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;}}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{//IEif (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;}}