最近在幫同學做大作業，用到了 文件上傳 ，在網上搜了一下，看到了高手寫的很好的代碼，學習了....

    
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 {

	public FileUploadServlet() {
		super();
	}

	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

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

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		final long MAX_SIZE = 3 * 1024 * 1024;// 設置上傳文件最大為 3M
		// 允許上傳的文件格式的列表
		final String[] allowedExt = new String[] { "jpg", "jpeg", "gif", "txt",
				"doc", "docx", "mp3", "wma", "m4a" };
		response.setContentType("text/html");
		// 設置字符編碼為UTF-8, 這樣支持漢字顯示
		response.setCharacterEncoding("UTF-8");

		// 實例化一個硬盤文件工廠,用來配置上傳組件ServletFileUpload
		DiskFileItemFactory dfif = new DiskFileItemFactory();
		dfif.setSizeThreshold(4096);// 設置上傳文件時用于臨時存放文件的內存大小,這里是4K.多于的部分將臨時存在硬盤
		dfif.setRepository(new File(request.getRealPath("/")
				+ "ImagesUploadTemp"));// 設置存放臨時文件的目錄,web根目錄下的ImagesUploadTemp目錄

		// 用以上工廠實例化上傳組件
		ServletFileUpload sfu = new ServletFileUpload(dfif);
		// 設置最大上傳尺寸
		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) {// 處理文件尺寸過大異常
			if (e instanceof SizeLimitExceededException) {
				out.println("文件尺寸超過規定大小:" + MAX_SIZE + "字節<p />");
				out.println("<a href=\"upload.html\" target=\"_top\">返回</a>");
				return;
			}
			e.printStackTrace();
		}
		// 沒有
    
      文件上傳
    
    
		if (fileList == null || fileList.size() == 0) {
			out.println("請選擇上傳文件<p />");
			out.println("<a href=\"upload.html\" target=\"_top\">返回</a>");
			return;
		}
		// 得到所有上傳的文件
		Iterator fileItr = fileList.iterator();
		// 循環處理所有文件
		while (fileItr.hasNext()) {
			FileItem fileItem = null;
			String path = null;
			long size = 0;
			// 得到當前文件
			fileItem = (FileItem) fileItr.next();
			// 忽略簡單form字段而不是上傳域的文件域(<input type="text" />等)
			if (fileItem == null || fileItem.isFormField()) {
				continue;
			}
			// 得到文件的完整路徑
			path = fileItem.getName();
			// 得到文件的大小
			size = fileItem.getSize();
			if ("".equals(path) || size == 0) {
				out.println("請選擇上傳文件<p />");
				out.println("<a href=\"upload.html\" target=\"_top\">返回</a>");
				return;
			}

			// 得到去除路徑的文件名
			String t_name = path.substring(path.lastIndexOf("\\") + 1);
			// 得到文件的擴展名(無擴展名時將得到全名)
			String t_ext = t_name.substring(t_name.lastIndexOf(".") + 1);
			// 拒絕接受規定文件格式之外的文件類型
			int allowFlag = 0;
			int allowedExtCount = allowedExt.length;
			for (; allowFlag < allowedExtCount; allowFlag++) {
				if (allowedExt[allowFlag].equals(t_ext))
					break;
			}
			if (allowFlag == allowedExtCount) {
				out.println("請上傳以下類型的文件<p />");
				for (allowFlag = 0; allowFlag < allowedExtCount; allowFlag++)
					out.println("*." + allowedExt[allowFlag]
							+ "&nbsp;&nbsp;&nbsp;");
				out.println("<p /><a href=\"upload.html\" target=\"_top\">返回</a>");
				return;
			}

			long now = System.currentTimeMillis();
			// 根據系統時間生成上傳后保存的文件名
			String prefix = String.valueOf(now);
			// 保存的最終文件完整路徑,保存在web根目錄下的ImagesUploaded目錄下
			String u_name = request.getRealPath("/") + "ImagesUploaded/"
					+ prefix + "." + t_ext;
			try {
				// 保存文件
				fileItem.write(new File(u_name));
				out.println("
    
      文件上傳
    
    成功. 已保存為: " + prefix + "." + t_ext
						+ " &nbsp;&nbsp;文件大小: " + size + "字節<p />");
				out.println("<a href=\"upload.html\" target=\"_top\">繼續上傳</a>");
			} catch (Exception e) {
				e.printStackTrace();
			}

		}

	}

	public void init() throws ServletException {
		// Put your code here
	}

}

  

至于其他的代碼，我想大家應該都會，就不在這賣弄了。

servlet實現文件上傳