如何在Web页上实现文件上传

web|上传

public class UploadServlet extends HttpServlet 
{ 
 //default maximum allowable file size is 100k 
 static final int MAX_SIZE = 102400; 
 //instance variables to store root and success message 
 String rootPath, successMessage; 
 /** 
 * init method is called when servlet is initialized. 
 */ 
 public void init(ServletConfig config) throws ServletException 
 { 
 super.init(config); 
 //get path in which to save file 
 rootPath = config.getInitParameter("RootPath"); 
 if (rootPath == null) 
 { 
 rootPath = "/"; 
 } 
 /*Get message to show when upload is complete. Used only if 
 a success redirect page is not supplied.*/ 
 successMessage = config.getInitParameter("SuccessMessage"); 
 if (successMessage == null) 
 { 
 successMessage = "File upload complete!"; 
 } 
 } 
 /** 
 * doPost reads the uploaded data from the request and writes 
 * it to a file. 
 */ 
 public void doPost(HttpServletRequest request, 
 HttpServletResponse response) 
 { 
 ServletOutputStream out=null; 
 DataInputStream in=null; 
 FileOutputStream fileOut=null; 
 try 
 { 
 /*set content type of response and get handle to output 
 stream in case we are unable to redirect client*/ 
 response.setContentType("text/plain"); 
 out = response.getOutputStream(); 
 } 
 catch (IOException e) 
 { 
 //print error message to standard out 
 System.out.println("Error getting output stream."); 
 System.out.println("Error description: " + e); 
 return; 
 } 
 try 
 { 
 //get content type of client request 
 String contentType = request.getContentType(); 
 //make sure content type is multipart/form-data 
 if(contentType != null && contentType.indexOf( 
 "multipart/form-data") != -1) 
 { 
 //open input stream from client to capture upload file 
 in = new DataInputStream(request.getInputStream()); 
 //get length of content data 
 int formDataLength = request.getContentLength(); 
 //allocate a byte array to store content data 
 byte dataBytes[] = new byte[formDataLength]; 
 //read file into byte array 
 int bytesRead = 0; 
 int totalBytesRead = 0; 
 int sizeCheck = 0; 
 while (totalBytesRead < formDataLength) 
 { 
 //check for maximum file size violation 
 sizeCheck = totalBytesRead + in.available(); 
 if (sizeCheck > MAX_SIZE) 
 { 
 out.println("Sorry, file is too large to upload."); 
 return; 
 } 
 bytesRead = in.read(dataBytes, totalBytesRead, 
 formDataLength); 
 totalBytesRead += bytesRead; 
 } 
 //create string from byte array for easy manipulation 
 String file = new String(dataBytes); 
 //since byte array is stored in string, release memory 
 dataBytes = null; 
 /*get boundary value (boundary is a unique string that 
 separates content data)*/ 
 int lastIndex = contentType.lastIndexOf("="); 
 String boundary = contentType.substring(lastIndex+1, 
 contentType.length()); 
 //get Directory web variable from request 
 String directory=""; 
 if (file.indexOf("name=\"Directory\"") > 0) 
 { 
 directory = file.substring( 
 file.indexOf("name=\"Directory\"")); 
 //remove carriage return 
 directory = directory.substring( 
 directory.indexOf("\n")+1); 
 //remove carriage return 
 directory = directory.substring( 
 directory.indexOf("\n")+1); 
 //get Directory 
 directory = directory.substring(0, 
 directory.indexOf("\n")-1); 
 /*make sure user didn't select a directory higher in 
 the directory tree*/ 
 if (directory.indexOf("..") > 0) 
 { 
 out.println("Security Error: You can't upload " + 
 "to a directory higher in the directory tree."); 
 return; 
 } 
 } 
 //get SuccessPage web variable from request 
 String successPage=""; 
 if (file.indexOf("name=\"SuccessPage\"") > 0) 
 { 
 successPage = file.substring( 
 file.indexOf("name=\"SuccessPage\"")); 
 //remove carriage return 
 successPage = successPage.substring( 
 successPage.indexOf("\n")+1); 
 //remove carriage return 
 successPage = successPage.substring( 
 successPage.indexOf("\n")+1); 
 //get success page 
 successPage = successPage.substring(0, 
 successPage.indexOf("\n")-1); 
 } 
 //get OverWrite flag web variable from request 
 String overWrite; 
 if (file.indexOf("name=\"OverWrite\"") > 0) 
 { 
 overWrite = file.substring( 
 file.indexOf("name=\"OverWrite\"")); 
 //remove carriage return 
 overWrite = overWrite.substring( 
 overWrite.indexOf("\n")+1); 
 //remove carriage return 
 overWrite = overWrite.substring( 
 overWrite.indexOf("\n")+1); 
 //get overwrite flag 
 overWrite = overWrite.substring(0, 
 overWrite.indexOf("\n")-1); 
 } 
 else 
 { 
 overWrite = "false"; 
 } 
 //get OverWritePage web variable from request 
 String overWritePage=""; 
 if (file.indexOf("name=\"OverWritePage\"") > 0) 
 { 
 overWritePage = file.substring( 
 file.indexOf("name=\"OverWritePage\"")); 
 //remove carriage return 
 overWritePage = overWritePage.substring( 
 overWritePage.indexOf("\n")+1); 
 //remove carriage return 
 overWritePage = overWritePage.substring( 
 overWritePage.indexOf("\n")+1); 
 //get overwrite page 
 overWritePage = overWritePage.substring(0, 
 overWritePage.indexOf("\n")-1); 
 } 
 //get filename of upload file 
 String saveFile = file.substring( 
 file.indexOf("filename=\"")+10); 
 saveFile = saveFile.substring(0, 
 saveFile.indexOf("\n")); 
 saveFile = saveFile.substring( 
 saveFile.lastIndexOf("\\")+1, 
 saveFile.indexOf("\"")); 
 /*remove boundary markers and other multipart/form-data 
 tags from beginning of upload file section*/ 
 int pos; //position in upload file 
 //find position of upload file section of request 
 pos = file.indexOf("filename=\""); 
 //find position of content-disposition line 
 pos = file.indexOf("\n",pos)+1; 
 //find position of content-type line 
 pos = file.indexOf("\n",pos)+1; 
 //find position of blank line 
 pos = file.indexOf("\n",pos)+1; 
 /*find the location of the next boundary marker 
 (marking the end of the upload file data)*/ 
 int boundaryLocation = file.indexOf(boundary,pos)-4; 
 //upload file lies between pos and boundaryLocation 
 file = file.substring(pos,boundaryLocation); 
 //build the full path of the upload file 
 String fileName = new String(rootPath + directory + 
 saveFile); 
 //create File object to check for existence of file 
 File checkFile = new File(fileName); 
 if (checkFile.exists()) 
 { 
 /*file exists, if OverWrite flag is off, give 
 message and abort*/ 
 if (!overWrite.toLowerCase().equals("true")) 
 { 
 if (overWritePage.equals("")) 
 { 
 /*OverWrite HTML page URL not received, respond 
 with generic message*/ 
 out.println("Sorry, file already exists."); 
 } 
 else 
 { 
 //redirect client to OverWrite HTML page 
 response.sendRedirect(overWritePage); 
 } 
 return; 
 } 
 } 
 /*create File object to check for existence of 
 Directory*/ 
 File fileDir = new File(rootPath + directory); 
 if (!fileDir.exists()) 
 { 
 //Directory doesn't exist, create it 
 fileDir.mkdirs(); 
 } 
 //instantiate file output stream 
 fileOut = new FileOutputStream(fileName); 
 //write the string to the file as a byte array 
 fileOut.write(file.getBytes(),0,file.length()); 
 if (successPage.equals("")) 
 { 
 /*success HTML page URL not received, respond with 
 generic success message*/ 
 out.println(successMessage); 
 out.println("File written to: " + fileName); 
 } 
 else 
 { 
 //redirect client to success HTML page 
 response.sendRedirect(successPage); 
 } 
 } 
 else //request is not multipart/form-data 
 { 
 //send error message to client 
 out.println("Request not multipart/form-data."); 
 } 
 } 
 catch(Exception e) 
 { 
 try 
 { 
 //print error message to standard out 
 System.out.println("Error in doPost: " + e); 
 //send error message to client 
 out.println("An unexpected error has occurred."); 
 out.println("Error description: " + e); 
 } 
 catch (Exception f) {} 
 } 
 finally 
 { 
 try 
 { 
 fileOut.close(); //close file output stream 
 } 
 catch (Exception f) {} 
 try 
 { 
 in.close(); //close input stream from client 
 } 
 catch (Exception f) {} 
 try 
 { 
 out.close(); //close output stream to client 
 } 
 catch (Exception f) {} 
 } 
 } 
}

时间： 2024-12-07 12:29:19

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