1. 首先需要下載需要的元件。

下載commons-fileupload-1.2.1-bin.zip，下載網址：

   下載commons-io-1.4-bin.zip，下載網址：

2. 用開源的FileUpload元件，可以很方便的給自己的系統新增功能強大的檔案上傳模組。下圖為檔案上傳的基本流程圖。

3. 將commons-fileupload-1.2.1-bin.zip包中的commons-fileupload-1.2.1.jar檔案和commons-io-1.4-bin.zip包中的commons-io-1.4.jar檔案拷貝到web工程下的WEB-INF\lib目錄下。

4. 在伺服器端建立處理檔案上傳的Servlet類。原始碼如下：

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;

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.FileUploadBase.SizeLimitExceededException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;


public class FileUploadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public FileUploadServlet() {
		super();
	}
	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		this.doPost(request, response);
	}

	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		
		final long MAX_SIZE = 300 * 1024 * 1024;// 設定上傳檔案最大值
		// 允許上傳的檔案格式的列表
		final String[] allowedExt = new String[] {"jpg", "jpeg", "gif", "txt",
				"doc","mp3", "wma", "m4a","rar","zip" };
		response.setContentType("text/html");
		// 設定字元編碼為UTF-8, 統一編碼，處理出現亂碼問題
		response.setCharacterEncoding("UTF-8");

		// 例項化一個硬碟檔案工廠,用來配置上傳元件ServletFileUpload
		DiskFileItemFactory dfif = new DiskFileItemFactory();
		dfif.setSizeThreshold(4096);// 設定上傳檔案時用於臨時存放檔案的記憶體大小,這裡是4K.多於的部分將臨時存在硬碟
		dfif.setRepository(new File(request.getRealPath("/")
				+ "ImagesUploadTemp"));// 設定存放臨時檔案的目錄,web根目錄下的ImagesUploadTemp目錄

		// 用以上工廠例項化上傳元件
		ServletFileUpload sfu = new ServletFileUpload(dfif);
		// 設定最大上傳大小
		sfu.setSizeMax(MAX_SIZE);

		PrintWriter out = response.getWriter();
		// 從request得到所有上傳域的列表
		List fileList = null;
		try {
			fileList = sfu.parseRequest(request);
		} catch (FileUploadException e) {// 處理檔案尺寸過大異常
			if (e instanceof SizeLimitExceededException) {
				out.println("檔案尺寸超過規定大小:" + MAX_SIZE + "位元組<p />");
				out
						.println("<a href=\"FileUpload.html\" target=\"_top\">返回</a>");
				return;
			}
			e.printStackTrace();
		}
		// 沒有檔案上傳
		if (fileList == null || fileList.size() == 0) {
			out.println("請選擇上傳檔案<p />");
			out.println("<a href=\"FileUpload.html\" target=\"_top\">返回</a>");
			return;
		}
		// 得到所有上傳的檔案
		Iterator fileItr = fileList.iterator();
		// 迴圈處理所有檔案
		while (fileItr.hasNext()) {
			FileItem fileItem = null;
			String path = null;
			long size = 0;
			// 得到當前檔案
			fileItem = (FileItem) fileItr.next();
			// 忽略簡單form欄位而不是上傳域的檔案域(<input type="text" />等)
			if (fileItem == null || fileItem.isFormField()) {
				continue;
			}
			// 得到檔案的完整路徑
			path = fileItem.getName();
			// 得到檔案的大小
			size = fileItem.getSize();
			if ("".equals(path) || size == 0) {
				out.println("請選擇上傳檔案<p />");
				out
						.println("<a href=\"FileUpload.html\" target=\"_top\">返回</a>");
				return;
			}

			// 得到去除路徑的檔名
			String t_name = path.substring(path.lastIndexOf("\\") + 1);
			// 得到檔案的副檔名(無副檔名時將得到全名)
			String t_ext = t_name.substring(t_name.lastIndexOf(".") + 1);
			// 拒絕接受規定檔案格式之外的檔案型別
			int allowFlag = 0;
			int allowedExtCount = allowedExt.length;
			for (; allowFlag < allowedExtCount; allowFlag++) {
				if (allowedExt[allowFlag].equals(t_ext))
					break;
			}
			if (allowFlag == allowedExtCount) {
				out.println("請上傳以下型別的檔案<p />");
				for (allowFlag = 0; allowFlag < allowedExtCount; allowFlag++)
					out.println("*." + allowedExt[allowFlag]
							+ "   ");
				out
						.println("<p /><a href=\"FileUpload.html\" target=\"_top\">返回</a>");
				return;
			}

			long now = System.currentTimeMillis();
			// 根據系統時間生成上傳後儲存的檔名
			String prefix = String.valueOf(now);
			// 儲存的最終檔案完整路徑,儲存在web根目錄下的ImagesUploaded目錄下
//			String u_name = request.getRealPath("/") + "ImagesUploaded/"
//					+ prefix + "." + t_ext;
			String filename = prefix + "." + t_ext;
			try {
				// 儲存檔案到C:\\upload目錄下
				fileItem.write(new File("C:\\upload\\"+filename));
				System.out.println(filename);
				out.println("檔案上傳成功. 已儲存為: " + prefix + "." + t_ext
						+ "   檔案大小: " + size + "位元組<p />");
				out
						.println("<a href=\"FileUpload.html\" target=\"_top\">繼續上傳</a>");
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
}
 

 5. 在客戶端建立上傳檔案頁面

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>檔案上傳</title>
</head>
<body>
<form action="FileUploadServlet" method="post"
	enctype="multipart/form-data">
	<input type="file" size="30"
	name="file01" /> <br />
		<input type="file" size="30"
	name="file02" /> <br />
<input name="up" type="submit" value="上傳" /></form>
</body>
</html>