servlet实现文件的上载，下载

一、如何使用

如果此Servlet命名为download，请求的URL为：/download?path=xxx，请求后出现下载窗口：

 

二、源码

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

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

public class FileDownload extends HttpServlet {

  protected void service(HttpServletRequest req, HttpServletResponse res)
      throws ServletException, IOException {

    // 服务器相对路径
    String path = req.getParameter("path");
    // 服务器绝对路径
    path = getServletContext().getRealPath("/") + path;

    // 检查文件是否存在
    File obj = new File(path);
    if (!obj.exists()) {
      res.setContentType("text/html;charset=GBK");
      res.getWriter().print("指定文件不存在！");
      return;
    }

    // 读取文件名：用于设置客户端保存时指定默认文件名
    int index = path.lastIndexOf("//"); // 前提：传入的path字符串以“/”表示目录分隔符
    String fileName = path.substring(index + 1);

    // 写流文件到前端浏览器
    ServletOutputStream out = res.getOutputStream();
    res.setHeader("Content-disposition", "attachment;filename=" + fileName);
    BufferedInputStream bis = null;
    BufferedOutputStream bos = null;
    try {
      bis = new BufferedInputStream(new FileInputStream(path));
      bos = new BufferedOutputStream(out);
      byte[] buff = new byte[2048];
      int bytesRead;
      while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {
        bos.write(buff, 0, bytesRead);
      }
    } catch (IOException e) {
      throw e;
    } finally {
      if (bis != null)
        bis.close();
      if (bos != null)
        bos.close();
    }
  }

}

三、web.xml配置

<servlet>
    <servlet-name>FileDownload</servlet-name>
    <servlet-class>com.fastunit.test.FileDownload</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>FileDownload</servlet-name>
    <url-pattern>/download</url-pattern>
</servlet-mapping>

四、补充说明

本例只是一个简单实现，应用时需要在实际环境中处理以下问题：
1. 权限问题：结合实际系统增加用户权限控制
2. 中文文件名：中文问题与运行环境有关，不同环境下解决方式也有差异，一般可通过转码来解决。
3. 文件类型：文件类型统一时可直接指定，如res.setContentType("application/zip")；文件类型不确定时可不设、设一个不存在的、或通过解析文件名后缀来设置，以实际测试通过为准。

4. 以上代码应该有个doget dopost的方法。附带一个上传文件代码，令下载文件正确代码

 

 

 

上传：需要导入两个包：commons-fileupload-1.2.1.jar,commons-io-1.4.jarimport java.io.File;import java.io.IOException;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.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;/** * 上传附件 * @author new * */public class UploadAnnexServlet extends HttpServlet { private static String path = ""; public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  doPost(request, response); } /*  * post处理  * (non-Javadoc)  * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)  */ public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  path = this.getServletContext().getRealPath("/upload");  try {   DiskFileItemFactory factory = new DiskFileItemFactory();   ServletFileUpload up = new ServletFileUpload(factory);   List<FileItem> ls = up.parseRequest(request);   for (FileItem fileItem : ls) {    if (fileItem.isFormField()) {     String FieldName = fileItem.getFieldName();     //getName()返回的是文件名字 普通域没有文件 返回NULL     //                    String Name = fileItem.getName();     String Content = fileItem.getString("gbk");     request.setAttribute(FieldName, Content);    } else {         String nm = fileItem.getName().substring(       fileItem.getName().lastIndexOf("//") + 1);     File mkr = new File(path, nm);     if (mkr.createNewFile()) {      fileItem.write(mkr);//非常方便的方法     }     request.setAttribute("result", "上传文件成功！");    }   }  } catch (Exception e) {   e.printStackTrace();   request.setAttribute("result", "上传失败，请查找原因，重新再试！");  }  request.getRequestDispatcher("/pages/admin/annex-manager.jsp").forward(    request, response); }} 下载（i/o流）无需导包：import java.io.IOException;import java.net.URLEncoder;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * 下载文件 * @author * */public class DownloadFilesServlet extends HttpServlet { /**  *   */ private static final long serialVersionUID = 8594448765428224944L; public void doGet(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  doPost(request, response); } /*  * 处理请求  * (non-Javadoc)  * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)  */ public void doPost(HttpServletRequest request, HttpServletResponse response)   throws ServletException, IOException {  String name = request.getParameter("fileName");  System.out.print("dddddddddd:" + name);  // web绝对路径  String path = request.getSession().getServletContext().getRealPath("/");  String savePath = path + "upload";  // 设置为下载application/x-download  response.setContentType("application/x-download");  // 即将下载的文件在服务器上的绝对路径  String filenamedownload = savePath + "/" + name;  // 下载文件时显示的文件保存名称  String filenamedisplay = name;  // 中文编码转换  filenamedisplay = URLEncoder.encode(filenamedisplay, "UTF-8");  response.addHeader("Content-Disposition", "attachment;filename="    + filenamedisplay);  try {   java.io.OutputStream os = response.getOutputStream();   java.io.FileInputStream fis = new java.io.FileInputStream(     filenamedownload);   byte[] b = new byte[1024];   int i = 0;   while ((i = fis.read(b)) > 0) {    os.write(b, 0, i);   }   fis.close();   os.flush();   os.close();  } catch (Exception e) {  } }}