用java在web环境下上传和下载文件的技巧

 import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; import org.apache.commons.fileupload.*; public class Upload extends HttpServlet { private String uploadPath = "C:upload"; // 上传文件的目录 private String tempPath = "C:uploadtmp"; // 临时文件目录 public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { } }

 public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { try { DiskFileUpload fu = new DiskFileUpload(); // 设置最大文件尺寸，这里是4MB fu.setSizeMax(4194304); // 设置缓冲区大小，这里是4kb fu.setSizeThreshold(4096); // 设置临时目录： fu.setRepositoryPath(tempPath); // 得到所有的文件： List fileItems = fu.parseRequest(request); Iterator i = fileItems.iterator(); // 依次处理每一个文件： while(i.hasNext()) { FileItem fi = (FileItem)i.next(); // 获得文件名，这个文件名包括路径： String fileName = fi.getName(); // 在这里可以记录用户和文件信息 // ... // 写入文件，暂定文件名为a.txt，可以从fileName中提取文件名： fi.write(new File(uploadPath + "a.txt")); } } catch(Exception e) { // 可以跳转出错页面 } }

 public void init() throws ServletException { uploadPath = .... tempPath = .... // 文件夹不存在就自动创建： if(!new File(uploadPath).isDirectory()) new File(uploadPath).mkdirs(); if(!new File(tempPath).isDirectory()) new File(tempPath).mkdirs(); }

 〈?xml version="1.0" encoding="ISO-8859-1"?〉 〈!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd"〉 〈web-app〉 〈servlet〉 〈servlet-name〉Upload〈/servlet-name〉 〈servlet-class〉Upload〈/servlet-class〉 〈/servlet〉 〈servlet-mapping〉 〈servlet-name〉Upload〈/servlet-name〉 〈url-pattern〉/fileupload〈/url-pattern〉 〈/servlet-mapping〉 〈/web-app〉

 〈form action="fileupload" method="post" enctype="multipart/form-data" name="form1"〉 〈input type="file" name="file"〉 〈input type="submit" name="Submit" value="upload"〉 〈/form〉

 Upload up = new Upload(); up.init(request); /** 此处可以调用setSaveDir(String saveDir); 设置保存路径 调用setMaxFileSize(long size)设置上传文件的最大字节. 调用setTagFileName(String)设置上传后文件的名字(只对第一个文件有效) */ up. uploadFile(); 

 package com.inmsg.beans; import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; public class Upload { private String saveDir = "."; //要保存文件的路径 private String contentType = ""; //文档类型 private String charset = ""; //字符集 private ArrayList tmpFileName = new ArrayList(); //临时存放文件名的数据结构 private Hashtable parameter = new Hashtable(); //存放参数名和值的数据结构 private ServletContext context; //程序上下文,用于初始化 private HttpServletRequest request; //用于传入请求对象的实例 private String boundary = ""; //内存数据的分隔符 private int len = 0; //每次从内在中实际读到的字节长度 private String queryString; private int count; //上载的文件总数 private String[] fileName; //上载的文件名数组 private long maxFileSize = 1024 * 1024 * 10; //最大文件上载字节; private String tagFileName = ""; public final void init(HttpServletRequest request) throws ServletException { this.request = request; boundary = request.getContentType().substring(30); //得到内存中数据分界符 queryString = request.getQueryString(); } public String getParameter(String s) { //用于得到指定字段的参数值,重写request.getParameter(String s) if (parameter.isEmpty()) { return null; } return (String) parameter.get(s); } public String[] getParameterValues(String s) { //用于得到指定同名字段的参数数组,重写request.getParameterValues(String s) ArrayList al = new ArrayList(); if (parameter.isEmpty()) { return null; } Enumeration e = parameter.keys(); while (e.hasMoreElements()) { String key = (String) e.nextElement(); if ( -1 != key.indexOf(s + "||||||||||") || key.equals(s)) { al.add(parameter.get(key)); } } if (al.size() == 0) { return null; } String[] value = new String[al.size()]; for (int i = 0; i 〈 value.length; i++) { value[i] = (String) al.get(i); } return value; } public String getQueryString() { return queryString; } public int getCount() { return count; } public String[] getFileName() { return fileName; } public void setMaxFileSize(long size) { maxFileSize = size; } public void setTagFileName(String filename) { tagFileName = filename; } public void setSaveDir(String saveDir) { //设置上载文件要保存的路径 this.saveDir = saveDir; File testdir = new File(saveDir); //为了保证目录存在,如果没有则新建该目录 if (!testdir.exists()) { testdir.mkdirs(); } } public void setCharset(String charset) { //设置字符集 this.charset = charset; } public boolean uploadFile() throws ServletException, IOException { //用户调用的上载方法 setCharset(request.getCharacterEncoding()); return uploadFile(request.getInputStream()); } private boolean uploadFile(ServletInputStream servletinputstream) throws //取得央存数据的主方法 ServletException, IOException { String line = null; byte[] buffer = new byte[256]; while ( (line = readLine(buffer, servletinputstream, charset)) != null) { if (line.startsWith("Content-Disposition: form-data; ")) { int i = line.indexOf("filename="); if (i 〉= 0) { //如果一段分界符内的描述中有filename=,说明是文件的编码内容 String fName = getFileName(line); if (fName.equals("")) { continue; } if (count == 0 && tagFileName.length() != 0) { String ext = fName.substring( (fName.lastIndexOf(".") + 1)); fName = tagFileName + "." + ext; } tmpFileName.add(fName); count++; while ( (line = readLine(buffer, servletinputstream, charset)) != null) { if (line.length() 〈= 2) { break; } } File f = new File(saveDir, fName); FileOutputStream dos = new FileOutputStream(f); long size = 0l; while ( (line = readLine(buffer, servletinputstream, null)) != null) { if (line.indexOf(boundary) != -1) { break; } size += len; if (size 〉 maxFileSize) { throw new IOException("文件超过" + maxFileSize + "字节!"); } dos.write(buffer, 0, len); } dos.close(); } else { //否则是字段编码的内容 String key = getKey(line); String value = ""; while ( (line = readLine(buffer, servletinputstream, charset)) != null) { if (line.length() 〈= 2) { break; } } while ( (line = readLine(buffer, servletinputstream, charset)) != null) { if (line.indexOf(boundary) != -1) { break; } value += line; } put(key, value.trim(), parameter); } } } if (queryString != null) { String[] each = split(queryString, "&"); for (int k = 0; k 〈 each.length; k++) { String[] nv = split(each[k], "="); if (nv.length == 2) { put(nv[0], nv[1], parameter); } } } fileName = new String[tmpFileName.size()]; for (int k = 0; k 〈 fileName.length; k++) { fileName[k] = (String) tmpFileName.get(k); //把ArrayList中临时文件名倒入数据中供用户调用 } if (fileName.length == 0) { return false; //如果fileName数据为空说明没有上载任何文件 } return true; } private void put(String key, String value, Hashtable ht) { if (!ht.containsKey(key)) { ht.put(key, value); } else { //如果已经有了同名的KEY,就要把当前的key更名,同时要注意不能构成和KEY同名 try { Thread.currentThread().sleep(1); //为了不在同一ms中产生两个相同的key } catch (Exception e) {} key += "||||||||||" + System.currentTimeMillis(); ht.put(key, value); } } /* 调用ServletInputstream.readLine(byte[] b,int offset,length)方法,该方法是从ServletInputstream流中读一行 到指定的byte数组,为了保证能够容纳一行,该byte[]b不应该小于256,重写的readLine中,调用了一个成员变量len为 实际读到的字节数(有的行不满256),则在文件内容写入时应该从byte数组中写入这个len长度的字节而不是整个byte[] 的长度,但重写的这个方法返回的是String以便分析实际内容,不能返回len,所以把len设为成员变量,在每次读操作时 把实际长度赋给它. 也就是说在处理到文件的内容时数据既要以String形式返回以便分析开始和结束标记,又要同时以byte[]的形式写到文件 输出流中. */ private String readLine(byte[] Linebyte, ServletInputStream servletinputstream, String charset) { try { len = servletinputstream.readLine(Linebyte, 0, Linebyte.length); if (len == -1) { return null; } if (charset == null) { return new String(Linebyte, 0, len); } else { return new String(Linebyte, 0, len, charset); } } catch (Exception _ex) { return null; } } private String getFileName(String line) { //从描述字符串中分离出文件名 if (line == null) { return ""; } int i = line.indexOf("filename="); line = line.substring(i + 9).trim(); i = line.lastIndexOf(""); if (i 〈 0 || i 〉= line.length() - 1) { i = line.lastIndexOf("/"); if (line.equals("""")) { return ""; } if (i 〈 0 || i 〉= line.length() - 1) { return line; } } return line.substring(i + 1, line.length() - 1); } private String getKey(String line) { //从描述字符串中分离出字段名 if (line == null) { return ""; } int i = line.indexOf("name="); line = line.substring(i + 5).trim(); return line.substring(1, line.length() - 1); } public static String[] split(String strOb, String mark) { if (strOb == null) { return null; } StringTokenizer st = new StringTokenizer(strOb, mark); ArrayList tmp = new ArrayList(); while (st.hasMoreTokens()) { tmp.add(st.nextToken()); } String[] strArr = new String[tmp.size()]; for (int i = 0; i 〈 tmp.size(); i++) { strArr[i] = (String) tmp.get(i); } return strArr; } } 下载其实非常简单，只要如下处理，就不会发生问题。 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(); }