JSP 檔案上傳 JavaBean 實作教學 (簡易版)

原理說明

HTTP 檔案上傳採用 multipart/form-data 編碼，伺服器需解析請求輸入流，分離表單欄位與檔案內容。本範例示範手動解析流程，教學用途為主，生產環境建議使用成熟庫 (Apache Commons FileUpload、Servlet 3.0 @MultipartConfig)。

完整 JavaBean 原始碼

package yuanyifileup;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.PageContext;

public class yuanyifileup {
    private ServletRequest request;
    private ServletResponse response;
    private ServletConfig config;
    ServletInputStream DATA;
    int FormSize;
    File f1;
    FileOutputStream os;
    DataInputStream is;
    String filename;
    byte[] b;
    byte t;
    boolean flag = false;

    public yuanyifileup() {}

    // 以 ServletConfig 初始化
    public void initialize(ServletConfig config, HttpServletRequest request, HttpServletResponse response) throws IOException {
        this.request = request;
        this.response = response;
        this.config = config;
        DATA = request.getInputStream();
        FormSize = request.getContentLength();
    }

    // 以 PageContext 初始化 (JSP 中較方便)
    public void initialize(PageContext pageContext) throws IOException {
        request = pageContext.getRequest();
        response = pageContext.getResponse();
        config = pageContext.getServletConfig();
        DATA = request.getInputStream();
        FormSize = request.getContentLength();
    }

    // 設定儲存檔案路徑
    public boolean setFilename(String s) {
        try {
            f1 = new File(s);
            os = new FileOutputStream(f1);
        } catch(IOException e) { return false; }
        return true;
    }

    // 讀取完整請求內容至 byte 陣列
    public void getByte() {
        int i = 0;
        try {
            is = new DataInputStream(DATA);
            b = new byte[FormSize];
            while (true) {
                try {
                    t = is.readByte();
                    b[i] = t;
                    i++;
                } catch(EOFException e) { break; }
            }
            is.close();
        } catch(IOException e) {}
    }

    // 解析 multipart 資料並儲存檔案
    public boolean save() {
        int i = 0, start1 = 0, start2 = 0;
        String temp = "";
        if (!flag) { getByte(); flag = true; }
        try {
            temp = new String(b, "ISO8859_1");
        } catch(UnsupportedEncodingException e) { return false; }
        start1 = temp.indexOf("image/");
        temp = temp.substring(start1);
        start1 = temp.indexOf("\r\n\r\n");
        temp = temp.substring(start1 + 4);
        start2 = temp.indexOf("\r\n");
        if (start2 != -1) temp = temp.substring(0, start2);
        try {
            byte[] img = temp.getBytes("ISO8859_1");
            for (i = 0; i < img.length; i++) { os.write(img[i]); }
            os.close();
        } catch(IOException e) { return false; }
        return true;
    }
}

JSP 頁面呼叫範例

<%@ page import="yuanyifileup.*" %>
<%
    yuanyifileup up = new yuanyifileup();
    up.initialize(pageContext);
    if (up.setFilename("D:/upload/test.jpg")) {
        if (up.save()) out.println("上傳成功");
        else out.println("上傳失敗: " + up.getErrorMessage());
    }
%>

局限性與改進方向

• 僅支援單一檔案上傳，且硬編碼尋找 image/ 開頭，通用性差。
• 未處理檔案名稱編碼、大檔案記憶體溢位、暫存檔清理等問題。
• 現代專案請直接使用 <form method="post" enctype="multipart/form-data"> 搭配 Servlet 3.0 request.getPart() 或 Commons FileUpload。