Using PrintWriter while downloading a file - java

I have a requirement, where i need to process a set of files and create a compressed zip file out of it and then use it for download. I am using a Servlet for downloading that file, but the download takes quite sometime. So i want the user to know that the servlet is processing the request through a print writer output messsage instead of showing him a blank screen.But everytime i use a printwriter to write something to the screen, the message takes a lot of time to show on the screen and the file doesnt download.
How can i achieve this? Any ides?
Thanks.
Here's my code
OutputStream oStream = null;
DataInputStream dInput = null;
File file = new File(("PATH"));
int length = 0;
try{
DownloadServerLogs.processLogs();
oStream = res.getOutputStream();
res.setContentType("application/zip");
res.setContentLength((int)file.length());
res.setHeader("Content-Disposition",
"attachment;filename=\"" + file.getName() + "\"" );
byte[] bbuf = new byte[BYTES_DOWNLOAD];
dInput = new DataInputStream(new FileInputStream(file));
while ((dInput != null) && ((length = dInput.read(bbuf)) != -1))
{
oStream.write(bbuf,0,length);
}
dInput.close();
oStream.flush();
oStream.close();
}catch(Exception e){
Utility.getLogger().error(e.getMessage(), e);
}

I guess its better to display the message to the client by using something like Javascript (assuming you are using AJAX to invoke the servlet).

Well, it's probably not that safe to do it that way. I'd have a look at the answer below. Not that it's your exact problem, but might be similar.
Most efficient way to create InputStream from OutputStream
Effectively, you are reading and writing on the same thread and my guess is that with the addition of the PrintWriter you are getting deadlocked somewhere.

Related

downloaded file supposed to be .png

i dont know whats wrong with my code, i try to download png from server with sambautil
if (!path.equals("")) {
SambaUtil su = new SambaUtil();
byte[] data = su.openfile(path);
log.info(path);
ByteArrayInputStream inStream = new ByteArrayInputStream(su.openfile(path));
PrintWriter outStream1 = resp.getWriter();
int bytes;
while ((bytes = inStream.read()) != -1) {
outStream1.write(bytes);
}
inStream.close();
outStream1.close();
}
the connection is right, but output data seems wrong
the output
Any idea?
That is because you are taking the bytes that make up the .PNG file and printing it out instead of saving it as a file which is what I think you want to do.
Instead of
PrintWriter outStream1 = resp.getWriter();
Replace with this
OutputStream outStream1 = new FileOutputStream("somefile.png");
Then open the 'somefile.png' and you should be able to see the image that you downloaded via Samba

Resumable upload from Java client to Grails web application?

After almost 2 workdays of Googling and trying several different possibilities I found throughout the web, I'm asking this question here, hoping that I might finally get an answer.
First of all, here's what I want to do:
I'm developing a client and a server application with the purpose of exchanging a lot of large files between multiple clients on a single server. The client is developed in pure Java (JDK 1.6), while the web application is done in Grails (2.0.0).
As the purpose of the client is to allow users to exchange a lot of large files (usually about 2GB each), I have to implement it in a way, so that the uploads are resumable, i.e. the users are able to stop and resume uploads at any time.
Here's what I did so far:
I actually managed to do what I wanted to do and stream large files to the server while still being able to pause and resume uploads using raw sockets. I would send a regular request to the server (using Apache's HttpClient library) to get the server to send me a port that was free for me to use, then open a ServerSocket on the server and connect to that particular socket from the client.
Here's the problem with that:
Actually, there are at least two problems with that:
I open those ports myself, so I have to manage open and used ports myself. This is quite error-prone.
I actually circumvent Grails' ability to manage a huge amount of (concurrent) connections.
Finally, here's what I'm supposed to do now and the problem:
As the problems I mentioned above are unacceptable, I am now supposed to use Java's URLConnection/HttpURLConnection classes, while still sticking to Grails.
Connecting to the server and sending simple requests is no problem at all, everything worked fine. The problems started when I tried to use the streams (the connection's OutputStream in the client and the request's InputStream in the server). Opening the client's OutputStream and writing data to it is as easy as it gets. But reading from the request's InputStream seems impossible to me, as that stream is always empty, as it seems.
Example Code
Here's an example of the server side (Groovy controller):
def test() {
InputStream inStream = request.inputStream
if(inStream != null) {
int read = 0;
byte[] buffer = new byte[4096];
long total = 0;
println "Start reading"
while((read = inStream.read(buffer)) != -1) {
println "Read " + read + " bytes from input stream buffer" //<-- this is NEVER called
}
println "Reading finished"
println "Read a total of " + total + " bytes" // <-- 'total' will always be 0 (zero)
} else {
println "Input Stream is null" // <-- This is NEVER called
}
}
This is what I did on the client side (Java class):
public void connect() {
final URL url = new URL("myserveraddress");
final byte[] message = "someMessage".getBytes(); // Any byte[] - will be a file one day
HttpURLConnection connection = url.openConnection();
connection.setRequestMethod("GET"); // other methods - same result
// Write message
DataOutputStream out = new DataOutputStream(connection.getOutputStream());
out.writeBytes(message);
out.flush();
out.close();
// Actually connect
connection.connect(); // is this placed correctly?
// Get response
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String line = null;
while((line = in.readLine()) != null) {
System.out.println(line); // Prints the whole server response as expected
}
in.close();
}
As I mentioned, the problem is that request.inputStream always yields an empty InputStream, so I am never able to read anything from it (of course). But as that is exactly what I'm trying to do (so I can stream the file to be uploaded to the server, read from the InputStream and save it to a file), this is rather disappointing.
I tried different HTTP methods, different data payloads, and also rearranged the code over and over again, but did not seem to be able to solve the problem.
What I hope to find
I hope to find a solution to my problem, of course. Anything is highly appreciated: hints, code snippets, library suggestions and so on. Maybe I'm even having it all wrong and need to go in a totally different direction.
So, how can I implement resumable file uploads for rather large (binary) files from a Java client to a Grails web application without manually opening ports on the server side?
HTTP GET method have special headers for range retrieval: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.35 It's used by most downloaders to do resumable download from server.
As I understand, there are no standard practice for using this headers for POST/PUT request, but it's up to you, right? You can make pretty standard Grails controller, that will accept standard http upload, with header like Range: bytes=500-999. And controller should put this 500 uploaded bytes from client into file, starting at position 500
At this case you don't need to open any socket, and make own protocols, etc.
P.S. 500 bytes is just a example, probably you're using much bigger parts.
Client Side Java Programming:
public class NonFormFileUploader {
static final String UPLOAD_URL= "http://localhost:8080/v2/mobileApp/fileUploadForEOL";
static final int BUFFER_SIZE = 4096;
public static void main(String[] args) throws IOException {
// takes file path from first program's argument
String filePath = "G:/study/GettingStartedwithGrailsFinalInfoQ.pdf";
File uploadFile = new File(filePath);
System.out.println("File to upload: " + filePath);
// creates a HTTP connection
URL url = new URL(UPLOAD_URL);
HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
httpConn.setDoOutput(true);
httpConn.setRequestMethod("POST");
// sets file name as a HTTP header
httpConn.setRequestProperty("fileName", uploadFile.getName());
// opens output stream of the HTTP connection for writing data
OutputStream outputStream = httpConn.getOutputStream();
// Opens input stream of the file for reading data
FileInputStream inputStream = new FileInputStream(uploadFile);
byte[] buffer = new byte[BUFFER_SIZE];
int bytesRead = -1;
while ((bytesRead = inputStream.read(buffer)) != -1) {
System.out.println("bytesRead:"+bytesRead);
outputStream.write(buffer, 0, bytesRead);
outputStream.flush();
}
System.out.println("Data was written.");
outputStream.flush();
outputStream.close();
inputStream.close();
int responseCode = httpConn.getResponseCode();
if (responseCode == HttpURLConnection.HTTP_OK) {
// reads server's response
BufferedReader reader = new BufferedReader(new InputStreamReader(
httpConn.getInputStream()));
String response = reader.readLine();
System.out.println("Server's response: " + response);
} else {
System.out.println("Server returned non-OK code: " + responseCode);
}
}
}
Server Side Grails Programme:
Inside the controller:
def fileUploadForEOL(){
def result
try{
result = mobileAppService.fileUploadForEOL(request);
}catch(Exception e){
log.error "Exception in fileUploadForEOL service",e
}
render result as JSON
}
Inside the Service Class:
def fileUploadForEOL(request){
def status = false;
int code = 500
def map = [:]
try{
String fileName = request.getHeader("fileName");
File saveFile = new File(SAVE_DIR + fileName);
System.out.println("===== Begin headers =====");
Enumeration<String> names = request.getHeaderNames();
while (names.hasMoreElements()) {
String headerName = names.nextElement();
System.out.println(headerName + " = " + request.getHeader(headerName));
}
System.out.println("===== End headers =====\n");
// opens input stream of the request for reading data
InputStream inputStream = request.getInputStream();
// opens an output stream for writing file
FileOutputStream outputStream = new FileOutputStream(saveFile);
byte[] buffer = new byte[BUFFER_SIZE];
int bytesRead = inputStream.read(buffer);
long count = bytesRead
while(bytesRead != -1) {
outputStream.write(buffer, 0, bytesRead);
bytesRead = inputStream.read(buffer);
count += bytesRead
}
println "count:"+count
System.out.println("Data received.");
outputStream.close();
inputStream.close();
System.out.println("File written to: " + saveFile.getAbsolutePath());
code = 200
}catch(Exception e){
mLogger.log(java.util.logging.Level.SEVERE,"Exception in fileUploadForEOL",e);
}finally{
map <<["code":code]
}
return map
}
I have tried with above code it is worked for me(only for file size 3 to 4MB, but for small size files some bytes of code missing or not even coming but in request header content-length is coming, not sure why it is happening.)

Transmission of files through Socket or HTTP, between Android devices and desktops

I have custom socket client server data (file or text) transmission code. Now when I transfer binary files, some bytes convert onto out of range characters. So I send them in hex string. That works. But for another problem this is not the solution. This has a performance problems as well.
I took help from Java code To convert byte to Hexadecimal.
When I download images from the net, same thing happens. Some bytes change into something else. I have compared bytes by bytes.
Converting into String show ? instead of the symbol. I have tried readers and byte array input stream. I have tried all the examples on the net. What is the mistake I could be doing?
My Code to save bytes to file:
void saveFile(String strFileName){
try{
URL url = new URL(strImageRoot + strFileName);
BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
BufferedWriter bw = new BufferedWriter(new FileWriter(strImageDownloadPath + strFileName));
String line = null;
while ( (line = reader.readLine()) != null) {
bw.write(line);
}
}catch(FileNotFoundException fnfe){
System.out.println("FileNotFoundException occured!!!");
}catch(IOException ioe){
}catch(Exception e){
System.out.println("Exception occured : " + e);
}finally{
System.out.println("Image downloaded!!!");
}
}
i had a similar issue when i was building a Socket client server application. The bytes would be some weird characters and i tried all sorts of things to try and compare them. Then i came across a discussion where some1 pointed out to me that i should use a datainputstream, dataoutstream and let that do the conversion to and from bytes. that worked for me totally. i never touched the bytes at all.
use this code
File root = android.os.Environment.getExternalStorageDirectory();
File dir = new File (root.getAbsolutePath() + "/image");
if(dir.exists()==false) {
dir.mkdirs();
}
URL url = new URL("http://4.bp.blogspot.com/-zqJs1fVcfeY/TiZM7e-pFqI/AAAAAAAABjo/aKTtTDTCgKU/s1600/Final-Fantasy-X-Night-Sky-881.jpg");
//URL url = new URL(DownloadUrl);
//you can write here any link
File file = new File(dir,"Final-Fantasy-X-Night-Sky-881.jpg");
long startTime = System.currentTimeMillis();
//Open a connection to that URL.
URLConnection ucon = url.openConnection();
//* Define InputStreams to read from the URLConnection.
InputStream is = ucon.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);
//* Read bytes to the Buffer until there is nothing more to read(-1).
ByteArrayBuffer baf = new ByteArrayBuffer(6000);
int current = 0;
while ((current = bis.read()) != -1) {
baf.append((byte) current);
}
//Convert the Bytes read to a String.
FileOutputStream fos = new FileOutputStream(file);
fos.write(baf.toByteArray());
fos.flush();
fos.close();
You should take the help of this link: How to encode decode in base64 in Android.
You can send byte array obtained from a file as string by encoding into Base64. This reduces the amount of data transmitted as well.
At the receiving end just decode the string using Base64 and obtain byte array.
Then you can use #Deepak Swami's solution to save bytes in file.
I recently found out that PHP service APIs do not know about what is byte array. Any String can be byte stream at the same time, so the APIs expect Base64 string in the request parameter. Please see the posts:
String to byte array in php
Passing base64 encoded strings in URL
Hence Base64 has quite importance as also it allows you to also save byte arrays in preferences, and increases performance if you have to send file data across network using Serialization.
Happy Coding :-)

How do I do an FTP delete with Java URLConnection?

I have a simple put and get working, but can't seem to find how to do a delete? For reference, the put code is:
BufferedInputStream inStream = null;
FileOutputStream outStream = null;
try {
final String ftpConnectInfo = "ftp://"+user+":"+pass+"#"+destHost+"/"+destFilename+";type=i";
LOGGER.info("Connection String: {}", ftpConnectInfo);
URL url = new URL(ftpConnectInfo);
URLConnection con = url.openConnection();
inStream = new BufferedInputStream(con.getInputStream());
outStream = new FileOutputStream(origFilename);
int i = 0;
byte[] bytesIn = new byte[1024];
while ((i = inStream.read(bytesIn)) >= 0) {
outStream.write(bytesIn, 0, i);
}
}
Is there some way to modify the URL to do a delete?
Based on this discussion on JavaRanch, I'm not sure you can do it by just modifying the URL. Is there any particular reason why you're not just using a library class like Apache commons FTPClient?
I would take a look at commons-net or commons-vfs for Java FTP, what you are doing here is opening an input stream on a file and reading it, while you want to send a command and get an acknowledgment.
I think the URLConnection is just supposed to allow you to read data.
It implements some commands of the FTP protocol to allow you to fetch files. But i don't think there is any way to sneakily encode a DELETE command in a URL to allow you to do what you want.
As other have said: you have to use a full featured FTP client.

Write a binary downloaded file to disk in Java

I have a software that allow to write add-on in javascript files (.js) that allow to use Java function (I don't know if this is common, I never saw java call in javascript file before)
I need to download a binary file from a webserver and write it to the hard drive. I tried the following code:
baseencoder = new org.apache.commons.codec.binary.Base64();
url = new java.net.URL("https://server/file.tgz");
urlConnect = url.openConnection();
urlConnect.setDoInput(true);
urlConnect.setDoOutput(true);
urlConnect.setRequestProperty("authorization","Basic "+ java.lang.String(baseencoder.encodeBase64(java.lang.String( username + ":" + password ).getBytes())));
urlConnect.setRequestProperty("content-type","application/x-www-form-urlencoded");
is = new java.io.DataInputStream(urlConnect.getInputStream());
fstream = new FileWriter("C:\\tmp\\test.tgz");
out = new BufferedWriter(fstream);
while((data = is.read()) != -1){
out.write(data);
}
out.close();
is.close();
The resulting file is no longer a valid gzip archive. I'm sorry if I did a huge error but I'm not a programmer and don't know Java too much.
Don't use a FileWriter - that's trying to convert the data into text.
Just use FileOutputStream.
byte[] buffer = new byte[8 * 1024];
InputStream input = urlConnect.getInputStream();
try {
OutputStream output = new FileOutputStream(filename);
try {
int bytesRead;
while ((bytesRead = input.read(buffer)) != -1) {
output.write(buffer, 0, bytesRead);
}
} finally {
output.close();
}
} finally {
input.close();
}
I know this question is already answered, but a simpler approach is to use Apache Commons IO's IOUtils.copy() method, which can fully copy an InputStream to an OutputStream.
DataInputStream is meant for reading Java primitives, not for generic data.
It's also redundant, as urlConnect.getInputStream(); already returns an InputStream, and all InputStreams support read().
is = urlConnect.getInputStream();
P.S. This is assuming is and bis are the same variable. Otherwise, you're reading the wrong stream in the loop.
Just read about LimitInputStream sounds like it does exactly what you are doing, buffering the input stream for greater efficiency.
You can even use NIO FileChannel#transferFrom method.
URL website = new URL(urlToDownload);
try (ReadableByteChannel rbc = Channels.newChannel(website.openStream());
FileOutputStream fos = new FileOutputStream(filePath);) {
fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
}
Reference link1, link2

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