一个目录下面出现太多文件,要使用hash算法打散存储

5.要限制上传文件的最大值,可以通过:ServletFileUpload.setFileSizeMax(1024)方法实现,并通过捕获:
 FileUploadBase.FileSizeLimitExceededException异常以给用户友好提示

6.想确保临时文件被删除,一定要在处理完上传文件后,调用item.delete方法

7.要限止上传文件的类型:在收到上传文件名时,判断后缀名是否合法

8、监听文件上传进度:


 ServletFileUpload upload = new ServletFileUpload(factory);
 upload.setProgressListener(new ProgressListener(){
 public void update(long pBytesRead, long pContentLength, int arg2) {
  System.out.println("文件大小为:" + pContentLength + ",当前已处理:" + pBytesRead);
 }
 });
 

9. 在web页面中动态添加文件上传输入项


 function addinput(){
  var div = document.getElementById("file");
  
  var input = document.createElement("input");
  input.type="file";
  input.name="filename";
  
  var del = document.createElement("input");
  del.type="button";
  del.value="删除";
  del.onclick = function d(){
  this.parentNode.parentNode.removeChild(this.parentNode);
  }
  
  
  var innerdiv = document.createElement("div");
  
  
  innerdiv.appendChild(input);
  innerdiv.appendChild(del);
  
  div.appendChild(innerdiv);
  }

上传jsp:


<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
 <title>My JSP 'upload2.jsp' starting page</title>
 
 <script type="text/javascript">
  function addinput(){
  var div = document.getElementById("file");
  
  var input = document.createElement("input");
  input.type="file";
  input.name="filename";
  
  var del = document.createElement("input");
  del.type="button";
  del.value="删除";
  del.onclick = function d(){
  this.parentNode.parentNode.removeChild(this.parentNode);
  }
  
  
  var innerdiv = document.createElement("div");
  
  
  innerdiv.appendChild(input);
  innerdiv.appendChild(del);
  
  div.appendChild(innerdiv);
  }
 </script>
 
 </head>
 
 <body>
 
 
 <form action="" enctype="mutlipart/form-data"></form>
 <table>
  <tr>
  <td>上传用户:</td>
  <td><input type="text" name="username"></td>
  </tr>
 <tr>  
  <td>上传文件:</td>
  <td>
  <input type="button" value="添加上传文件" onclick="addinput()">
  </td>
  </tr>
  <tr>
  <td></td>
  <td>
  <div id="file">
  
  </div>
  </td>
  </tr>
  
 </table>
 
 
 </body>
</html>

上传servlet


public class UploadServlet1 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 //request.getParameter("username"); //****错误
 request.setCharacterEncoding("UTF-8"); //表单为文件上传,设置request编码无效
 
 //得到上传文件的保存目录
 String savePath = this.getServletContext().getRealPath("/WEB-INF/upload");
 
 try{
 DiskFileItemFactory factory = new DiskFileItemFactory();
 factory.setRepository(new File(this.getServletContext().getRealPath("/WEB-INF/temp")));
 
 ServletFileUpload upload = new ServletFileUpload(factory);
 /*upload.setProgressListener(new ProgressListener(){
 public void update(long pBytesRead, long pContentLength, int arg2) {
  System.out.println("文件大小为:" + pContentLength + ",当前已处理:" + pBytesRead);
 }
 });*/
 
 upload.setHeaderEncoding("UTF-8"); //解决上传文件名的中文乱码
 
 if(!upload.isMultipartContent(request)){
 //按照传统方式获取数据
 return;
 }
 
 
 /*upload.setFileSizeMax(1024);
 upload.setSizeMax(1024*10);*/
 List<FileItem> list = upload.parseRequest(request);
 for(FileItem item : list){
 
 if(item.isFormField()){
  //fileitem中封装的是普通输入项的数据
  String name = item.getFieldName();
  String value = item.getString("UTF-8");
  //value = new String(value.getBytes("iso8859-1"),"UTF-8");
  System.out.println(name + "=" + value);
 }else{
  //fileitem中封装的是上传文件
  String filename = item.getName(); //不同的浏览器提交的文件是不一样 c:\a\b\1.txt 1.txt
  System.out.println(filename);
  if(filename==null || filename.trim().equals("")){
  continue;
  }
  filename = filename.substring(filename.lastIndexOf("\\")+1);
  
  InputStream in = item.getInputStream();
  String saveFilename = makeFileName(filename); //得到文件保存的名称
  
  String realSavePath = makePath(saveFilename, savePath); //得到文件的保存目录
  FileOutputStream out = new FileOutputStream(realSavePath + "\\" + saveFilename);
  byte buffer[] = new byte[1024];
  int len = 0;
  while((len=in.read(buffer))>0){
  out.write(buffer, 0, len);
  }
  
  in.close();
  out.close();
  item.delete(); //删除临时文件
  
 }
 
 }
 
 }catch (FileUploadBase.FileSizeLimitExceededException e) {
 e.printStackTrace();
 request.setAttribute("message", "文件超出最大值!!!");
 request.getRequestDispatcher("/message.jsp").forward(request, response);
 return;
 }
 catch (Exception e) {
 e.printStackTrace();
 }
 }
 
 public String makeFileName(String filename){ //2.jpg
 return UUID.randomUUID().toString() + "_" + filename;
 }
 
 public String makePath(String filename,String savePath){
 
 int hashcode = filename.hashCode();
 int dir1 = hashcode&0xf; //0--15
 int dir2 = (hashcode&0xf0)>>4; //0-15
 
 String dir = savePath + "\\" + dir1 + "\\" + dir2; //upload\2\3 upload\3\5
 File file = new File(dir);
 if(!file.exists()){
 file.mkdirs();
 }
 return dir;
 }

 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doGet(request, response);
 }

}

3. 下载功能


//列出网站所有下载文件
public class ListFileServlet extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 
 String filepath = this.getServletContext().getRealPath("/WEB-INF/upload");
 Map map = new HashMap();
 listfile(new File(filepath),map);
 
 request.setAttribute("map", map);
 request.getRequestDispatcher("/listfile.jsp").forward(request, response);
 }
 
 public void listfile(File file,Map map){

 if(!file.isFile()){
 File files[] = file.listFiles();
 for(File f : files){
 listfile(f,map);
 }
 }else{
 String realname = file.getName().substring(file.getName().indexOf("_")+1); //9349249849-88343-8344_阿_凡_达.avi
 map.put(file.getName(), realname);
 }
 
 }
 
 

 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doGet(request, response);
 }

}

jsp显示


<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
 <title>My JSP 'listfile.jsp' starting page</title>
 </head>
 
 <body>

 <c:forEach var="me" items="${map}">
  <c:url value="/servlet/DownLoadServlet" var="downurl">
  <c:param name="filename" value="${me.key}"></c:param>
  </c:url>
  ${me.value } <a href="${downurl}">下载</a> <br/>
 </c:forEach>
 
 </body>
</html>

下载处理servlet


public class DownLoadServlet extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 
 
 String filename = request.getParameter("filename"); //23239283-92489-阿凡达.avi
 filename = new String(filename.getBytes("iso8859-1"),"UTF-8");
 String path = makePath(filename,this.getServletContext().getRealPath("/WEB-INF/upload"));
 
 File file = new File(path + "\\" + filename);
 if(!file.exists()){
 request.setAttribute("message", "您要下载的资源已被删除!!");
 request.getRequestDispatcher("/message.jsp").forward(request, response);
 return;
 }
 
 String realname = filename.substring(filename.indexOf("_")+1);
 response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8"));
 
 FileInputStream in = new FileInputStream(path + "\\" + filename);
 OutputStream out = response.getOutputStream();
 byte buffer[] = new byte[1024];
 int len = 0;
 while((len=in.read(buffer))>0){
 out.write(buffer, 0, len);
 }
 in.close();
 out.close();
 }
 
 
 public String makePath(String filename,String savePath){
 
 int hashcode = filename.hashCode();
 int dir1 = hashcode&0xf; //0--15
 int dir2 = (hashcode&0xf0)>>4; //0-15
 
 String dir = savePath + "\\" + dir1 + "\\" + dir2; //upload\2\3 upload\3\5
 File file = new File(dir);
 if(!file.exists()){
 file.mkdirs();
 }
 return dir;
 }


 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doGet(request, response);
 }

}

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持PHPERZ。



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