文件上传下载：commons-fileupload + Servlet 2.5

数据库：MySQL

开发技术：JSP + Servlet 2.5

第三方的上传组件：
　　commons-fileupload
　　connons-io

---

上传页面
1、form表单需要增加：enctype="multipart/form-data" 以字节流形式
2、form表单里面增加上传组件：input="file"
3、取消上传：<button onclick="javascript:window.opener == null;window.close();">取消上传</button>

<form id="form1" method="post" action="upload" enctype="multipart/form-data">
　　<table>
   　　　　<tr>
              <td width="25%" align="right">上传文件：</td>
              <td><input id="file1" type="file" NAME="file1" style="width: 300px;"></td>
          </tr>
          <tr align="center" valign="middle">
              <td height="60" colspan="2">
                 <input type="submit" id="BtnOK" value="确认上传">
                 <button onclick="javascript:window.opener == null;window.close();">取消上传</button>
              </td>
           </tr>
           <tr align="center" valign="middle">
               测试非表单控件的值接收：<td height="60" colspan="2"><input type="text" name="possess" value="非提交控件的值"></td>
           </tr>
　　</table>
</form>

代码：
工具类 MutiFileUpload.java 对fileupload组件进行简单封装

import java.io.UnsupportedEncodingException;

import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;  

import javax.servlet.http.HttpServletRequest;  

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;  

/**
 * 当读取上传表单的各部分时会用到该encoding，如果没有指定
 * encoding * 则使用系统缺省的encoding。建议在这里设置成utf-8，并把jsp
 * 的charset也设置成utf-8，否则可能会出现乱码。
 *
 */
@SuppressWarnings("unchecked")
public class MutiFileUpload{  

　 public Map<String,String> parameters ;　　　　//保存form表单域中非上传控件的值
   public Map<String,FileItem> files;　　　　　　//保存上传的文件
  
　　//将文件保存在内存还是磁盘临时文件夹的默认临界值，值为10240，即10kb
    private int sizeThreshold = DiskFileItemFactory.DEFAULT_SIZE_THRESHOLD;  

    private long sizeMax = 1024 * 1024 * 20  ;    　　//上传文件的大小限制;
    private String encoding = "UTF-8";        　　　　//字符编码，当读取上传表单的各部分时会用到该encoding
  
　　// 以上属性的 get/set 方法
    public String getEncoding() {
        return encoding;
    }  

    public void setEncoding(String encoding) {
        this.encoding = encoding;
    }  

    public long getSizeMax() {
        return sizeMax;
    }  

    public void setSizeMax(long sizeMax) {
        this.sizeMax = sizeMax;
    }  

    public int getSizeThreshold() {
        return sizeThreshold;
    }  

    public void setSizeThreshold(int sizeThreshold) {
        this.sizeThreshold = sizeThreshold;
    }
  　　
　　 // 解析请求，这个方法很重要
    public void parse(HttpServletRequest request){
  
　　　　　//保存数据的2个Map初始化
        parameters = new HashMap<String,String>();
        files = new HashMap<String,FileItem>();

        DiskFileItemFactory factory = new DiskFileItemFactory();  

        //设置临界值约束
        factory.setSizeThreshold(sizeThreshold);  

        ServletFileUpload upload = new ServletFileUpload(factory);  

        upload.setSizeMax(sizeMax);
        upload.setHeaderEncoding(encoding);  

        try {  

            List items = upload.parseRequest(request);
            Iterator iterator = items.iterator();
            while(iterator.hasNext()){  

                FileItem item = (FileItem)iterator.next();
                if(item.isFormField()){
                    String fieldName = item.getFieldName();
                    String value = new String(item.getString(encoding));
                    parameters.put(fieldName, value);  

                }else{
                    String fieldName = item.getFieldName();
                    files.put(fieldName, item);
                }
            }  

        } catch (FileUploadException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }  

    /** 得到上传文件的文件名
     * @param item
     * @return
     */
    public String getFileName(FileItem item){  

        String fileName = item.getName();
        fileName = replace(fileName,"\\","/");
        fileName = fileName.substring(fileName.lastIndexOf("/")+1);
        return fileName;  

    }  

    /**字符串替换
     * @param source
     * @param oldString
     * @param newString
     * @return
     */
    public static String replace(String source, String oldString, String newString) {  

        StringBuffer output = new StringBuffer();
        int lengthOfSource = source.length();
        int lengthOfOld = oldString.length();
        int posStart = 0;
        int pos;   

        while ((pos = source.indexOf(oldString, posStart)) >= 0) {  

            output.append(source.substring(posStart, pos));
            output.append(newString);
            posStart = pos + lengthOfOld;
        }  

        if (posStart < lengthOfSource) {
            output.append(source.substring(posStart));
        }  

        return output.toString();
    }
}  

上传Servlet，doGet方法请求doPost。在doPost方法中编写如下代码：

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

        DBUtils db = new DBUtils();

        MutiFileUpload fileUpload = new MutiFileUpload();
        fileUpload.parse(request);
        
　　　　　//这里是打印非上传组件的值，查看是否能够正常接收
        //System.out.println( fileUpload.parameters.get("possess") );  

        Iterator<FileItem> iterator = fileUpload.files.values().iterator();
        while(iterator.hasNext()){  

            FileItem item = iterator.next();
        　　
            String fileName = fileUpload.getFileName(item);
            if( fileName != null && !fileName.equals("")){
                //获取服务器的路径
                String serverPath = request.getSession().getServletContext().getRealPath("");
           　　　//对上传文件重新命名
                String rename = getReName(fileName);
                File file = new File( serverPath+"/upload/"+rename);

                try {

if( !file.isDirectory()){

//上传成功后做数据库操作
                        item.write(file);

                        //数据库操作，这里没有考虑效率，如果是多文件上传，可以考虑SQL的批处理
                        db.saveOrUpdateOrDel("insert into uploadfile(realname,rename_) values(?,?)",
                                new Object[]{fileName ,rename });
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                    //将上传的文件删除
                    if( file.exists()) file.delete();
                }
            }

        }

    }

    /**
     * 以服务器当前时间为为上传文件重新命名
     * @param fileName
     * @return    新文件名
     */
    private String getReName(String fileName){
        int begin = fileName.lastIndexOf(".");
        String extend = fileName.substring(begin, fileName.length());
        return System.currentTimeMillis() + extend;
    }

显示文件下载列表Servlet ，实体类就不再发了，可以在最下面按照SQL语句写

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

        DBUtils db = new DBUtils();
        List<UploadFile> ufs = db.queryForObject("select * from uploadfile", null, UploadFile.class);
        request.setAttribute("filelist", ufs);
        request.getRequestDispatcher("filelist.jsp").forward(request,response);
    }

显示文件下载列表页面

╮(╯▽╰)╭  循环部分发出来就行了，这个filelist.jsp页面本来就这么一点东西

<c:forEach items="${filelist}" var="uf">
      ${uf.realname }&nbsp;&nbsp;&nbsp;<a href="down?re=${uf.rename_}&real=${uf.realname}">下载</a><br>
</c:forEach>

文件下载Servlet

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

        //获取下载文件的名字
        String re = request.getParameter("re");
        //获取下载文件的真实名字
        String real = request.getParameter("real");

        //获取服务器路径
        String serverPath = request.getSession().getServletContext().getRealPath("");
        File f = new File( serverPath+"/upload/"+re);

        if(    f.exists()    ){
            FileInputStream  fis = new FileInputStream(f);
            //手动转码，示例中是GET请求，要么手动转码，要么在过滤器中进行GET请求处理，当然能在服务器直接配置get请求编码就一劳永逸了
            String filename = new String(real.getBytes("ISO8859-1"),"UTF-8");
            byte[] b = new byte[fis.available()];
            fis.read(b);
            response.setCharacterEncoding("UTF-8");
            response.setHeader("Content-Disposition","attachment; filename="+filename );
            //获取响应报文输出流对象
            ServletOutputStream  out =response.getOutputStream();
            out.write(b);
            out.flush();
            out.close();
        }     

    }  

MySQL 数据库部分

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
--  Table structure for `uploadfile`
-- ----------------------------
DROP TABLE IF EXISTS `uploadfile`;
CREATE TABLE `uploadfile` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `realname` varchar(255) NOT NULL COMMENT '上传前的文件名字',
  `rename_` varchar(255) NOT NULL COMMENT '重新命名',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

SET FOREIGN_KEY_CHECKS = 1;