JSP code


JSP code

Can somebody provide a line by line explanation of the following code. The code is used to upload and download an image.

<%@ page import="java.io.*" %>
<%@ page import="java.sql.*" %>

String saveFile="";
String contentType = request.getContentType();
if ((contentType != null) && (contentType.indexOf("multipart/form-data") >= 0)) {
DataInputStream in = new DataInputStream(request.getInputStream());
int formDataLength = request.getContentLength();
byte dataBytes[] = new byte[formDataLength];
int byteRead = 0;
int totalBytesRead = 0;
while (totalBytesRead < formDataLength) {
byteRead = in.read(dataBytes, totalBytesRead,formDataLength);
totalBytesRead += byteRead;
String file = new String(dataBytes);
saveFile = file.substring(file.indexOf("filename=\"") + 10);
saveFile = saveFile.substring(0, saveFile.indexOf("\n"));
saveFile = saveFile.substring(saveFile.lastIndexOf("\\") + 1,saveFile.indexOf("\""));
int lastIndex = contentType.lastIndexOf("=");
String boundary = contentType.substring(lastIndex + 1,contentType.length());
int pos;
pos = file.indexOf("filename=\"");
pos = file.indexOf("\n", pos) + 1;
pos = file.indexOf("\n", pos) + 1;
pos = file.indexOf("\n", pos) + 1;
int boundaryLocation = file.indexOf(boundary, pos) - 4;
int startPos = ((file.substring(0, pos)).getBytes()).length;
int endPos = ((file.substring(0, boundaryLocation)).getBytes()).length;
File f = new File(saveFile);
FileOutputStream fileOut = new FileOutputStream(f);
fileOut.write(dataBytes, startPos, (endPos - startPos));
%><Br><table border="2"><tr><td><b>You have successfully upload the file by the name of:</b>
<% out.println(saveFile);%></td></tr></table>
<a href="download.jsp?f=<%=saveFile%>">Download</a>

/*Code to download an image*/
<%@ page import="java.util.*,java.io.*"%>
<%@ page import="java.net.*"%>
public static String getMimeType(String fileUrl)
throws java.io.IOException, MalformedURLException
String type = null;
URL u = new URL(fileUrl);
URLConnection uc = null;
uc = u.openConnection();
type = uc.getContentType();
return type;

String file=request.getParameter("f");
File f = new File (file);
String filename=f.getName();
String type=getMimeType("file:"+file);

response.setContentType (type);
response.setHeader ("Content-Disposition", "attachment; filename=\""+filename+"\"");

String name = f.getName().substring(f.getName().lastIndexOf("/") + 1,f.getName().length());
InputStream in = new FileInputStream(f);
ServletOutputStream outs = response.getOutputStream();

int bit = 256;
int i = 0;
try {
while ((bit) >= 0) {
bit = in.read();
} catch (IOException ioe) {
View Answers

April 28, 2010 at 11:52 AM

Hi Friend,

In uploading a file,
The method request.getContentType() provides the content type information from the jsp header. Then check the two conditions ((contentType != null) && (contentType.indexOf("multipart/form-data") >= 0)). If the condition is true, create an object of DataInputStream and pass the request.getInputstream() method of Inputstream class to its object. A DataInputstream read primitive Java data types from an underlying input stream.

To get the length of the content type, the method request.getContentLength() is used. Convert the uploaded file into the byte by using while loop and pass the array of dataBytes to the variable file. To save file name, we are using substring() method. After creating sub-string of string, extract the index of file. Then create a new file of same name and write the content in the file using FileOutputStream.

In downloading a file,
we have created a method that will return the mime type of the uploaded file which is then used for setting the content type and character encoding for the page. The setHeader() method creates a HTTP header and allow the browser to show a pop up a "save as" box. The whole data of the file has been read and written to the attached file using input and output streams.



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