Jsp中實現文件上傳與下載

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．客戶端上傳文件
客戶端通過一個Jsp頁面，上傳文件到服務器，該Jsp頁面必須含有File類表單，並且表單必須設置enctype="multipart/form- data"。提交表單時通過內置對象request，request.getInputStream();方法獲得一個輸入流。
在上傳文件時，會有附加信息，如下所示：

-----------------------------7d71042a40328
Content-Disposition: form-data; name="fileforload"; filename="C:\Documents and Settings\ZJ\桌面\book.txt"
Content-Type: text/plain
//此處爲文件內容
-----------------------------7d71042a40328
Content-Disposition: form-data; name="submit"

commit
-----------------------------7d71042a40328--

附加信息大小爲297字節（不確定這個值，測試得到），可通過request.getContentLength()>297來判斷是否上傳了文件還是提交空字符串。

2．測試
fileupload.jsp負責提交文件，accept.jsp負責實現上傳功能。
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>
<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>

服務器端得到的上傳文件I like.txt，取名爲test.txt

-----------------------------7d75b1540328
Content-Disposition: form-data; name="fileforload"; filename="C:\Documents and Settings\ZJ\桌面\I like.txt"
Content-Type: text/plain

我喜歡駕馭着代碼在風馳電掣中創造完美;
我喜歡操縱着代碼在隨心所欲中體驗生活;
我喜歡用心情代碼編制我小小的與衆不同;
每一段新的代碼在我手中延生對我來說就象觀看剎那花開的感動;
我不需要焦點.因爲我就是焦點!

-----------------------------7d75b1540328
Content-Disposition: form-data; name="submit"

commit
-----------------------------7d75b1540328--

3．去除附加信息
按照HTTP協議，文件表單提交的信息中，前4行和後5行是表單本身的信息，中間部分纔是上傳的文件的內容。下例對上傳的文件進行處理，獲取文件名，並去除附加信息。

4．測試
fileupload.jsp不變，accept.jsp修改如下：

<html>
<head>
<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，會出現亂碼。）

5．文件下載
Jsp內置對象response調用方法getOutputStream（）可以獲取一個指向客戶的輸出流，服務器將文件寫入這個流，然後可下載此文件。

6．測試
download.jsp顯示下載選項，LoadFile.java（Servlet）負責下載文件。
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;

@SuppressWarnings("serial")
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",
      "p_w_upload;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（註冊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>

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