本文目录一览：

1. jsp实现文件的下载
2. jsp 如何实现文件上传和下载功能？
3. jsp页面如何实现下载文档

jsp实现文件的下载

<%@ page language="java" import="java.io.*,java.net.*" contentType="application/x-msdownload" pageEncoding="UTF-8" %>

// 关于文件下载时采用文件流输出的方式处理： // 加上response.reset()，并且所有的%>后面不要换行，包括最后一个；

String url = request.getParameter("url");
System.out.print(url);
int k = url.lastIndexOf("\\");
String url1 = url.substring(k + 1, url.length());
response.reset(); // 可以加也可以不加
response.setContentType("application/x-download");
String filedownload = url;
String filedisplay = url1;
filedisplay = URLEncoder.encode(filedisplay, "UTF-8");
response.addHeader("Content-Disposition", "attachment;filename=" + filedisplay);
OutputStream outp = null;
FileInputStream in = null;
try {
    outp = response.getOutputStream();
    in = new FileInputStream(filedownload);
    byte[] b = new byte[1024];
    int i = 0;
    while ((i = in.read(b)) > 0) {
        outp.write(b, 0, i);
    }
    out.clear();
    out = pageContext.pushBody();
    outp.flush();
} catch (Exception e) {
    System.out.println("Error!");
} finally {
    if (in != null) {
        in.close();
        in = null;
    }
    if (outp != null) {
        outp.close();
        outp = null;
    }
}
%>

jsp 如何实现文件上传和下载功能？

上传：

MyjspForm mf = (MyjspForm) form; // TODO Auto-generated method stub
FormFile fname = mf.getFname();
byte[] fn = fname.getFileData();
OutputStream out = new FileOutputStream("D:\\" + fname.getFileName());
Date date = new Date();
String title = fname.getFileName();
String url = "d:\\" + fname.getFileName();
Upload ul = new Upload();
ul.setDate(date);
ul.setTitle(title);
ul.setUrl(url);
UploadDAO uld = new UploadDAO();
uld.save(ul);
out.write(fn);
out.close();

下载：

DownloadForm downloadForm = (DownloadForm) form;
String fname = request.getParameter("furl");
FileInputStream fi = new FileInputStream(fname);
byte[] bt = new byte[fi.available()];
fi.read(bt);
// 设置文件是下载还是打开以及打开的方式msdownload表示下载；设置字符集，主要是解决文件中的中文信息
response.setContentType("application/msdownload;charset=gbk");
// 文件下载后的默认保存名及打开方式
String contentDisposition = "attachment; filename=" + "java.txt";
response.setHeader("Content-Disposition", contentDisposition);
// 设置下载长度
response.setContentLength(bt.length);
ServletOutputStream sos = response.getOutputStream();
sos.write(bt);
return null;

jsp页面如何实现下载文档

jsp页面下载文档是在jsp中有一个<a>标签，当用户点击<a>标签的时候下载文件。 一般采用href属性直接指向一个服务器地址，只要链接的文件存在，就会弹出保存对话框。 点击<a>标签先执行onclick事件，再请求href中指向的地址。 前端jsp：

<a href="#" onclick="javascript:downloadtest('${app.id}')" id="pluginurl" style="color: #83AFE2;text-decoration:underline;"></a>

然后在js中：

function downloadtest(id) {
    var url = "<%=request.getContextPath()%>/app/download/" + id;
    $("#pluginurl").attr("href", url);
}

后台处理下载逻辑的java代码：

/**
 * 下载文件
 * @param id appid
 * @param response
 */
@RequestMapping(value = "/download/{id}")
public void download(@PathVariable String id, HttpServletResponse response) {
    String filepath = "";
    Result result = appService.getAppById(id);
    App app = (App) result.getMap().get("app");
    if (app == null) {
        return;
    }
    filepath = app.getUrl();
    File file = new File(filepath);
    InputStream inputStream = null;
    OutputStream outputStream = null;
    byte[] b = new byte[1024];
    int len = 0;
    try {
        inputStream = new FileInputStream(file);
        outputStream = response.getOutputStream();
        response.setContentType("application/force-download");
        String filename = file.getName();
        filename = filename.substring(36, filename.length());
        response.addHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(filename, "UTF-8"));
        response.setContentLength((int) file.length());
        while ((len = inputStream.read(b)) != -1) {
            outputStream.write(b, 0, len);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
                inputStream = null;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (outputStream != null) {
            try {
                outputStream.close();
                outputStream = null;
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}