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(); 
}