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Mysterious FileNotFoundException

I´m writing an Android app that communicates with a Tomcat Server running servlets. I´m doing a POST to the Tomcat server, specifying what file I want the server to send back to the client (the Android app). When I try to open this file by adding the file name sent with the POST to the catalog name I get a FileNotFoundException. But hardcoding exactly the same file name works just fine.
Copy pasting the file path obtained when the FileNotFoundException is thrown from the Tomcat servers console into windows explorer opens the correct file. I also wrote both the hardcoded file path, and the one where I append the file name to the catalog path, to a log file. In this log file both texts look exactly the same, and copy pasting both of them into windows explorer opens the correct file. Does anybody have an idea why this yields a FileNotFoundException?
Doing the post from client side
String potentialIP = "http://"+url+":8080/se.myPage/myServlet";
URL url = new URL(potentialIP);
conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("POST");
conn.setDoOutput(true);
conn.setChunkedStreamingMode(0);
// Starts the query
conn.connect();
OutputStream out = new BufferedOutputStream(conn.getOutputStream());
byte[] byteArray = korning.getBytes();
out.write(byteArray);
out.flush();
And the doPost method on the server side looks like this
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
InputStream in = request.getInputStream();
java.util.Scanner s = new java.util.Scanner(in).useDelimiter("\\A");
String fileName = s.hasNext() ? s.next() : "";
String filePath = "C:/myCatalog/"+fileName;
PrintWriter out = response.getWriter();
PrintWriter writer = new PrintWriter("C:/myCatalog/Servletlog.txt", "UTF-8");
writer.write("'"+"C:/myCatalog/hardCodedFileName.txt"+"'");
writer.write("'"+filePath+"'");
writer.flush();
writer.close();
BufferedReader reader = new BufferedReader(new FileReader(filePath));
String svar = reader.readLine();
reader.close();
out.close();
}
Anybody got an idea on how to solve this?

For me it turns out that the server was blocking whatever the default user agent is (maybe it was nothing) and was returning 403. And this throws the FileNotFoundException on my try. I then changed to an example json from another server: http://date.jsontest.com/
This will return a json that looks like this:
{
"time": "05:58:38 AM",
"milliseconds_since_epoch": 1400047118645,
"date": "05-14-2014"
}
By switching to another Server everything worked great - later I figured out that there is a problem with (as I said above) the user agent - set it to something like the Chrome user agent and it also should work normally.
Hope it will help you.

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.)

Download file from ftp server

i am writing a small android application which requires some data which is stored on my web server. The file is a .txt file curretly less than 1 MB. Is it advisable to set up a ftp server to get the data or can i just use a http get method to get the contents on a file. If i am using a http get can someone please tell me the java code required for this operation.

This is out of my head (so an error could have sneaked in):
URL url = new URL("http://www.yourserver.com/some/path");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
FileOutputStream out = new FileutputStream("/path/to/your/output/file");
byte[] buffer = new byte[16384];
int len;
while((len = in.read(buffer)) != -1){
out.write(buffer, 0, len);
}
finally {
urlConnection.disconnect();
}

Java and FTP to edit online text files

In my Java swing program, I read, edit and save various text files in a local folder using Scanner and BufferedWriter. Is there an easy way I can keep my current code, but, using FTP, edit a web file rather than a local file? Thanks everyone.

You can use the URL and URLConnection classes to obtain InputStreams and OutputStreams to files located on an FTP Server.
To read a file
URL url = new URL("ftp://user:pass#my.ftphost.com/myfile.txt");
InputStream in = url.openStream();
to write a file
URL url = new URL("ftp://user:pass#my.ftphost.com/myfile.txt");
URLConnection conn = url.openConnection();
conn.setDoOutput(true);
OutputStream out = conn.getOutputStream();

I tried to achieve the same and the answers to those questions helped me a lot:
Adding characters to beginning and end of InputStream in Java (the one marked as right shows how to add a custom string to the InputStream)
Uploading a file to a FTP server from android phone? (the one from Kumar Vivek Mitra shows how to upload a file)
I added new text to the end of my online file like this:
FTPClient con = null;
try {
con = new FTPClient();
con.connect(Hostname);
if (con.login(FTPUsername, FTPPassword)) {
con.enterLocalPassiveMode(); // important!
con.setFileType(FTP.BINARY_FILE_TYPE);
InputStream onlineDataIS = urlOfOnlineFile.openStream();
String end = "\nteeeeeeeeeeeeeeeeest";
List<InputStream> streams = Arrays.asList(
onlineDataIS,
new ByteArrayInputStream(end.getBytes()));
InputStream resultIS = new SequenceInputStream(Collections.enumeration(streams));
// Stores a file on the server using the given name and taking input from the given InputStream.
boolean result = con.storeFile(PathOfTargetFile, resultIS);
onlineDataIS.close();
resultIS.close();
if (result) Log.v("upload result", "succeeded");
con.logout();
con.disconnect();
}
return "Writing successful";
} catch (IOException e) {
// some smart error handling
}
Hope that helps.

URLConnection slow to call getOutputStream using an FTP url

I have this little piece of code below which uploads a file in java, the code functions correctly however it hangs for a long time when opening the output stream.
// open file to upload
InputStream filein = new FileInputStream("/path/to/file.txt");
// connect to server
URL url = new URL("ftp://user:pass#host/dir/file.txt");
URLConnection urlConn = url.openConnection();
urlConn.setDoOutput(true);
// write file
// HANGS FROM HERE
OutputStream ftpout = urlConn.getOutputStream();
// TO HERE for about 22 seconds
byte[] data = new byte[1024];
int len = 0;
while((len = filein.read(data)) > 0) {
ftpout.write(data,0, len);
}
// close file
filein .close();
ftpout.close();
In this example the URLConnection.getOutputStream() method hangs for about 22 seconds before continuing as normal, the file is successfully uploaded. The file is only 4 bytes in this case, just a text file with the word 'test' in it and the code hangs before the upload commences so its not because its taking time to upload the file.
This is only happening when connecting to one server, when I try a different server its as fast I could hope for which leads me to think it is a server configuration issue in which case this question may be more suited to server fault, however if I upload from an FTP client (in my case FileZilla) it works fine so it could be there is something I can do with the code to fix this.
Any ideas?

I have solved the problem by switching to use the Commons Net FTPClient which does not apear to have the same problems which changes the code to this below.
InputStream filein = new FileInputStream(new File("/path/to/file.txt"));
// create url
FTPClient ftp = new FTPClient();
ftp.connect(host);
ftp.login(user, pass);
int reply = ftp.getReplyCode();
if(!FTPReply.isPositiveCompletion(reply)) {
ftp.disconnect();
System.err.println("FTP server refused connection.");
return;
}
OutputStream ftpout = ftp.appendFileStream("text.txt");
// write file
byte[] data = new byte[1024];
int len = 0;
while((len = filein.read(data)) > 0) {
ftpout.write(data,0, len);
}
filein.close();
ftpout.close();
ftp.logout();