JSP 實現多檔案打包下載 (ZIP) 完整原始碼

功能需求

使用者勾選多個檔案，伺服器端即時壓縮為 ZIP 檔並提供下載，不佔用伺服器暫存空間。

核心實作類別

<%@page import="java.util.*, java.net.*, java.text.*, java.util.zip.*, java.io.*" %>
<%!
    // 遞迴展開目錄結構
    static Vector expandFileList(String[] files, boolean inclDirs) {
        Vector v = new Vector();
        if (files == null) return v;
        for (int j=0; j < files.length; j++)
            v.add(new File(URLDecoder.decode(files[j])));
        for (int i=0; i < v.size(); i++) {
            File f = (File) v.get(i);
            if (f.isDirectory()) {
                File[] fs = f.listFiles();
                for (int n=0; n < fs.length; n++) v.add(fs[n]);
                if (!inclDirs) { v.remove(i); i--; }
            }
        }
        return v;
    }

    // 將 ZIP 輸出流導向 JSP out 隱含物件
    class Writer2Stream extends OutputStream {
        Writer out;
        Writer2Stream(Writer w) { super(); out = w; }
        public void write(int i) throws IOException { out.write(i); }
        public void write(byte[] b) throws IOException {
            for (int j=0; j<b.length; j++) {
                int n = b[j];
                n = ((n>>>4)&0xF)*16 + (n&0xF);
                out.write(n);
            }
        }
        public void write(byte[] b, int off, int len) throws IOException {
            for (int j=off; j<off+len; j++) {
                int n = b[j];
                n = ((n>>>4)&0xF)*16 + (n&0xF);
                out.write(n);
            }
        }
    }
%>
<%
    ///// 下載壓縮檔包
    Vector v = expandFileList(request.getParameterValues("selfile"), false);
    if (v.size() == 0) {
        request.setAttribute("error", "No files selected");
    } else {
        File dir_file = new File(request.getRealPath("") + "/myfile/");
        int dir_l = dir_file.getAbsolutePath().length();
        response.setContentType("application/zip");
        response.setHeader("Content-Disposition", "attachment;filename=downloadname.zip");
        out.clearBuffer();
        ZipOutputStream zipout = new ZipOutputStream(new Writer2Stream(out));
        zipout.setComment("Download selected files as one ZIP file: downloadname.zip");
        zipout.setLevel(1); // 最快壓縮
        for (int i=0; i<v.size(); i++) {
            File f = (File)v.get(i);
            if (f.canRead()) {
                zipout.putNextEntry(new ZipEntry(f.getAbsolutePath().substring(dir_l+1)));
                BufferedInputStream fr = new BufferedInputStream(new FileInputStream(f));
                byte buffer[] = new byte[0xffff];
                int b;
                while ((b=fr.read()) != -1) zipout.write(b);
                fr.close();
                zipout.closeEntry();
            }
        }
        zipout.finish();
        out.flush();
    }
%>

關鍵技術點

1. 遞迴掃描目錄：expandFileList 支援資料夾遞迴，可選擇是否包含目錄本身。
2. 串流式壓縮：Writer2Stream 將 ZipOutputStream 直接寫入 JSP out，避免產生暫存檔。
3. 中文檔名編碼：實務上建議對 ZipEntry 名稱使用 UTF-8 編碼，防止下載後檔名亂碼。
4. 大檔案支援：若檔案極大，建議改用 ZipOutputStream 搭配 ServletOutputStream 並啟用 response.setBufferSize()。

前端呼叫範例

<form action="downloadZip.jsp" method="post">
    <input type="checkbox" name="selfile" value="file1.txt"> file1.txt<br>
    <input type="checkbox" name="selfile" value="dir1/"> dir1/<br>
    <input type="submit" value="打包下載">
</form>