Jsp/Servlet:实现文件上传与下载

This doc shows how to upload and download files with Jsp& Servlet technology.

author: ZJ 07-3-7

Blog: [url]http://zhangjunhd.blog.51cto.com/[/url]

1 ．客户端上传文件

客户端通过一个 Jsp 页面，上传文件到服务器，该 Jsp 页面必须含有 File 类表单，并且表单必须设置 enctype="multipart/form-data" 。提交表单时通过内置对象 request ， request.getInputStream(); 方法获得一个输入流。

在上传文件时，会有附加信息，如下所示：

-----------------------------7d 71042a 40328 Content-Disposition: form-data; name="fileforload"; filename="C:\Documents and Settings\ZJ\ 桌面 \book.txt" Content-Type: text/plain // 此处为文件内容 -----------------------------7d 71042a 40328 Content-Disposition: form-data; name="submit"   commit -----------------------------7d 71042a 40328--

附加信息大小为 297 字节（不确定这个值，测试得到），可通过 request.getContentLength()>297 来判断是否上传了文件还是提交空字符串。

2 ．测试

fileupload.jsp 负责提交文件， accept.jsp 负责实现上传功能。

fileupload.jsp

< html > < head >   < meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" >   < title > This page for FileUpload </ title > </ head > < body >   < p > Choose the file for uploading:   < form action = "accept.jsp" method = post enctype = "multipart/form-data" >     < input type = file name = fileforload size = 30 >     < br >     < input type = submit value = commit name = submit >   </ form > </ body > </ html >

 

accept.jsp

< html > < head > <%@ page language = "java" import = "java.io.*" %> < meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" > < title > This page for response </ title > </ head > < body >     <%     try {        if (request.getContentLength() > 297) {            InputStream in = request.getInputStream();            File f = new File( "d:/temp" , "test.txt" );            FileOutputStream o = new FileOutputStream(f);            byte b[] = new byte [1024];            int n;            while ((n = in.read(b)) != -1) {                o.write(b, 0, n);            }            o.close();            in.close();            out.print( "File upload success!" );            } else {               out.print( "No file!" );            }        } catch (IOException e) {            out.print( "upload error." );            e.printStackTrace();        }     %>     </ body > </ html >

 

服务器端得到的上传文件I like.txt ，取名为test.txt

-----------------------------7d75b1540328 Content-Disposition: form-data; name="fileforload"; filename="C:\Documents and Settings\ZJ\ 桌面 \I like.txt" Content-Type: text/plain   我喜欢驾驭着代码在风驰电掣中创造完美 ; 我喜欢操纵着代码在随心所欲中体验生活 ; 我喜欢用心情代码编制我小小的与众不同 ; 每一段新的代码在我手中延生对我来说就象观看刹那花开的感动 ; 我不需要焦点 . 因为我就是焦点 !   -----------------------------7d75b1540328 Content-Disposition: form-data; name="submit"   commit -----------------------------7d75b1540328--

3 ．去除附加信息

按照 HTTP 协议，文件表单提交的信息中，前 4 行和后 5 行是表单本身的信息，中间部分才是上传的文件的内容。下例对上传的文件进行处理，获取文件名，并去除附加信息。

4 ．测试

fileupload.jsp 不变， accept.jsp 修改如下：

< html > < head > <%@ page language = "java" import = "java.io.*" %> < meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" > < title > The real file </ title > </ head > < body > <% try {     //use sessionid to create a temp file.     String tempFileName=(String)session.getId();     //create the temp file.     File temp= new File( "d:/temp" ,tempFileName);     FileOutputStream o= new FileOutputStream(temp);     if (request.getContentLength()>297){       //write the upload content to the temp file.       InputStream in=request.getInputStream();       byte b[]= new byte [1024];       int n;       while ((n=in.read(b))!=-1){          o.write(b,0,n);       }       o.close();       in.close();       //read the temp file.       RandomAccessFile random= new RandomAccessFile(temp, "r" );       //read Line2 to find the name of the upload file.       int second=1;       String secondLine= null ;       while (second<=2){          secondLine=random.readLine();          second++;       }       //get the last location of the dir char.'\\'.       int position=secondLine.lastIndexOf( '\\' );       //get the name of the upload file.       String fileName=secondLine.substring(position+1,secondLine.length()-1);       //relocate to the head of file.       random.seek(0);       //get the location of the char.'Enter' in Line4.       long forthEndPosition=0;       int forth=1;       while ((n=random.readByte())!=-1&&(forth<=4)){          if (n== '\n' ){              forthEndPosition=random.getFilePointer();              forth++;          }       }       File realFile= new File( "d:/temp" ,fileName);       RandomAccessFile random2= new RandomAccessFile(realFile, "rw" );       //locate the end position of the content.Count backwards 6 lines.       random.seek(random.length());       long endPosition=random.getFilePointer();       long mark=endPosition;       int j=1;       while ((mark>=0)&&(j<=6)){          mark--;          random.seek(mark);          n=random.readByte();          if (n== '\n' ){              endPosition=random.getFilePointer();              j++;          }       }       //locate to the begin of content.Count for 4 lines's end position.       random.seek(forthEndPosition);       long startPoint=random.getFilePointer();       //read the real content and write it to the realFile.       while (startPoint<endPosition-1){          n=random.readByte();          random2.write(n);          startPoint=random.getFilePointer();       }       random2.close();       random.close();       //delete the temp file.       temp.delete();       out.print( "File upload success!" );     }     else {        out.print( "No file!" );     } } catch (IOException e){     out.print( "upload error." );     e.printStackTrace(); } %> </ body > </ html >

（注：如果文件名是中文，会出现乱码。）

5 ．文件下载

Jsp 内置对象 response 调用方法 getOutputStream （）可以获取一个指向客户的输出流，服务器将文件写入这个流，然后可下载此文件。

6 ．测试

    download.jsp 显示下载选项， LoadFile.java （ Servlet ）负责下载文件。

download.jsp

< html > < head >     < meta http-equiv = "Content-Type" content = "text/html; charset=GB18030" >     < title > download page </ title > </ head > < body >     < a href = loadFile > Download:test.zip </ a > </ body > </ html >

 

LoadFile.java

package com.zj.sample; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.OutputStream; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;   public class LoadFile extends HttpServlet {     public void doGet(HttpServletRequest request, HttpServletResponse response)            throws IOException, ServletException {        OutputStream o = response.getOutputStream();        byte b[] = new byte [1024];        // the file to download.        File fileLoad = new File( "d:/temp" , "test.rar" );        // the dialogbox of download file.        response.setHeader( "Content-disposition" , "attachment;filename="               + "test.rar" );        // set the MIME type.        response.setContentType( "application/x-tar" );        // get the file length.        long fileLength = fileLoad.length();        String length = String.valueOf(fileLength);        response.setHeader( "Content_Length" , length);        // download the file.        FileInputStream in = new FileInputStream(fileLoad);        int n = 0;        while ((n = in.read(b)) != -1) {            o.write(b, 0, n);        }     }       public void doPost(HttpServletRequest request, HttpServletResponse response)  throws IOException, ServletException {        doGet(request, response);     } }

 

web.xml （注册 servlet ）

< servlet >     < servlet-name > LoadFileServlet </ servlet-name >     < servlet-class > com.zj.sample.LoadFile </ servlet-class > </ servlet > < servlet-mapping >     < servlet-name > LoadFileServlet </ servlet-name >     < url-pattern > /loadFile </ url-pattern > </ servlet-mapping >