Servlet 实现文件的上传与下载
这段时间尝试写了一个小web项目，其中涉及到文件上传与下载，虽然网上有很多成熟的框架供使用，但为了学习我还是选择了自己编写相关的代码。当中遇到了很多问题，所以在此这分享完整的上传与下载代码供大家借鉴。
首先是上传的Servlet代码
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.io.UnsupportedEncodingException;
import java.util.Random;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class UpLoad extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final Random RANDOM = new Random();
private String tempFileFolder; //临时文件存放目录
private String fileFolder; //存文件的目录
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//step 1 将上传文件流写入到临时文件
File tempFile = getTempFile();
writeToTempFile(request.getInputStream(), tempFile);
//step 2从临时文件中取得上传文件流
RandomAccessFile randomFile = new RandomAccessFile(tempFile, "r");
//step 3取得文件名称
String filename = getFileName(randomFile);
//step 4检查存放文件的目录在不在
checkFold();
//step 5保存文件
long fileSize = saveFile(randomFile, filename);
//step 6关闭流对像,删除临时文件
randomFile.close();
tempFile.delete();
}
public void init() throws ServletException {
//获取项目所在目录
String contentPath = getServletContext().getRealPath("/");
this.tempFileFolder = contentPath + "files/_tmp";
this.fileFolder = contentPath+"files/_file";
}
/**
* 对字符串进行转码
* @param str
* @return 转码后的字符串
*/
private String codeString(String str) {
String s = str;
try {
byte[] temp = s.getBytes("ISO-8859-1");
s = new String(temp, "UTF-8");
return s;
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
return s;
}
}
/**
* 产生临时文件对象
* 会检查临时目录是否存在，如果不存在将创建目录
* @return 临时文件对象
* @throws IOException
*/
private File getTempFile()throws IOException{
File tempFolder = new File(this.tempFileFolder);
if (!tempFolder.exists()){
tempFolder.mkdirs();
}
String tempFileName = this.tempFileFolder+File.separator+Math.abs(RANDOM.nextInt());
File tempFile = new File(tempFileName);
if (!tempFile.exists()){
tempFile.createNewFile();
}
return tempFile;
}
/**
* 将上传的数据流存入临时文件
* @param fileSourcel 上传流
* @param tempFile 临时文件
* @throws IOException
*/
private void writeToTempFile(InputStream fileSourcel,File tempFile)throws IOException{
FileOutputStream outputStream = new FileOutputStream(tempFile);
byte b[] = new byte[1000];
int n ;
while ((n=fileSourcel.read(b))!=-1){
outputStream.write(b,0,n);
}
outputStream.close();
fileSourcel.close();
}
/**
* 从临时文件流中提取文件名称
* @param randomFile
* @return 解析的文件名称
* @throws IOException
*/
private String getFileName(RandomAccessFile randomFile)throws IOException{
String _line;
while((_line=randomFile.readLine())!=null && !_line.contains("form-data; name=\"upload\"")){
}
String filePath = _line;
String filename = filePath.replace("Content-Disposition: form-data; name=\"upload\"; filename=\"", "").replace("\"","");
filename=codeString(filename);
randomFile.seek(0);
return filename;
}
/**
* 获取上传文件的开始位置
* 开始位置会因为from 表单的参数不同而不同
* 如果from表单只上传文件是从第四行开始
* 本例from表单还有一个title的input ， 所以从第八行开始。每多一个参数就加四行。
* @param randomFile
* @return 上传文件的开始位置
* @throws IOException
*/
private long getFileEnterPosition(RandomAccessFile randomFile)throws IOException{
long enterPosition = 0;
int forth = 1;
int n ;
while((n=randomFile.readByte())!=-1&&(forth<=8)){
if(n=='\n'){
enterPosition = randomFile.getFilePointer();
forth++;
}
}
return enterPosition;
}
/**
* 获取上传文件的结束位置
* 结束位置会因为文件类型不同，而不同
* 压缩包是倒数第二行后
* @param randomFile
* @return 文件的结束位置
* @throws IOException
*/
private long getFileEndPosition(RandomAccessFile randomFile)throws IOException{
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++;
}
}
return endPosition;
}
/**
* 检查要保存文件的文件夹是否存在
*/
private void checkFold(){
File file = new File(this.fileFolder);
if (!file.exists()){
file.mkdirs();
}
}
/**
* 将临时文件解析后存放到指定的文件存放目录
* @param randomFile
* @param forthEnterPosition
* @param filename
* @return fileSize
* @throws IOException
*/
private long saveFile(RandomAccessFile randomFile,String filename)throws IOException{
File saveFile = new File(this.fileFolder,filename);
RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile,"rw");
long forthEnterPosition = getFileEnterPosition(randomFile);
long endPosition = getFileEndPosition(randomFile);
//从上传文件数据的开始位置到结束位置，把数据写入到要保存的文件中
randomFile.seek(forthEnterPosition);
long startPoint = randomFile.getFilePointer();
while(startPoint<endPosition){
randomAccessFile.write(randomFile.readByte());
startPoint = randomFile.getFilePointer();
}
long fileSize = randomAccessFile.length();
randomAccessFile.close();
return fileSize;
}
}
接着是下载的Servlet代码
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Download extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final String FILEDIR="files/_file";
private String fileFolder; //存文件的目录
public Download() {
super();
}
public void destroy() {
super.destroy();
// Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// request.setCharacterEncoding("UTF-8");
try{
String fileName = request.getParameter("name");
OutputStream outputStream = response.getOutputStream();
//输出文件用的字节数组，每次向输出流发送600个字节
byte b[] = new byte[600];
File fileload = new File(this.fileFolder,fileName);
fileName=encodeFileName(request,fileName);
//客服端使用保存文件的对话框
response.setHeader("Content-disposition", "attachment;filename="+fileName);
//通知客户文件的长度
long fileLength = fileload.length();
String length = String.valueOf(fileLength);
response.setHeader("Content_length", length);
//读取文件，并发送给客服端下载
FileInputStream inputStream = new FileInputStream(fileload);
int n = 0;
while((n=inputStream.read(b))!=-1){
outputStream.write(b,0,n);
}
}catch(FileNotFoundException fnfe){
fnfe.printStackTrace();
try{
PrintWriter out = response.getWriter();
out.println("下载的文件不存在");
out.flush();
out.close();
}catch(IOException ie){
ie.printStackTrace();
}
}catch(IOException ie){
ie.printStackTrace();
try{
PrintWriter out = response.getWriter();
out.println("下载存在问题");
out.flush();
out.close();
}catch(IOException iex){
iex.printStackTrace();
}
}
}
/**
* Initialization of the servlet. <br>
*
* @throws ServletException if an error occurs
*/
public void init() throws ServletException {
this.fileFolder = getServletContext().getRealPath("/")+"files/_file";
}
private String encodeFileName(HttpServletRequest request,String fileName){
try{
//IE
if (request.getHeader("User-Agent").toUpperCase().indexOf("MSIE") >0){
fileName=URLEncoder.encode(fileName,"UTF-8");
}else{
fileName = new String(fileName.getBytes("UTF-8"),"ISO8859-1");
}
}catch(Exception ex){
ex.printStackTrace();
}
return fileName;
}
}