之前一直接触文件上传，以为文件下载是什么东西。仔细看了下，才发现其本质就是文件的复制。
下载的关键代码：
private void download(HttpServletRequest request,HttpServletResponse response) throws IOException { File f = new File("c:\095557357.jpg"); response.reset(); response.setContentType("image/jpeg");//设置下载文件的类型 response.setHeader("content-disposition","attachment; filename=text.jpg"); //设置下载的文件名 long fileLength=f.length(); String length1=String.valueOf(fileLength); response.setHeader("Content_Length",length1); //下载文件的大小 InputStream in = new FileInputStream( f ); OutputStream out = response.getOutputStream(); byte[] buffer = new byte[2097152]; int ins = in.read(buffer);//读取字节到buffer中 //ins == -1 时 。就已经是文件的结尾了 while ( ins != -1 ) { out.write(buffer, 0, ins);//将缓存buffer中的数据写到文件中 ins = in.read(buffer); } in.close(); out.flush(); out.close(); }
这是一个servlet，复制文件的代码。
response.setContentType("image/jpeg");
是比较重要的，标明本次下载的是一张图片。
发现之前想简单了，下载不仅仅是IO操作复制文件的。
struts2文件下载：
package com.download; import java.io.*; import org.apache.struts2.ServletActionContext; import com.opensymphony.xwork2.ActionSupport; public class Struts2DownloadAction extends ActionSupport { /** * */ private static final long serialVersionUID = 1L; private String fileName; private InputStream downloadFile; public InputStream getDownloadFile(){ return downloadFile; } public String execute(){ System.out.println(fileName); //downloadFile=new FileInputStream("H:\apache-tomcat-6.0.43\webapps\struts2_1\download\"+fileName); downloadFile=ServletActionContext.getServletContext().getResourceAsStream("download/"+fileName); /** * getResourceAsStream()方法只能使用相对路径，绝对路径会空值 * 如果执意使用绝对路径的话，就不使用该方法，直接使用新建InputStream对象 */ return SUCCESS; } public void setFileName(String fileName) { this.fileName = fileName; } public String getFileName() { return fileName; } public void setDownloadFile(InputStream downloadFile) { this.downloadFile = downloadFile; } } <action name="strutsdownload" class="com.download.Struts2DownloadAction"> <result name="success" type="stream"> <param name="contentType">text/plain</param> <param name="contentDisposition">attachment;fileName="${fileName}"</param> <param name="inputName">downloadFile</param> <param name="bufferSize">1024</param> </result> </action>
注意：
1.结果类型必须要写成 type="stream" ,与之对应的处理类是 org.apache.struts2.dispatcher.StreamResult
2：参数：
1) <param name="contentDisposition">attachment;fileName="${fileName}"</param>
contentDisposition默认是 inline（内联的), 比如说下载的文件是文本类型的，就直接在网页上打开，不能直接打开的才会打开下载框自己选择
2) attachment ：下载时会打开下载框
3) fileName="${fileName}" ：在这定义的名字是一个动态的，该名字是显示在下载框上的文件名字
3.<param name="inputName">downloadFile</param>，这个downloadFile名字要和FileDownload.java类中的getDownloadFile()方法名去掉get 一致
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> <%@ taglib prefix="s" uri="/struts-tags" %> <% 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 'filedownload.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="styles.css"> --> </head> <body> <h1>@选择文件进行下载</h1> <table> <tr> <td>J2EE结构.png</td> <td><a href="<s:url value='strutsdownload'><s:param name='fileName'>J2EE结构.png </s:param></s:url>">下载</a> </td> </tr> <tr> <td>MVC图结构.png</td> <td><a href="<s:url value='strutsdownload'><s:param name='fileName'>MVC图结构.png</s:param></s:url>">下载</a></td> </tr> <tr> <td>JSPModel2.png</td> <!-- <a>中的href写成这个样子是为了方便使用struts2的自动给参数赋值 --> <td><a href="<s:url value='strutsdownload'><s:param name='fileName'>JSPModel2.png</s:param></s:url>">下载</a></td> </tr> </table> </body> </html>
java文件下载的几种方式：
public HttpServletResponse download(String path, HttpServletResponse response) { try { // path是指欲下载的文件的路径。 File file = new File(path); // 取得文件名。 String filename = file.getName(); // 取得文件的后缀名。 String ext = filename.substring(filename.lastIndexOf(".") + 1).toUpperCase(); // 以流的形式下载文件。 InputStream fis = new BufferedInputStream(new FileInputStream(path)); byte[] buffer = new byte[fis.available()]; fis.read(buffer); fis.close(); // 清空response response.reset(); // 设置response的Header response.addHeader("Content-Disposition", "attachment;filename=" + new String(filename.getBytes())); response.addHeader("Content-Length", "" + file.length()); OutputStream toClient = new BufferedOutputStream(response.getOutputStream()); response.setContentType("application/octet-stream"); toClient.write(buffer); toClient.flush(); toClient.close(); } catch (IOException ex) { ex.printStackTrace(); } return response; } public void downloadLocal(HttpServletResponse response) throws FileNotFoundException { // 下载本地文件 String fileName = "Operator.doc".toString(); // 文件的默认保存名 // 读到流中 InputStream inStream = new FileInputStream("c:/Operator.doc");// 文件的存放路径 // 设置输出的格式 response.reset(); response.setContentType("bin"); response.addHeader("Content-Disposition", "attachment; filename="" + fileName + """); // 循环取出流中的数据 byte[] b = new byte[100]; int len; try { while ((len = inStream.read(b)) > 0) response.getOutputStream().write(b, 0, len); inStream.close(); } catch (IOException e) { e.printStackTrace(); } } public void downloadNet(HttpServletResponse response) throws MalformedURLException { // 下载网络文件 int bytesum = 0; int byteread = 0; URL url = new URL("windine.blogdriver.com/logo.gif"); try { URLConnection conn = url.openConnection(); InputStream inStream = conn.getInputStream(); FileOutputStream fs = new FileOutputStream("c:/abc.gif"); byte[] buffer = new byte[1204]; int length; while ((byteread = inStream.read(buffer)) != -1) { bytesum += byteread; System.out.println(bytesum); fs.write(buffer, 0, byteread); } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }
支持在线打开文件的一种方式：
public void downLoad(String filePath, HttpServletResponse response, boolean isOnLine) throws Exception { File f = new File(filePath); if (!f.exists()) { response.sendError(404, "File not found!"); return; } BufferedInputStream br = new BufferedInputStream(new FileInputStream(f)); byte[] buf = new byte[1024]; int len = 0; response.reset(); // 非常重要 if (isOnLine) { // 在线打开方式 URL u = new URL("file:///" + filePath); response.setContentType(u.openConnection().getContentType()); response.setHeader("Content-Disposition", "inline; filename=" + f.getName()); // 文件名应该编码成UTF-8 } else { // 纯下载方式 response.setContentType("application/x-msdownload"); response.setHeader("Content-Disposition", "attachment; filename=" + f.getName()); } OutputStream out = response.getOutputStream(); while ((len = br.read(buf)) > 0) out.write(buf, 0, len); br.close(); out.close(); }
有点累了，不想深究，有时候再补充，先放一点别人那里copy的代码，以供不时之需。