JSP精選實用範例(三):檔案下載

要被下載的檔案先寫入到一個特定的目錄下如/WEB-INF/export，然後呼叫download.jsp?file=targetFileName取得，下載後並將檔案刪除。
程式碼:
download.jsp


<%@ page import= "java.io.*" %>

<%!

     private static final int BUFSIZE = 2048;

	  /**

     *  Sends a file to the ServletResponse output stream.  Typically

     *  you want the browser to receive a different name than the

     *  name the file has been saved in your local database, since

     *  your local names need to be unique.

     *

     *  @param request The request

     *  @param response The response

     *  @param filename The name of the file you want to download.

     *  @param original_filename The name the browser should receive.

     */

    private void doDownload( HttpServletRequest request, HttpServletResponse response,

                             String filename, String original_filename )

        throws IOException

    {

        File                f        = new File(filename);

        int                 length   = 0;

        ServletOutputStream op       = response.getOutputStream();

        ServletContext      context  = getServletConfig().getServletContext();

        String              mimetype = context.getMimeType( filename );



        //

        //  Set the response and go!

        //

        //

        response.setContentType( (mimetype != null) ? mimetype : "application/octet-stream" );

        response.setContentLength( (int)f.length() );

        response.setHeader( "Content-Disposition", "attachment; filename=\"" + original_filename + "\"" );



        //

        //  Stream to the requester.

        //

        byte[] bbuf = new byte[BUFSIZE];

        DataInputStream in = new DataInputStream(new FileInputStream(f));



        while ((in != null) && ((length = in.read(bbuf)) != -1))

        {

            op.write(bbuf,0,length);

        }



        in.close();

        op.flush();

        op.close();

    }

%>

<%

	String original_filename = request.getParameter("file");

    // Security Isuue: User can type file=../WEB-INF/web.xml

    //String filename = application.getRealPath(original_filename);

    boolean error = false;

    if (original_filename != null && !"".equals(original_filename) && !original_filename.startsWith("../")) {

    	String filename = application.getRealPath("/")+"WEB-INF/export/" + original_filename;

    	File file = new File(filename);	

    	if (file.exists()) {

    	    doDownload(request, response, filename, original_filename);

    	    // delete the file after download

    	    boolean deleted = file.delete();

    	    System.out.println("File " + original_filename + " deleted: " + deleted);

    	} else {

    		error = true;

    	}

    } else {

    	error = true;

    }

    if (error) {

    	response.setContentType("text/html; charset=UTF-8");

		out.println("File not found: " + original_filename);

    }

%>

參考資料：
http://www.jspwiki.org/wiki/MakingADownloadServlet

檔案名稱 download.jsp

描述檔案下載程式

檔案大小 3 Kbytes

下載次數 186 次

[Disk] 下載

我有在WEB-INF/export建立一個資料夾

但是好像找不到檔案

出現"File not found: null"

是怎麼回事?

lionsgogo您好：
您應該是直接打download.jsp這樣子去執行吧？正確的使用方式是需要提供一個參數file來指定要下載的檔案名稱（位於WEB-INF/export目錄下)，例如：download.jsp?file=test.csv

andowson您好
這範例程式如果下載中文檔名的檔案會有問題,自己試了一些方法,還是不成功
請問您有辦法可以讓他下載中文檔名的檔案嗎

mylipton您好:
要下載中文檔名的檔案也很簡單，只要將傳數的參數加以轉換編碼即可。


<%@ page import= "java.io.*" %>

<%!

     private static final int BUFSIZE = 2048;

	  /**

     *  Sends a file to the ServletResponse output stream.  Typically

     *  you want the browser to receive a different name than the

     *  name the file has been saved in your local database, since

     *  your local names need to be unique.

     *

     *  @param request The request

     *  @param response The response

     *  @param filename The name of the file you want to download.

     *  @param original_filename The name the browser should receive.

     */

    private void doDownload( HttpServletRequest request, HttpServletResponse response,

                             String filename, String original_filename )

        throws IOException

    {

        File                f        = new File(filename);

        int                 length   = 0;

        ServletOutputStream op       = response.getOutputStream();

        ServletContext      context  = getServletConfig().getServletContext();

        String              mimetype = context.getMimeType( filename );



        //

        //  Set the response and go!

        //

        //

        response.setContentType( (mimetype != null) ? mimetype : "application/octet-stream" );

        response.setContentLength( (int)f.length() );

        response.setHeader( "Content-Disposition", "attachment; filename=\"" + original_filename + "\"" );



        //

        //  Stream to the requester.

        //

        byte[] bbuf = new byte[BUFSIZE];

        DataInputStream in = new DataInputStream(new FileInputStream(f));



        while ((in != null) && ((length = in.read(bbuf)) != -1))

        {

            op.write(bbuf,0,length);

        }



        in.close();

        op.flush();

        op.close();

    }

%>

<%

	String original_filename = request.getParameter("file");

    String target_filename = ""; 



    // Security Isuue: User can type file=../WEB-INF/web.xml

    //String filename = application.getRealPath(original_filename);

    boolean error = false;

    if (original_filename != null && !"".equals(original_filename.trim()) && !original_filename.startsWith("../")) {

    	target_filename = new String(original_filename.getBytes("ISO-8859-1"), "MS950");

    	String filename = application.getRealPath("/")+"WEB-INF/export/" + target_filename;

    	File file = new File(filename);	

    	if (file.exists()) {

    	    doDownload(request, response, filename, original_filename);

    	    // delete the file after download

    	    //boolean deleted = file.delete();

    	    //System.out.println("File " + target_filename + " deleted: " + deleted);

    	} else {

    		error = true;

    	}

    } else {

    	error = true;

    }

    if (error) {

    	response.setContentType("text/html; charset=MS950");

		out.println("File not found: " + target_filename);

    }

%>

檔案名稱 download.jsp

描述支援中文檔名下載

檔案大小 3 Kbytes

下載次數 36 次

[Disk] 下載

andowson您好
我試過你放的程式了,還是會因為中文變亂碼的問題而找不到檔案
我也試過一些編碼的設定
也是無法成功

andowson 您好
我把ISO-88591-1 後面的UTF-8 改成big5之後可以下載中文檔名的檔案了,
但很奇怪,如果我把路徑"/WEB-INF/export" 改成別的路徑,就又會出現File not found

mylipton您好：
我今天測試了一下，發現不同的瀏覽器對於中文檔名直接輸入在網址列的處理有點不同，Google Chrome會自動把中文字改為UTF-8編碼，IE和Firefox則不會。
以下是我的測試方法，供您參考：
1.在WEB-INF/export目錄下手動產生一個文字檔，名稱就叫做「新增文字文件.txt」
2.在網址列上直接輸入：
http://localhost:8080/examples/download.jsp?file=新增文字文件.txt
修改後的程式碼如下：


<%@ page import= "java.io.*" %>

<%!

     private static final int BUFSIZE = 2048;

	  /**

     *  Sends a file to the ServletResponse output stream.  Typically

     *  you want the browser to receive a different name than the

     *  name the file has been saved in your local database, since

     *  your local names need to be unique.

     *

     *  @param request The request

     *  @param response The response

     *  @param filename The name of the file you want to download.

     *  @param original_filename The name the browser should receive.

     */

    private void doDownload( HttpServletRequest request, HttpServletResponse response,

                             String filename, String original_filename )

        throws IOException

    {

        File                f        = new File(filename);

        int                 length   = 0;

        ServletOutputStream op       = response.getOutputStream();

        ServletContext      context  = getServletConfig().getServletContext();

        String              mimetype = context.getMimeType( filename );



        //

        //  Set the response and go!

        //

        //

        response.setContentType( (mimetype != null) ? mimetype : "application/octet-stream" );

        response.setContentLength( (int)f.length() );

        response.setHeader( "Content-Disposition", "attachment; filename=\"" + original_filename + "\"" );



        //

        //  Stream to the requester.

        //

        byte[] bbuf = new byte[BUFSIZE];

        DataInputStream in = new DataInputStream(new FileInputStream(f));



        while ((in != null) && ((length = in.read(bbuf)) != -1))

        {

            op.write(bbuf,0,length);

        }



        in.close();

        op.flush();

        op.close();

    }

%>

<%

	String original_filename = request.getParameter("file");

    String target_filename = "";

    

    // Chrome will auto escape the URL characters

    String userAgent = request.getHeader("user-agent");

    System.out.println(userAgent);

    String charset = "MS950";

    if (userAgent.indexOf("Chrome") != -1) {

    	charset = "UTF-8";

    }



    // Security Isuue: User can type file=../WEB-INF/web.xml

    //String filename = application.getRealPath(original_filename);

    boolean error = false;

    if (original_filename != null && !"".equals(original_filename.trim()) && !original_filename.startsWith("../")) {

    	target_filename = new String(original_filename.getBytes("ISO-8859-1"), charset);

    	String filename = application.getRealPath("/")+"WEB-INF/export/" + target_filename;

    	File file = new File(filename);	

    	if (file.exists()) {

    	    doDownload(request, response, filename, original_filename);

    	    // delete the file after download

    	    //boolean deleted = file.delete();

    	    //System.out.println("File " + target_filename + " deleted: " + deleted);

    	} else {

    		error = true;

    	}

    } else {

    	error = true;

    }

    if (error) {

    	response.setContentType("text/html; charset=UTF-8");

		out.println("File not found: " + target_filename);

    }

%>

檔案名稱 download.jsp

描述修正後的檔案下載程式

檔案大小 3 Kbytes

下載次數 35 次

[Disk] 下載

mylipton wrote:andowson 您好
我把ISO-88591-1 後面的UTF-8 改成big5之後可以下載中文檔名的檔案了,
但很奇怪,如果我把路徑"/WEB-INF/export" 改成別的路徑,就又會出現File not found

這是設計上的問題，這個下載程式為了安全起見，將所要要下載的檔案都放在WEB-INF/export目錄下，您可以配合需要更改設計。例如您可以改為將檔案都放在WEB-INF/download目錄下，則程式中就應改為WEB-INF/download。

andowson
感謝你的回答,之前的問題已經解決了
但想請問一下,如果我想把上傳檔案傳到別的槽的資料夾改怎麼作
比如我的網站是放在C槽,但傳上來的檔案我想放到D槽

要避免發生java.lang.IllegalStateException: getOutputStream() has already been called for this response，可以在doDownload()後面加上下面兩行
out.clear();
out = pageContext.pushBody();
修改後的原始程式碼如下：
download.jsp


<%@ page import="java.io.*"%>

<%!

    private static final int BUFSIZE = 2048;

    /**

     *  Sends a file to the ServletResponse output stream.  Typically

     *  you want the browser to receive a different name than the

     *  name the file has been saved in your local database, since

     *  your local names need to be unique.

     *

     *  @param request The request

     *  @param response The response

     *  @param filename The name of the file you want to download.

     *  @param original_filename The name the browser should receive.

     */

    private void doDownload( HttpServletRequest request, HttpServletResponse response,

                             String filename, String original_filename )

        throws IOException

    {

        File                f        = new File(filename);

        int                 length   = 0;

        ServletOutputStream op       = response.getOutputStream();

        ServletContext      context  = getServletConfig().getServletContext();

        String              mimetype = context.getMimeType( filename );



        //

        //  Set the response and go!

        //

        //

        response.setContentType( (mimetype != null) ? mimetype : "application/octet-stream" );

        response.setContentLength( (int)f.length() );

        response.setHeader( "Content-Disposition", "attachment; filename=\"" + original_filename + "\"" );



        //

        //  Stream to the requester.

        //

        byte[] bbuf = new byte[BUFSIZE];

        DataInputStream in = new DataInputStream(new FileInputStream(f));



        while ((in != null) && ((length = in.read(bbuf)) != -1))

        {

            op.write(bbuf,0,length);

        }



        in.close();

        op.flush();

        op.close();

    }

%>

<%

    String original_filename = request.getParameter("file");

    String target_filename = "";

    

    // Chrome will auto escape the URL characters

    String userAgent = request.getHeader("user-agent");

    System.out.println(userAgent);

    String charset = "MS950";

    if (userAgent.indexOf("Chrome") != -1) {

    	charset = "UTF-8";

    }



    // Security Isuue: User can type file=../WEB-INF/web.xml

    //String filename = application.getRealPath(original_filename);

    boolean error = true;

    if (original_filename != null && !"".equals(original_filename.trim()) && !original_filename.startsWith("../")) {

    	target_filename = new String(original_filename.getBytes("ISO-8859-1"), charset);

    	String filename = application.getRealPath("/")+"WEB-INF/export/" + target_filename;

    	File file = new File(filename);	

    	if (file.exists()) {

    	    doDownload(request, response, filename, original_filename);

    	    // aviod java.lang.IllegalStateException: getOutputStream() has already been called for this response

    	    out.clear();

            out = pageContext.pushBody();

    	    // delete the file after download

    	    //boolean deleted = file.delete();

    	    //System.out.println("File " + target_filename + " deleted: " + deleted);

    	    error = false;

    	} 

    } 

    if (error) {

    	response.setContentType("text/html; charset=UTF-8");

    	out.println("File not found: " + target_filename);

    }

%>

檔案名稱 download.jsp

描述避免產生java.lang.IllegalStateException: getOutputStream() has already been called for this response

檔案大小 3 Kbytes

下載次數 92 次

[Disk] 下載

檔案名稱	download.jsp
描述	檔案下載程式
檔案大小	3 Kbytes
下載次數	186 次
下載