使用fileupload包進行檔案上傳

• 檔案上傳的必要前提：
  1. 提供form表單，method必須是post
  2. form表單的enctype必須是multipart/form-data（預設是application/x-www-form-urlencoded）
  3. 提供input type="file"類的上傳輸入域
• 下面是實作檔案上傳的示例代碼：
• 需要導入的包如下：

WEB-INF/lib/commons-fileupload-1.2.2.jar
WEB-INF/lib/commons-io-2.2.jar
           

package Upload;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.List;
import java.util.UUID;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FilenameUtils;

public class UploadServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 要執行檔案上傳的操作
        // 判斷表單是否支援檔案上傳。即：enctype="multipart/form-data"
        boolean isMultipartContent = ServletFileUpload.isMultipartContent(request);
        if (!isMultipartContent) {
            throw new RuntimeException("your form is not multipart/form-data");
        }

        // 建立一個DiskFileItemfactory工廠類
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setRepository(new File("d:\\"));// 指定臨時檔案的存儲目錄
        // 建立一個ServletFileUpload核心對象
        ServletFileUpload sfu = new ServletFileUpload(factory);
        // 解決上傳檔案名亂碼問題
        sfu.setHeaderEncoding("UTF-8");

        // 解析request對象，并得到一個表單項的集合
        try {
            List<FileItem> fileItems = sfu.parseRequest(request);

            // 周遊表單項資料
            for (FileItem fileitem : fileItems) {
                if (fileitem.isFormField()) {
                    // 普通表單項
                    processFormField(fileitem);
                } else {
                    // 上傳表單項
                    processUploadField(fileitem);
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        }
    }

    // 上傳表單項
    private void processUploadField(FileItem fileitem) {
        try {
            // 得到檔案輸入流
            InputStream is = fileitem.getInputStream();

            // 建立一個檔案存盤的目錄
            String directoryRealPath = this.getServletContext().getRealPath("/WEB-INF/upload");
            File storeDirectory = new File(directoryRealPath);
            if (!storeDirectory.exists()) {
                storeDirectory.mkdirs();// 建立一個指定的目錄
            }
            // 得到上傳的檔案名稱
            String filename = fileitem.getName();
            //下面的操作隻是為了防止上面的上傳檔案名包含路徑名
            if (filename != null) {
                filename = FilenameUtils.getName(filename);
            }

            // 解決檔案同名的問題
            filename = UUID.randomUUID() + "_" + filename;

            // 目錄打散
            String childDirectory = makeChildDirectory(storeDirectory, filename);

            // 在storeDirectory下，建立完整目錄下的檔案
            File file = new File(storeDirectory, childDirectory + File.separator + filename); // 絕對目錄/生成的子目錄/檔案名
            // 通過檔案輸出流将上傳的檔案儲存到磁盤
            FileOutputStream fos = new FileOutputStream(file);

            int len = 0;
            byte[] b = new byte[1024];
            while ((len = is.read(b)) != -1) {
                fos.write(b, 0, len);
            }
            fos.close();
            is.close();
            //删除臨時檔案
            fileitem.delete();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 目錄打散
    private String makeChildDirectory(File storeDirectory, String filename) {
        int hashcode = filename.hashCode();// 傳回字元轉換的32位hashcode碼
        System.out.println(hashcode);//1417749484
        String code = Integer.toHexString(hashcode); // 把hashcode轉換為16進制的字元
        System.out.println(code);//548123ec
        String childDirectory = code.charAt(0) + File.separator + code.charAt(1); // 5/4
        // 建立指定目錄
        File file = new File(storeDirectory, childDirectory);
        if (!file.exists()) {
            file.mkdirs();
        }
        return childDirectory;
    }

    // 普通表單項
    private void processFormField(FileItem fileitem) {
        try {
            String fieldname = fileitem.getFieldName();// 字段名
            String fieldvalue = fileitem.getString("UTF-8");// 字段值
            System.out.println(fieldname + "=" + fieldvalue);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}