Java文件上传下载

基本原理

文件上传原理
通过为表单元素设置Method=”post” enctype=”multipart/form-data”属性，让表单提交的数据以二进制编码的方式提交，在接收此请求的Servlet中用二进制流来获取内容，就可以取得上传的文件的内容，从而实现文件的上传。

文件下载原理

JSP+Servlet实现文件上传下载

上传

    <form action="<%=path %>/uploadServlet.do" method="post" enctype="multipart/form-data">        请选择图片：<input id="myfile" name="myfile" type="file" >        <input type="submit" value="提交" />    </form>

    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("已接收到请求");        //从request当中获取流信息        InputStream fileSource = req.getInputStream();        String tempFileName = "E:/tempFile";        //tempFile指向临时文件        File tempFile = new File(tempFileName);        //outputSteam文件输出流指向这个临时文件        FileOutputStream outputStream = new FileOutputStream(tempFile);        byte b[] = new byte[1024];        int n;        while((n = fileSource.read(b)) != -1){            outputStream.write(b, 0, n);        }        //关闭输出流、输入流        outputStream.close();        fileSource.close();        //获取上传的文件的名称        RandomAccessFile randomFile = new RandomAccessFile(tempFile, "r");        randomFile.readLine();        String str = randomFile.readLine();        int beginIndex = str.lastIndexOf("\\")+1;        int endIndex = str.lastIndexOf("\"");        String filename = str.substring(beginIndex, endIndex);        //重新定位文件指针到文件头        randomFile.seek(0);        long startPostion = 0;        int i = 1;        //获取文件内容的开始位置        while((n = randomFile.readByte()) != -1 && i <= 4){            if(n == '\n'){                startPostion = randomFile.getFilePointer();                i++;            }        }        startPostion = startPostion - 1;        //获取文件内容的结束位置        randomFile.seek(randomFile.length());        long endPosition = randomFile.getFilePointer();        int j = 1;        while(endPosition >= 0 && j<=2){            endPosition--;            randomFile.seek(endPosition);            if(randomFile.readByte() == '\n'){                j++;            }        }        endPosition = endPosition - 1;        //设置保存文件上传文件的路径        String realPath = getServletContext().getRealPath("/")+"images";        File fileupload = new File(realPath);        if(!fileupload.exists()){            fileupload.mkdir();        }        File saveFile = new File(realPath, filename);        RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile, "rw");        //从临时文件中读取文件内容（根据起止位置获取）        randomAccessFile.seek(startPostion);        while(startPostion > endPosition){            randomAccessFile.write(randomFile.readByte());            startPostion = randomFile.getFilePointer();        }        //关闭输入输出流、删除临时文件        randomAccessFile.close();        randomFile.close();        tempFile.delete();        req.setAttribute("result", "上传成功！");        RequestDispatcher dispatcher = req.getRequestDispatcher("jsp/01.jsp");        dispatcher.forward(req, resp);    }

下载

下载实现思路

<a href="<%=path %>/downloadServlet.do?filename=00.jpg">text.txt</a>

package com.imooc.servlet;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;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 DownloadServlet extends HttpServlet {    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        doGet(req, resp);    }    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //获取文件下载路径        String path = getServletContext().getRealPath("/")+"images/";        String filename = req.getParameter("filename");        File file = new File(path+filename);        if (file.exists()) {            //设置相应类型            resp.setContentType("application/x-msdownlaod");            //设置头信息            resp.setHeader("Content-Disposition", "attachment;filename=\""+filename+"\"");            InputStream inputStream = new FileInputStream(file);            ServletOutputStream outputStream = resp.getOutputStream();            byte b[] = new byte[1024];            int n;            while((n = inputStream.read(b)) != -1){                outputStream.write(b, 0, n);            }            //关闭流、释放资源            outputStream.close();            inputStream.close();        }else{            req.setAttribute("errorResult", "文件不存在，下载失败！");        }    }}

SmartUpload

上传
如下上传文件：

    <form action="smartupload_demo01.jsp" method="post" enctype="multipart/form-data">        选择文件1：<input type="file" name="myfile1"><br/>        选择文件2：<input type="file" name="myfile2"><br/>        选择文件3：<input type="file" name="myfile3"><br/>        <input type="submit" value="上传">    </form>

处理过程如下：

        //设置上传文件保存路径        String filePath = getServletContext().getRealPath("/")+"images";        File file = new File(filePath);        if(!file.exists()){            file.mkdir();        }        SmartUpload su = new SmartUpload();        //初始化对象        su.initialize(getServletConfig(), request, response);        //设置上传文件大小        su.setMaxFileSize(1024*1024*10);        //设置所有文件大小        su.setTotalMaxFileSize(1024*1024*100);        //设置允许用户上传文件类型        su.setAllowedFilesList("txt,jpg,png,gif");        String result    = "上传成功";        //设置禁止上传文件类型        try{            su.setDeniedFilesList("rar,jsp,js");            //上传文件            su.upload();            int count = su.save(filePath);        }catch(Exception e){            e.printStackTrace();            result = "上传失败";        }

异常处理

            if(e.getMessage().indexOf("1015") != -1){                result = "上传失败：上传文件类型不正确！";            }else if(e.getMessage().indexOf("1010") != -1){                result = "上传失败：上传文件类型不正确！";            }else if(e.getMessage().indexOf("1105") != -1){                result = "上传失败：上传文件大小大于允许的最大值！";            }else if(e.getMessage().indexOf("1110") != -1){                result = "上传失败：上传文件总大小大于允许的最大值！";            }

通过SmartUpload获取上传文件的其他属性

        for(int i = 0; i < su.getFiles().getCount(); i++){            org.lxh.smart.File tempFile = su.getFiles().getFile(i);            System.out.println("--------");            System.out.println("表单当中name的值："+tempFile.getFieldName());            System.out.println("上传文件名："+tempFile.getFileName());            System.out.println("上传文件的大小："+tempFile.getSize());            System.out.println("上传文件的拓展名："+tempFile.getFileExt());            System.out.println("上传文件的全名："+tempFile.getFilePathName());            System.out.println("--------");        }

输出结果如下：

表单当中name的值：myfile3上传文件名：2.png上传文件的大小：316681上传文件的拓展名：png上传文件的全名：2.png

下载

下载：<a href="smartDownloadServlet.do?filename=img2-lg.jpg">img2-lg.jpg</a>

SmartDownloadServlet如下：

    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String filename = req.getParameter("filename");        SmartUpload su = new SmartUpload();        su.initialize(getServletConfig(), req, resp);        su.setContentDisposition(null);        try {            su.downloadFile("/images/"+filename);        } catch (SmartUploadException e) {            e.printStackTrace();        }    }

使用SmartUpload实现文件批量下载
如何实现文件的批量下载？

    <form action="smartDownloadServlet.do">        <input type="checkbox"  name="filename" value="img2-lg.jpg">Image2        <input type="checkbox"  name="filename" value="img3-lg.jpg">Image3        <input type="checkbox"  name="filename" value="img4-lg.jpg">Image4        <input type="submit" value="下载">    </form>

servlet处理

        resp.setContentType("application/x-msdownload");        resp.setHeader("Content-Disposition", "attachment;filename=test.zip");        String filepath = getServletContext().getRealPath("/")+"images/";        String[] filenames = req.getParameterValues("filename");        String str = "";        String rt = "\r\n";        ZipOutputStream zipOutputStream  = new ZipOutputStream(resp.getOutputStream());        for(String filename : filenames){            str += filename+rt;            File file = new File(filepath+filename);            zipOutputStream.putNextEntry(new ZipEntry(filename));            FileInputStream fis = new FileInputStream(file);            byte b[] = new byte[1024];            int n = 0;            while((n = fis.read(b)) != -1){                zipOutputStream.write(b, 0, n);            }            zipOutputStream.flush();            fis.close();        }        zipOutputStream.setComment("download success:"+rt+str);        zipOutputStream.flush();        zipOutputStream.close();