How can I write to remote file in server? I try this but I can´t
try {
BufferedWriter out = new BufferedWriter(new FileWriter("http://myserver/file.txt"));
out.write("Hello");
out.close();
} catch (IOException e) {
//handle exception
}
You can use the FTP library from Apache to get the file in to your local, modify it, then ftp it back.
2nd option, if you don't want to do heavy text modifying is to use sshExec. It lets you run commands on the server you connect to.
3rd option, execute the class on the server that the txt file exists.
Related
I'm trying to create a simple Client-Server java program. Simple, I need to send a text file (ToSend.txt) from the Server to the client, it's in the same directory where the Server.java is. After running the program, the ToSend.txt file should be in the same directory where the Client.java is, and will be renamed as Received.txt.
Server:
File file = new File("ToSend.txt");
try
{
ServerSocket serverSocket = new ServerSocket(1234);
Socket serverEndpoint = serverSocket.accept();
//what to do here?
serverEndpoint.close();
}
catch (Exception e)
{
e.printStackTrace();
}
Client:
try
{
Socket clientEndpoint = new Socket(localhost, 1234);
//what to do here?
clientEndpoint.close();
}
catch (Exception e)
{
e.printStackTrace();
}
ToSend.txt
Self-learning during a global pandemic is difficult.
I got confused if I will use DataOutputStream or just OutputStream or FileReader, i need help.
First you need to serialize the file then send it, you can't just send a file like that, this has been already answered, so I will not repeat the answer, I will just link an answer other user provided.
Java sending and receiving file (byte[]) over sockets
Try looking up videos how to serialize data in java there are different methods, using bytes like the one linked, this is part of the Java streams tutorial and it is very useful to learn how streams actually operate.
I use sauronsoftware.ftp4j.FTPClient to do scheduled file downloads from FTP servers.
My problem is that FTP server suddenly dies while the client downloads a file from it.
This is what i do:
for (FTPFile remoteFile : remoteFiles) {
String remoteFileName = remoteFile.getName();
String localPath = ftpDir.getLocalPath() + remoteFileName;
log.debug("Downloading remote file {} to local path {}", remoteFileName, localPath);
try {
client.download(remoteFileName, new File(localPath));
if (!ftpDir.isLeaveFilesOnServer()) {
//Delete remote file
client.deleteFile(remoteFileName);
}
} catch (IllegalStateException e) {
log.error("FTPException ",e);
fcr.addErrorFile(remoteFileName);
} catch (IOException e) {
log.error("FTPException ",e);
The problem is that download(...) runs by separate thread and when FTP server dies this thread continues to run anyway like forever. Is there a way to come around this problem or should i use another FTP client that can handle cases like this?
I'm not sure if your problem is your FTP connection dies sudden and unexpedtecly, or if the problem is the main thread finished its execution before files are downloaded. If we are talking about the second scenario, then maybe you can use this other method of the same FTPClient class:
public void download(java.lang.String remoteFileName,
java.io.File localFile,
FTPDataTransferListener listener)
and then make the main thread to wait until all downloads have finished before ending
When I am going to connect device through USB port, I want to detect it immediately.
I am searching for a Java API, my main target is Linux OS.
Does anyone know an API like that?
You can do something like this:
try {
String command = "lsusb"; // you may add some param if you want
// or use adb for instance
Process child = Runtime.getRuntime().exec(command);
// Get output stream to write from it
OutputStream out = child.getOutputStream();
// TODO parsing lsusb output
out.close();
} catch (IOException e) {
}
would also consider monitoring USB events by DBus interface
there is DBus-Java library here
and a similar thread but on python here
I have a list of feeds in a database that I use to download a XML file from a FTP server and then parse it. The scrpt is bundled up into a jar file which is run daily using Windows Task Scheduler. Occasionally the request get haulted at grabbing a certain xml file. So far it has happened about 3 times in 2 weeks with no real pattern that I can see.
When it does mess up, I go to the computer it is being run from, I see the command window open and it is stopped before the xml has been fully downloaded. If I close the command window and run the task manually everything will work fine.
The code that I am using to download the xml file is:
private void loadFTPFile(String host, String username, String password, String filename, String localFilename){
System.out.println(localFilename);
FTPClient client = new FTPClient();
FileOutputStream fos = null;
try {
client.connect(host);
client.login(username, password);
String localFilenameOutput = createFile(assetsPath + localFilename);
fos = new FileOutputStream(localFilenameOutput);
client.retrieveFile(filename, fos);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (fos != null)
fos.close();
client.disconnect();
} catch (IOException e) {
e.printStackTrace();
}
}
}
This function is being called in a loop and when it fails, everything stops and the script doesn't go onto the next feed.
I'm not sure what is happening, possibly the connection being lost, but I would think that the try/catch would catch if that is happening. I'm not sure if a timeout would do the trick or threads need to be used (but I've never worked with threads)
Could anyone point me in the right direction onto why this is happening and what I can do to fix the problem
UPDATE - Set a timeout for the data connection
Since the last file is only partially downloaded, and given the source of FTPClient.retrieveFile(), I think it may be a problem on the server side (something that make it hang, or even die - who knows). Obviously one can't repair the server or even know what's going on there, anyway I suggest to add a timeout with setDataTimeout(int) and catch the possible SocketTimeoutException separately to be logged in a different place and maybe sent to the FTP server admins (along with the time information when it happened) so they can merge the logs and see what's the issue.
OLD ANSWER
I didn't notice that you connect and login for each and every file, so the following is just an optimization not to close the control connection and succesfully logout, but it should not address the problem.
You could start the JVM in debug mode and attach a debugger when it hangs, anyway according to this answer and this thread it can be a timeout problem on the network equipment devices (routers). From the FTPClient Javadoc
During file transfers, the data connection is busy, but the control
connection is idle. FTP servers know that the control connection is in
use, so won't close it through lack of activity, but it's a lot harder
for network routers to know that the control and data connections are
associated with each other. Some routers may treat the control
connection as idle, and disconnect it if the transfer over the data
connection takes longer than the allowable idle time for the router.
One solution to this is to send a safe command (i.e. NOOP) over the control connection to reset the router's idle timer. This is enabled as follows:
ftpClient.setControlKeepAliveTimeout(300); // set timeout to 5 minutes
Do you check the return status of any of the calls or is that the code?
There is a call completePendingCommand() that has to be used on occassion. That may be something to look into.
Also, you won't see an IO exception, I belive it gets repackaged as a CopyStreamException
You might want to also change the return value to a boolean since you trap the exceptions, at least the calling loop will know whether the tranfer happened or not.
private boolean loadFTPFile(String host, String username, String password, String filename, String localFilename){
System.out.println(localFilename);
FTPClient client = new FTPClient();
FileOutputStream fos = null;
try {
client.connect(host);
int reply = client.getReplyCode();
if (!FTPReply.isPositiveCompletion(reply)){
client.disconnect();
System.err.println("FTP server refused connection.");
return false;
}
if (!client.login(username, password)){
client.logout();
return false;
}
String localFilenameOutput = createFile(assetsPath + localFilename);
fos = new FileOutputStream(localFilenameOutput);
boolean result = client.retrieveFile(filename, fos);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
if (result){
System.out.println("\tFile Transfer Completed Successfully at: " + sdf.format(Calendar.getInstance().getTime()));
// ftp.completePendingCommand();
}
else {
System.out.println("\tFile Transfer Failed at: " + sdf.format(Calendar.getInstance().getTime()));
}
return result;
}catch (CopyStreamException cse){
System.err.println("\n\tFile Transfer Failed at: " + sdf.format(Calendar.getInstance().getTime()));
System.err.println("Error Occurred Retrieving File from Remote System, aborting...\n");
cse.printStackTrace(System.err);
System.err.println("\n\nIOException Stack Trace that Caused the Error:\n");
cse.getIOException().printStackTrace(System.err);
return false;
}catch (Exception e){
System.err.println("\tFile Transfer Failed at: " + sdf.format(Calendar.getInstance().getTime()));
System.out.println("Error Occurred Retrieving File from Remote System, aborting...");
e.printStackTrace(System.err);
return false;
} finally {
try {
if (fos != null)
fos.close();
client.disconnect();
} catch (IOException e) {
e.printStackTrace();
}
}
}
It's not a threading issue. Chances are it is caused by something in the loop since that code looks like it should clean up just fine. That said, for testing you will probably want to add
catch (Exception e) {
e.printStackTrace();
}
after the IOException catch clause. It's possible that another exception is being thrown.
Another thing, if you are pulling results from the database result set one at a time and doing the FTP gets, that might be a problem. Unless the results are all brought back by the JDBC call at once, that too could time out. Not all database queries actually return the entire result set to the client at once.
For some reason when I connect one Java client to my Cpp server it works perfectly. But when another Java applet tries to connect in addition to the first, it does but it stops receiving data from the server. Some of the other attempts would completly freeze the applet. I have searched everywhere on the 'net but found nothing. I would appreciate any help on the subject like advice, links or source. My only other option (since Flash is out of the question) is to use Active X, but then I would lose all my crossplatform-ability :(. My source (minus debugging code and so on) follows.
public void init() {
try {
socket = new Socket("localhost",4000);
} catch (UnknownHostException e) {
System.out.println("Unknown host");
} catch (IOException e) {
System.out.println("IO Exception");
return;
}
BufferedReader fromServer = null;
PrintWriter toServer = null;
fromServer = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
toServer =
new PrintWriter(socket.getOutputStream(), true);
toServer.flush();
It sounds like your Cpp server can't handle multiple connections. Can you verify that you can accept more than one incoming network connection?
I found the solution! You can't run multiple applets in one browser and one machine. It will work if you load them in seperate browsers (like IE and FF) or load it on a seperate machine (like remotely). I hope this helps.