servlet实现图片预览、文件上传下载（转载）

来源：互联网发布：java 短链接编辑：程序博客网时间：2024/06/08 17:25

//文件上传package com.imooc.servlet;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class UploadServlet extends HttpServlet {    public void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doPost(req,resp);    }    public void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        //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);        //outputStram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);        System.out.println("filename:" + filename);        //重新定位文件指针到文件头        randomFile.seek(0);        long startPosition = 0;        int i = 1;        //获取文件内容 开始位置        while(( n = randomFile.readByte()) != -1 && i <=4){            if(n == '\n'){                startPosition = randomFile.getFilePointer();                i ++;            }        }        startPosition = randomFile.getFilePointer() -1;        //获取文件内容 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");        //从临时文件当中读取文件内容（根据起止位置获取）        randomFile.seek(startPosition);        while(startPosition < endPosition){            randomAccessFile.write(randomFile.readByte());            startPosition = 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);    }}

//文件下载package com.imooc.servlet;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import javax.servlet.RequestDispatcher;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 {    public 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application/octet-stream            resp.setContentType("application/x-msdownload");            //设置头信息            resp.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\"");            InputStream inputStream = new FileInputStream(file);            ServletOutputStream ouputStream = resp.getOutputStream();            byte b[] = new byte[1024];            int n ;            while((n = inputStream.read(b)) != -1){                ouputStream.write(b,0,n);            }            //关闭流、释放资源            ouputStream.close();            inputStream.close();        }else{            req.setAttribute("errorResult", "文件不存在下载失败！");            RequestDispatcher dispatcher = req.getRequestDispatcher("jsp/01.jsp");            dispatcher.forward(req, resp);        }    }    public void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        doGet(req,resp);    }}

jsp页面<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <base href="<%=basePath%>">    <title>My JSP '01.jsp' starting page</title>    <meta http-equiv="pragma" content="no-cache">    <meta http-equiv="cache-control" content="no-cache">    <meta http-equiv="expires" content="0">        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    <meta http-equiv="description" content="This is my page">    <link rel="stylesheet" type="text/css" href="css/common.css" />    <script type="text/javascript" src="js/jquery-1.11.1.js"></script>    <script type="text/javascript">        $(function(){            $(".thumbs a").click(function(){                var largePath  = $(this).attr("href");                var largeAlt = $(this).attr("title");                $("#largeImg").attr({                    src : largePath,                    alt : largeAlt                });                return false;            });            $("#myfile").change(function(){                $("#previewImg").attr("src","file:///" + $("#myfile").val());            });            var la = $("#large");            la.hide();            $("#previewImg").mousemove(function(e){                la.css({                    top : e.pageY,                    left : e.pageX                }).html('<img src = "' + this.src + '" />').show();            }).mouseout(function(){                la.hide();            });        });         /*  //使用js实现文件上传图片的预览        function showPreview(obj){            var str = obj.value;            document.getElementById("previewImg").innerHTML =                 "<img src = '" + str + "' />";        }        */    </script>  </head>  <body>     <img id="previewImg" src="images/preview.jpg" width="80" height="80" />     <form action="uploadServlet.do" method="post" enctype="multipart/form-data">        请选择图片：<input id="myfile" name="myfile" type="file" onchange="showPreview(this)"/>        <input type="submit" value="提交"  />${result}    </form>    下载：<a href="downloadServlet.do?filename=test.txt">test.txt</a> &nbsp;&nbsp; ${errorResult}    <div id="large"></div>    <hr>    <h2>图片预览</h2>    <p><img id="largeImg" src="images/img1-lg.jpg" alt="Large Image"/></p>    <p class="thumbs">        <a href="images/img2-lg.jpg" title="Image2"><img src="images/img2-thumb.jpg"></a>        <a href="images/img3-lg.jpg" title="Image3"><img src="images/img3-thumb.jpg"></a>        <a href="images/img4-lg.jpg" title="Image4"><img src="images/img4-thumb.jpg"></a>        <a href="images/img5-lg.jpg" title="Image5"><img src="images/img5-thumb.jpg"></a>        <a href="images/img6-lg.jpg" title="Image6"><img src="images/img6-thumb.jpg"></a>    </p>  </body></html>

转载自慕课网《easy实现文件上传下载（David）》视频教程；http://www.imooc.com/video/5566

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