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data loss during file transfer from applet2servlet

elay Raja
Greenhorn

Joined: Jun 10, 2008
Posts: 27
1.I am uploading a large file from applet to servlet by part by part ie.4MB.
Sometimes when i try to upload a file from intranet,data loss occurs.How to avoid this error.

2.I used to show progress bar for file transfer from applet to servlet.It works fine now.But,after uploading i want to GZip the uploaded file in server side.Hence it obviously take time.How can i show the progress bar in applet till he Gzip completes.I used GZIPOutputStream & JZLibGZipOutputStream (external lib) to write the file in .gz format while uploading itself.But when i decompress the above file, data loss occurs.I had confirmed this by using Runtime instance to gzip the file using linux command using java.For example

Process p= runtime.exec("/bin/gzip"+fileToGzip);
p.waitFor();

if i use this method,i won get the read error or size of file which i get after gzip completes is different from using the above two streams which i mentioned earlier.
For Example, if i use this method, 2GB file compressed into 700MB.gz
if i use GZIPOutputStream ,2GB file compressed into 687MB.gz
if i use JZLibGZipOutputStream ,2GB file compressed into 699MB.gz
Please help me to resolve this issue.

Currently the progress bar shows the status of writing the I/O streams to servlet in applet by making connection to servlet using URL class.In servlet, the above streams written in file using FileOutputStream.

What i need is, till Gzip completes,i want to show the progress bar in applet once again or else any other way is possible?
[ July 16, 2008: Message edited by: elay Raja ]
Joe Ess
Bartender

Joined: Oct 29, 2001
Posts: 8997
    
    9

I wouldn't worry about small file differences. Different implementations and options between gzip programs could account for them (note: the preceding is wild speculation on my part).
However, if you are getting an error trying to open a file you created, you may well have a problem. Usually, errors reading and writing files can be traced to two problems: ReadDoesntDoWhatYouThinkItDoes and AvailableDoesntDoWhatYouThinkItDoes. Another common cause is not flushing and closing a stream when finished.
Without seeing some code, I'm just guessing.


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elay Raja
Greenhorn

Joined: Jun 10, 2008
Posts: 27
thanks for your reply. i had found error in my code.
I used to wrap the gzip stream like this.

OutputStream out =new GZIPOutputStream(new FileOutputStream(filePath,(val > 0)));This code in servlet

val defines the number of parts ie.(4MB).
I have to use like this to gZip, otherwise i cant show the progress bar in applet for gzip porcess.if i decompress using GZIPInputStream, the file decompresses only 4MB. I think the final 4MB part. How to decompress to get the original file size.

please help me to resolve this issue. I have been looking on this issue for the past four days.
Joe Ess
Bartender

Joined: Oct 29, 2001
Posts: 8997
    
    9

You haven't shown us any code that would help us diagnose your problem.
Is your code substantially different from these compress and decompress examples?
If so, perhaps we should take a look.
elay Raja
Greenhorn

Joined: Jun 10, 2008
Posts: 27
ok.Let me explain my scenario with code.

int CHUNK_SIZE = 1000 * 4096;
int nChunks = (int)(fileSize/CHUNK_SIZE);

for (int i=0; i<nChunks; i++){
// this loop transfers every 4MB to servlet till the end of nChunks
HttpURLConnection conn =getServletConnection();
OutputStream out = conn.getOutputStream();
int bytesRead=0;
while(bytesRead < chunkSize) {
int read = bin.read(buf);
counter+=read;
if(read == -1){
break;
}
else if(read > 0){
// Streams writing to servlet.
out.write(buf, 0, read);
bytesRead += read;
setProgressValue((int)(counter/1024)/1024);


Then the above streams read in servlet & written in a single file.
All the 4MB parts are written at the end of the file using the code below:-
out =new GZIPOutputStream(new FileOutputStream((getFile(fileName)), (chunk > 0)));


If i unzip the file using GZIPInputStream, i will get the final 4MB part. the exception which i'm getting is:-

Exception in Unziping :java.util.zip.ZipException: invalid block type
java.util.zip.ZipException: invalid block type
at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:140)
at java.util.zip.GZIPInputStream.read(GZIPInputStream.java:87)
at java.io.FilterInputStream.read(FilterInputStream.java:90)
at enspeed.rm.Gzip.unZip(Gzip.java:63)
at enspeed.rm.Gzip.main(Gzip.java:84)

Please help me. I hope you will get it now. Still you wont, then i will send my code.
Joe Ess
Bartender

Joined: Oct 29, 2001
Posts: 8997
    
    9

Why are you splitting up the file in chunks?
What does getServletConnection() do? If it creates a new HTTP connection, you are probably overwriting the previous chunk on the server side and winding up with only the last one.
 
I agree. Here's the link: http://aspose.com/file-tools
 
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