For example, i would like to download one zip file and one csv file in one response. Is there any way other than compressing these two files in one zip file.
Although ServletResponse is not meant to do this, we could programmatically tweak it to send multiple files, which all client browsers except IE seems to handle properly. A sample code snippet is given below.
response.setContentType("multipart/x-mixed-replace;boundary=END");
ServletOutputStream out = response.getOutputStream();
out.println("--END");
for(File f:files){
FileInputStream fis = new FileInputStream(file);
BufferedInputStream fif = new BufferedInputStream(fis);
int data = 0;
out.println("--END");
while ((data = fif.read()) != -1) {
out.write(data);
}
fif.close();
out.println("--END");
out.flush();
}
out.flush();
out.println("--END--");
out.close();
This will not work in IE browsers.
N.B - Try Catch blocks not included
Code developed by Jason Hunter to handle servlet request and response having multiple parts has been the defacto since years. You can find it at servlets.com
No you can not do that. The reason is that whenever you want to sent any data in request you use steam available in request and retrive this data using request.getRequestParameter("streamParamName").getInputStream(), also please make a note if you have already consumed this stream once you will not be able to get it again.
The example mentioned above is a tweak that google also uses in sending multipart email with multiple attachments. To achieve that they define boundaries for each attachment and client have to take care of these boundaries while retrieving this information and rendering it.
Related
For example, i would like to download one zip file and one csv file in one response. Is there any way other than compressing these two files in one zip file.
Although ServletResponse is not meant to do this, we could programmatically tweak it to send multiple files, which all client browsers except IE seems to handle properly. A sample code snippet is given below.
response.setContentType("multipart/x-mixed-replace;boundary=END");
ServletOutputStream out = response.getOutputStream();
out.println("--END");
for(File f:files){
FileInputStream fis = new FileInputStream(file);
BufferedInputStream fif = new BufferedInputStream(fis);
int data = 0;
out.println("--END");
while ((data = fif.read()) != -1) {
out.write(data);
}
fif.close();
out.println("--END");
out.flush();
}
out.flush();
out.println("--END--");
out.close();
This will not work in IE browsers.
N.B - Try Catch blocks not included
Code developed by Jason Hunter to handle servlet request and response having multiple parts has been the defacto since years. You can find it at servlets.com
No you can not do that. The reason is that whenever you want to sent any data in request you use steam available in request and retrive this data using request.getRequestParameter("streamParamName").getInputStream(), also please make a note if you have already consumed this stream once you will not be able to get it again.
The example mentioned above is a tweak that google also uses in sending multipart email with multiple attachments. To achieve that they define boundaries for each attachment and client have to take care of these boundaries while retrieving this information and rendering it.
I am trying to download the pdf content from the internet and download it to a local file.
I am using iText for reading the pdf and using Java stream to write it.
After writing the file, new file can not be opened in the PDF reader.
PdfReader reader = new PdfReader(strURL);
FileOutputStream fos = new FileOutputStream(new File(fileName));
fos.write(reader.getPageContent(1));
fos.flush();
fos.close();
I am trying to get the PDf from this link
I am debugged few things. Here are the findings.
reader.getEofPos()
gives 291633, Which is same as file length.But
reader.getPageContent(1).length;
gives only 42360 bytes. Clearly byte read are less than the actual size.
Only one page of pdf is present
reader.getNumberOfPages() =1
Do i need to specify few more things to reader to read the entire pdf file?
If all you're trying to do is download a PDF from the internet and save it locally, this can be accomplished using a simple HTTP web request. An internet download is normally just an HTTP GET request, which you can accomplish by doing something like this:
URLConnection connection = new URL(url).openConnection();
connection.setRequestProperty("Accept-Charset", charset);
InputStream response = connection.getInputStream();
Once you get the response, you can save the bytes to a path of your choosing.
I'm currently working on a project that is done in Java, on google appengine. i have above 2000 records
Appengine does not allow files to be stored so any on-disk representation objects cannot be used. Some of these include the File class.
I want to write data and export it to a few csv files, the user to download it.
How may I do this without using any File classes? I'm not very experienced in file handling so I hope you guys can advise me.
Thanks.
Just generate the csv in memory using a StringBuffer and then use StringBuffer.toString().getBytes() to get a byte array which can then be sent to your output stream.
For instance if using a servlet in GAE:
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
StringBuffer buffer = new StringBuffer();
buffer.append("header1, header2, header3\n");
buffer.append("row1column1, row1column2, row1column3\n");
buffer.append("row2column1, row2column2, row2column3\n");
// Add more CSV data to the buffer
byte[] bytes = buffer.toString().getBytes();
// This will suggest a filename for the browser to use
resp.addHeader("Content-Disposition", "attachment; filename=\"myFile.csv\"");
resp.getOutputStream().write(bytes, 0, bytes.length);
}
More information about GAE Servlets
More information about Content-Disposition
You can store data in memory using byte arrays, stings and streams. For example,
ByteArrayOutputStream csv = new ByteArrayOutputStream();
PrintStream printer = new PrintStream(csv);
printer.println("a;b;c");
printer.println("1;2;3");
printer.close();
csv.close();
Then in your Servlet you can serve your csv.toByteArray() as a stream. Some example is given here: Implementing a simple file download servlet.
You can use OpenCSV library in Google App Engine.
I need to provide a feature where user can download reports in excel/csv format in my web application. Once i made a module in web application which creates excel and then read it and sent to browser. It was working correctly. This time i don't want to generate excel file, as i don't have that level of control over file systems. I guess one way is to generate appropriate code in StringBuffer and set correct contenttype(I am not sure about this approach). Other team also has this feature but they are struggling when data is very large. What is the best way to provide this feature considering size of data could be very huge. Is it possible to send data in chunk without client noticing(except delay in downloading).
One issue i forgot to add is when there is very large data, it also creates problem in server side (cpu utilization and memory consumption). Is it possible that i read fixed amount of records like 500, send it to client, then read another 500 till completed.
You can also generate HTML instead of CSV and still set the content type to Excel. This is nice for colouring and styled text.
You can also use gzip compression when the client accepts that compression. Normally there are standard means, like a servlet filter.
Never a StringBuffer or the better StringBuilder. Better streaming it out. If you do not (cannot) call setContentength, the output goes chunked (without predictive progress).
URL url = new URL("http://localhost:8080/Works/images/address.csv");
response.setHeader("Content-Type", "text/csv");
response.setHeader("Content-disposition", "attachment;filename=myFile.csv");
URLConnection connection = url.openConnection();
InputStream stream = connection.getInputStream();
BufferedOutputStream outs = new BufferedOutputStream(response.getOutputStream());
int len;
byte[] buf = new byte[1024];
while ((len = stream.read(buf)) > 0) {
outs.write(buf, 0, len);
}
outs.close();
This problem seems to happen inconsistently. We are using a java applet to download a file from our site, which we store temporarily on the client's machine.
Here is the code that we are using to save the file:
URL targetUrl = new URL(urlForFile);
InputStream content = (InputStream)targetUrl.getContent();
BufferedInputStream buffered = new BufferedInputStream(content);
File savedFile = File.createTempFile("temp",".dat");
FileOutputStream fos = new FileOutputStream(savedFile);
int letter;
while((letter = buffered.read()) != -1)
fos.write(letter);
fos.close();
Later, I try to access that file by using:
ObjectInputStream keyInStream = new ObjectInputStream(new FileInputStream(savedFile));
Most of the time it works without a problem, but every once in a while we get the error:
java.io.StreamCorruptedException: invalid stream header: 0D0A0D0A
which makes me believe that it isn't saving the file correctly.
I'm guessing that the operations you've done with getContent and BufferedInputStream have treated the file like an ascii file which has converted newlines or carriage returns into carriage return + newline (0x0d0a), which has confused ObjectInputStream (which expects serialized data objects.
If you are using an FTP URL, the transfer may be occurring in ASCII mode.
Try appending ";type=I" to the end of your URL.
Why are you using ObjectInputStream to read it?
As per the javadoc:
An ObjectInputStream deserializes primitive data and objects previously written using an ObjectOutputStream.
Probably the error comes from the fact you didn't write it with ObjectOutputStream.
Try reading it wit FileInputStream only.
Here's a sample for binary ( although not the most efficient way )
Here's another used for text files.
There are 3 big problems in your sample code:
You're not just treating the input as bytes
You're needlessly pulling the entire object into memory at once
You're doing multiple method calls for every single byte read and written -- use the array based read/write!
Here's a redo:
URL targetUrl = new URL(urlForFile);
InputStream is = targetUrl.getInputStream();
File savedFile = File.createTempFile("temp",".dat");
FileOutputStream fos = new FileOutputStream(savedFile);
int count;
byte[] buff = new byte[16 * 1024];
while((count = is.read(buff)) != -1) {
fos.write(buff, 0, count);
}
fos.close();
content.close();
You could also step back from the code and check to see if the file on your client is the same as the file on the server. If you get both files on an XP machine, you should be able to use the FC utility to do a compare (check FC's help if you need to run this as a binary compare as there is a switch for that). If you're on Unix, I don't know the file compare program, but I'm sure there's something.
If the files are identical, then you're looking at a problem with the code that reads the file.
If the files are not identical, focus on the code that writes your file.
Good luck!