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• Java: opening and reading from a file without locking it.

  - by rogue780

  I need to be able to mimic 'tail -f' with Java. I'm trying to read a log file as it's being written by another process, but when I open the file to read it, it locks the file and the other process can't write to it anymore. Any help would be greatly appreciated! Here is the code that I'm using currently: public void read(){ Scanner fp = null; try{ fp = new Scanner(new FileReader(this.filename)); fp.useDelimiter("\n"); }catch(java.io.FileNotFoundException e){ System.out.println("java.io.FileNotFoundException e"); } while(true){ if(fp.hasNext()){ this.parse(fp.next()); } } }

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• Android bluetooth socket error

  - by ashwini

  I am using backport bluetooth api on android 1.6. I am using Google Bluetooth Chat sample app for testing. The app works fine in normal scenarios. In a scenario, when I try to connect to paired device which is in off state, I get following error. 01-04 09:00:11.629: ERROR/BluetoothEventLoop.cpp(84): onGetRemoteServiceChannelResult: D-Bus error: org.bluez.Error.ConnectionAttemptFailed (Host is down) 01-04 09:00:11.729: DEBUG/dalvikvm(128): GC freed 4535 objects / 256008 bytes in 296ms 01-04 09:00:21.880: ERROR/bluetooth_RfcommSocket.cpp(1433): connect error: Host is down (112) But it sets the state as connected. The app is unable to catch the exception. Why does it happen? Or is it the case with backport api? Any help is appreciated as I am struggling a lot to get things run fine.

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• Socket ping-pong performance

  - by Kamil_H

  I have written two simple programs (tried it in C++ and C#). This is pseudo code: -------- Client --------------- for(int i = 0; i < 200.000; i++) { socket_send("ping") socket_receive(buff) } --------- Server ------------- while(1) { socket_receive(buff) socket_send("pong") } I tried it on Windows. Execution time of client is about 45 seconds. Can somebody explain me why this takes so long? I understand that if there were real network connection between client and server the time of one 'ping-pong' would be: generate_ping + send_via_network + generate_pong + send_via_network but here everything is done in 'local' mode. Is there any way to make this inter process ping-pong faster using network sockets (I'm not asking about shared memory for example :) )

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• GAE and Socket Data

  - by Vinod

  I have a field device which keeps on sending data over to any designated port using sockets. I am planning to use GAE for server-side infrastructure. I read GAE does not support sockets. But i can configure the device to send the data over port 80. so we wrote a genericservlet to capture this data on GAE. But it is not obtaining any values from the client. any suggestions to fix this issue?

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• Detecting I/O errors in a NON BLOCKING SOCKET

  - by ripunjay-tripathi-gmail-com

  I am writing a client - server system in which I used NON-BLOCKING sockets. My problem is to detect error { while performing send() or write() } that may occur while data transfer. Example lets say, while the data is being transferred the peer crashes. Another case there is some network problem, something like wire unplugged etc. As of now, I am using a high level ACK, that peer sends after receiving the complete data. Ripunjay Tripathi

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• Buffer management for socket application best practice

  - by Poni

  Having a Windows IOCP app............ I understand that for async i/o operation (on network) the buffer must remain valid for the duration of the send/read operation. So for each connection I have one buffer for the reading. For sending I use buffers to which I copy the data to be sent. When the sending operation completes I release the buffer so it can be reused. So far it's nice and not of a big issue. What remains unclear is how do you guys do this? Another thing is that even when having things this way, I mean multi-buffers, the receiver side might be flooded (talking from experience) with data. Even setting SO_RCVBUF to 25MB didn't help in my testings. So what should I do? Have a to-be-sent queue?

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• Silverlight Socket Constantly Returns With Empty Buffer

  - by Benny

  I am using Silverlight to interact with a proxy application that I have developed but, without the proxy sending a message to the Silverlight application, it executes the receive completed handler with an empty buffer ('\0's). Is there something I'm doing wrong? It is causing a major memory leak. this._rawBuffer = new Byte[this.BUFFER_SIZE]; SocketAsyncEventArgs receiveArgs = new SocketAsyncEventArgs(); receiveArgs.SetBuffer(_rawBuffer, 0, _rawBuffer.Length); receiveArgs.Completed += new EventHandler<SocketAsyncEventArgs>(ReceiveComplete); this._client.ReceiveAsync(receiveArgs); if (args.SocketError == SocketError.Success && args.LastOperation == SocketAsyncOperation.Receive) { // Read the current bytes from the stream buffer int bytesRecieved = this._client.ReceiveBufferSize; // If there are bytes to process else the connection is lost if (bytesRecieved > 0) { try { //Find out what we just received string messagePart = UTF8Encoding.UTF8.GetString(_rawBuffer, 0, _rawBuffer.GetLength(0)); //Take out any trailing empty characters from the message messagePart = messagePart.Replace('\0'.ToString(), ""); //Concatenate our current message with any leftovers from previous receipts string fullMessage = _theRest + messagePart; int seperator; //While the index of the seperator (LINE_END defined & initiated as private member) while ((seperator = fullMessage.IndexOf((char)Messages.MessageSeperator.Terminator)) > 0) { //Pull out the first message available (up to the seperator index string message = fullMessage.Substring(0, seperator); //Queue up our new message _messageQueue.Enqueue(message); //Take out our line end character fullMessage = fullMessage.Remove(0, seperator + 1); } //Save whatever was NOT a full message to the private variable used to store the rest _theRest = fullMessage; //Empty the queue of messages if there are any while (this._messageQueue.Count > 0) { ... } } catch (Exception e) { throw e; } // Wait for a new message if (this._isClosing != true) Receive(); } } Thanks in advance.

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• method to find my UDP socket's "real" port?

  - by yairchu

  Is there any free service to which I could send a UDP packet and it would respond telling me what is my "real" UDP port? (my application is behind a NAT) This kind of service could allow me to make a p2p coordination server with normal php hosting. The p2p clients would know their UDP ports from this service They will then contact my server over HTTP (which is what regular web hosting allows) and tell it their port (and ip, which is normally supplied to cgi scripts) My server will give the clients the IP addresses and ports of the other clients.

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• C socket programming: client send() but server select() doesn't see it

  - by Fantastic Fourier

  Hey all, I have a server and a client running on two different machines where the client send()s but the server doesn't seem to receive the message. The server employs select() to monitor sockets for any incoming connections/messages. I can see that when the server accepts a new connection, it updates the fd_set array but always returns 0 despite the client send() messages. The connection is TCP and the machines are separated by like one router so dropping packets are highly unlikely. I have a feeling that it's not select() but perhaps send()/sendto() from client that may be the problem but I'm not sure how to go about localizing the problem area. while(1) { readset = info->read_set; ready = select(info->max_fd+1, &readset, NULL, NULL, &timeout); } above is the server side code where the server has a thread that runs select() indefinitely. rv = connect(sockfd, (struct sockaddr *) &server_address, sizeof(server_address)); printf("rv = %i\n", rv); if (rv < 0) { printf("MAIN: ERROR connect() %i: %s\n", errno, strerror(errno)); exit(1); } else printf("connected\n"); sleep(3); char * somemsg = "is this working yet?\0"; rv = send(sockfd, somemsg, sizeof(somemsg), NULL); if (rv < 0) printf("MAIN: ERROR send() %i: %s\n", errno, strerror(errno)); printf("MAIN: rv is %i\n", rv); rv = sendto(sockfd, somemsg, sizeof(somemsg), NULL, &server_address, sizeof(server_address)); if (rv < 0) printf("MAIN: ERROR sendto() %i: %s\n", errno, strerror(errno)); printf("MAIN: rv is %i\n", rv); and this is the client side where it connects and sends messages and returns connected MAIN: rv is 4 MAIN: rv is 4 any comments or insightful insights are appreciated.

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• How to deal with MySQL Connector/ODBC error "Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock'"

  - by user12653020

  I am sure many users run into a mysterious problem when perfectly working ODBC configurations started failing with errors like: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' The above error message might be preceded with something like [nxDc[yQ]. At the same time odbc.ini specifies in its DSN different SOCKET=/tmp/mysql.sock or a TCP connection SERVER=<remote_host_or_ip>. The question is, what had happened that the ODBC driver started to ignore the DSN options? The clue lies in the corrupted string [nxDc[yQ], which actually was [UnixODBC][MySQL] with each 2nd symbol removed. This is the case of bad conversion from SQLCHAR to SQLWCHAR. The UnixODBC driver manager took a single-byte character string from the client application and tried to convert it into the wide (multi-byte) characters for the Unicode version of MyODBC driver: Initially the piece of the connection string was represented by 1-byte chars like: [S][E][R][V][E][R][=][m][y][h][o][s][t][;] after the bad conversion to wide chars (commonly 2-byte UTF-16) [SE][RV][ER][=m][yh][os][t;] instead of [S\0][E\0][R\0][V\0][E\0][R\0][=\0][m\0][y\0][h\0][o\0][s\0][t\0][;\0] Naturally, the MyODBC driver could not parse the bad string and tried to use the default connection type (SOCKET) with the default value (/var/lib/mysql/mysql.sock) Now we know what happened, but why it happened? In most cases it happened because of using ODBCManageDataSourcesQ4 utility or its older analog ODBCConfig. When registering ODBC drivers they put lots of additional options and one of these options badly affects the UnixODBC driver manager itself. The solution is simple - remove or comment out the option in odbcinst.ini file (it is empty by default) set for the driver: [MySQL ODBC 5.2.6 Driver] Description    = Driver         = /home/dbs/myodbc526/lib/libmyodbc5w.so Driver64       = /home/dbs/myodbc526/lib/libmyodbc5w.so Setup          = /home/dbs/myodbc526/lib/libmyodbc5S.so Setup64        = /home/dbs/myodbc526/lib/libmyodbc5S.so UsageCount     = 1 CPTimeout      = 0 CPTimeToLive   = 0 IconvEncoding  =  # <--------- remove this line Trace          = TraceFile      = TraceLibrary   = After applying this simple solution (remove the line with IconvEncoding = ) everything came to normal. Prior to removing that line I tried putting different encoding names there, but the result was not good, so I really don't know how to properly use it. Unfortunately, UnixODBC manuals say nothing about it. Therefore, removing this option was the only way to get things done.

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• Boost Asio UDP retrieve last packet in socket buffer

  - by Alberto Toglia

  I have been messing around Boost Asio for some days now but I got stuck with this weird behavior. Please let me explain. Computer A is sending continuos udp packets every 500 ms to computer B, computer B desires to read A's packets with it own velocity but only wants A's last packet, obviously the most updated one. It has come to my attention that when I do a: mSocket.receive_from(boost::asio::buffer(mBuffer), mEndPoint); I can get OLD packets that were not processed (almost everytime). Does this make any sense? A friend of mine told me that sockets maintain a buffer of packets and therefore If I read with a lower frequency than the sender this could happen. ¡? So, the first question is how is it possible to receive the last packet and discard the ones I missed? Later I tried using the async example of the Boost documentation but found it did not do what I wanted. http://www.boost.org/doc/libs/1_36_0/doc/html/boost_asio/tutorial/tutdaytime6.html From what I could tell the async_receive_from should call the method "handle_receive" when a packet arrives, and that works for the first packet after the service was "run". If I wanted to keep listening the port I should call the async_receive_from again in the handle code. right? BUT what I found is that I start an infinite loop, it doesn't wait till the next packet, it just enters "handle_receive" again and again. I'm not doing a server application, a lot of things are going on (its a game), so my second question is, do I have to use threads to use the async receive method properly, is there some example with threads and async receive? Thanks for you attention.

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• socket programming: How do I handle out of band data

  - by soulmerge

  I just looked into wikipedia's entry on out-of-band data and as far as I understand, OOB data is somehow flagged more important and treated as ordinary data, but transmitted in a seperate stream, which profoundly confuses me. The actual question would be (besides "Could someone explain what OOB data is?"): I'm writing a unix application that uses sockets and need to make use of select() and was wondering what to do with the exceptfds parameter? Do I need to put all my sockets into this parameter and react to such events? Or do I just ignore them?

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• Ruby: Read large data from stdout and stderr of an external process on Windows

  - by BinaryMuse

  Greetings, all, I need to run a potentially long-running process from Ruby on Windows and subsequently capture and parse the data from the external process's standard output and error. A large amount of data can be sent to each, but I am only necessarily interested in one line at a time (not capturing and storing the whole of the output). After a bit of research, I found that the Open3 class would take care of executing the process and giving me IO objects connected to the process's standard output and error (via popen3). Open3.popen3("external-program.bat") do |stdin, out, err, thread| # Step3.profit() ? end However, I'm not sure how to continually read from both streams without blocking the program. Since calling IO#readlines on out or err when a lot of data has been sent results in a memory allocation error, I'm trying to continuously check both streams for available input, but not having much luck with any of my implementations. Thanks in advance for any advice!

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• buffer size for socket connection in c++

  - by wyatt

  I'm trying to build a basic POP3 mail client in C/++, but I've run into a bit of an issue. Since you have to define the buffer size when building the program, but a message can be arbitrarily large, how do you, say, get the mail server to send it to you in parts? And if this isn't the correct means of solving the problem, what is? And while I'm here, can anyone confirm for me that RFC 2822 is still the current document defining email layout? Thanks

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• How do I detect server status in a port scanner java implementation

  - by akz

  I am writing a port scanner in Java and I want to be able to distinct the following 4 use cases: port is open port is open and server banner was read port is closed server is not live I have the following code: InetAddress address = InetAddress.getByName("google.com"); int[] ports = new int[]{21, 22, 23, 80, 443}; for (int i = 0; i < ports.length; i++) { int port = ports[i]; Socket socket = null; try { socket = new Socket(address, port); socket.setSoTimeout(500); System.out.println("port " + port + " open"); BufferedReader reader = new BufferedReader( new InputStreamReader(socket.getInputStream())); String line = reader.readLine(); if (line != null) { System.out.println(line); } socket.close(); } catch (SocketTimeoutException ex) { // port was open but nothing was read from input stream ex.printStackTrace(); } catch (ConnectException ex) { // port is closed ex.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { if (socket != null && !socket.isClosed()) { try { socket.close(); } catch (Exception e) { e.printStackTrace(); } } } } The problem is that I get a ConnectionException both when the port is closed and the server cannot be reached but with a different exception message: java.net.ConnectException: Connection timed out: connect when the connection was never established and java.net.ConnectException: Connection refused: connect when the port was closed so I cannot make the distinction between the two use cases without digging into the actual exception message. Same thing happens when I try a different approach for the socket creation. If I use: socket = new Socket(); socket.setSoTimeout(500); socket.connect(new InetSocketAddress(address, port), 1000); I have the same problem but with the SocketTimeoutException instead. I get a java.net.SocketTimeoutException: Read timed out if port was open but there was no banner to be read and java.net.SocketTimeoutException: connect timed out if server is not live or port is closed. Any ideas? Thanks in advance!

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• In Java how do a read an input stream in to a string?

  - by Johnny Maelstrom

  If you have an java.io.InputStream object how should you process that object and produce a string.

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• breaking out from socket select

  - by kamziro

  I have a loop which basically calls this every few seconds (after the timeout): while(true){ if(finished) return; switch(select(FD_SETSIZE, &readfds, 0, 0, &tv)){ case SOCKET_ERROR : report bad stuff etc; return; default : break; } // do stuff with the incoming connection } So basically for every few seconds (which is specified by tv), it reactivates the listening. This is run on thread B (not a main thread). There are times when I want to end this acceptor loop immediately from thread A (main thread), but seems like I have to wait until the time interval finishes.. Is there a way to disrupt the select function from another thread so thread B can quit instantly?

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• Terminate an inactive socket connection from TIdTCPServer

  - by A.J.

  We have an application which listens for incoming TCP requests using the Indy 10.1.1 components that ship with Delphi 2007. Occassionally we receive incoming connections which are not from our client application. Typically, one of two things happens: 1) the connection is terminated by the client before any data is received, or 2) data is received which we're not expecting and we manually terminate the connection. However, we've received connections where no data is received and appear to persist until the client terminates the connection from their end. Is there a way to terminate such a connection from the server if no data is received after a specified amount of time?

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• Hard drive write speed - finding a lighter antivirus?

  - by Shingetsu

  I recently have been getting a lot of system lag here (for example, the mouse and the display in general take about 15 seconds to react in the worst cases). After a lot of monitoring the resources, I found that the problem mainly happens when too much Disk I/O is being done. Three culprits have been identified: My browser had the highest write I/O with 35,000,000 I/O Write Bytes. Steam had the highest read I/O (when IDLE!!!) with 106,000,000 I/O Read Bytes. My antivirus (in both cases I will soon mention) was the runner up in both cases with: 30,000,000ish write and 80,000,000ish read. The first AV I had was Avast! which I had liked on my previous system. After noticing it taking so much I/O I switched to Panda (supposing it wouldn't use TOO much during idle phase). However it only used a bit less I/O. Just a lot less memory and cpu and somewhat more network. My browser at the moment is Maxthon 3 (which I like a lot). Before this I was running chrome which had similar data and much higher cpu when running in the background was enabled. I'm not going to be running steam all the time and there aren't many alternatives to it. I like my browser very much, but I AM willing to switch if there's an obvious problem (I'm in programming, however I'm not a very good sysadmin, especially not when it comes to windows). Finally, my system almost stops lagging when I turn off the antivirus (and preferably steam) (some remains but once in every 5-6 hours for a few seconds so it isn't a big problem). My question (has a few parts): Is it possible to configure steam to lower it's I/O usage? (and maybe network while we're at it?) Which antivirus (very preferably free) uses lowest I/O while idle (I leave PC alone during active scans so that isn't a problem). Is there an obvious problem with my current browser and, if so, is there a way to fix it or should I switch and, if so, to what? (P.S. I've been on FFox for some time too). Info on system: Windows 7 (32 bit T_T, I am getting a new one in a few months but I want to keep using system during that time though). Hard Drive (main) is a Raid0. (Also have an external 1TB one which contains steam (and steam alone). As such it doesn't get used by much anything other than steam and isn't a very large problem. However steam still uses some I/O of registry) CPU: Intel(R) Core(TM)2 CPU [email protected] RAM: 6GB (3.25GB usable) (this and CPU have little effect as shown in next section) Additional info: Memory usage during problematic times: 44% CPU usage during problematic times: 35% Page File: main drive: system managed. 1TB drive: none. The current system I'm using is about 6 years old and is mainly a place holder while I await the new one in a few months. Final words: this is my 1st post on Super User (this question wouldn't feel right on Stack Overflow where I usually stay). If it doesn't have it's place here please tell me. If anything is wrong with it, same. Edit Technically I'm looking for a live thread detection program with minimal IO usage. I already have good active scan capability: Kaspersky (the free scanner uses the paid database) and MalwareBytes. Edit 2 Noticed another one, it seems that windows media player has been using stuff even when off! Turning it off and restarting now. If the problem is fixed I'll tell you guys. The reason I didn't notice it before was because I didn't have resource manager in front of me at the MOMENT of the problem. Now I did and it was at the very top of the list!

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• programs hangs during socket interaction

  - by herrturtur

  I have two programs, sendfile.py and recvfile.py that are supposed to interact to send a file across the network. They communicate over TCP sockets. The communication is supposed to go something like this: sender =====filename=====> receiver sender <===== 'ok' ======= receiver or sender <===== 'no' ======= receiver if ok: sender ====== file ======> receiver I've got The sender and receiver code is here: Sender: import sys from jmm_sockets import * if len(sys.argv) != 4: print "Usage:", sys.argv[0], "<host> <port> <filename>" sys.exit(1) s = getClientSocket(sys.argv[1], int(sys.argv[2])) try: f = open(sys.argv[3]) except IOError, msg: print "couldn't open file" sys.exit(1) # send filename s.send(sys.argv[3]) # receive 'ok' buffer = None response = str() while 1: buffer = s.recv(1) if buffer == '': break else: response = response + buffer if response == 'ok': print 'receiver acknowledged receipt of filename' # send file s.send(f.read()) elif response == 'no': print "receiver doesn't want the file" # cleanup f.close() s.close() Receiver: from jmm_sockets import * s = getServerSocket(None, 16001) conn, addr = s.accept() buffer = None filename = str() # receive filename while 1: buffer = conn.recv(1) if buffer == '': break else: filename = filename + buffer print "sender wants to send", filename, "is that ok?" user_choice = raw_input("ok/no: ") if user_choice == 'ok': # send ok conn.send('ok') #receive file data = str() while 1: buffer = conn.recv(1) if buffer=='': break else: data = data + buffer print data else: conn.send('no') conn.close() I'm sure I'm missing something here in the sorts of a deadlock, but don't know what it is.

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• XML RPC client for C# over secured socket (https)

  - by Ummar

  I have a secured (https) XML-RPC server written in python, and I have tested it with a python based client. but I need a C# based client for it, I have given a try to xml-rpc.net but it is not working with https? can any one please help me out? or I will have to write a client from scratch? Thanks

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• python send/receive hex data via TCP socket

  - by Mike

  I have a ethenet access control device that is said to be able to communicate via TCP. How can i send a pachet by entering the HEX data, since this is what i have from their manual (a standard format for the communication packets sent and received after each command)

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• Migrating Ajax web application to web socket

  - by Bastan

  Hi, I think i'm just missing a little detail that is preventing me from seeing the whole picture. I have a web application which use ajax request every x time to update client with new information or tasks. I also have a long running process on the server which is a java computation engine. I would like this engine to send update to the client. I am wondering how to migrate my web app to using websocket. Probably phpwebsocket or similar. Can my server 'decide' to send information to a specific client? It seems possible looking at the php-websocket. Can my java backend long process use the websocket server to send notification to a specific client. How? well I can say that my java app could use a class that could send over websocket instead of http. But how the websocket server knows to which client to send the 'info'. I am puzzle by all this. Any document that explain this in more details? It seems that the websocket could create an instance of my web application. Thanks

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• Send serialised object via socket

  - by RubbleFord

  Whats the best way to format a message to a server, at moment I'm serilising an object using the binaryformatter and then sending it to the server. At the server end its listening in an async fashion and then when the buffer size recieved is not 100% it assumes that the transfer has complete. This is working and the moment, and I can deserialise the object at the other end, I'm just concerned that if I start sending async this method will fail has message's could be blurred. I know that I need to mark the message somehow as to say that's the end of message one, this other bit belongs to message 2, but I'm unsure of the correct way to do this. Could anyone point me in the right direction and maybe give me some examples? Thanks

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• How to close IOs?

  - by blackdog

  when i managed IO, i found a problem. i used to close it like this: try { // my code } catch (Exception e) { // my code } finally{ if (is != null) { is.close(); } } but the close method also would throw exception. if i have more than one IO, i have to close all of them. so the code maybe like this: try { // my code } catch (Exception e) { // my code } finally{ if (is1 != null) { is1.close(); } if(is2 != null{ is2.close(); } // many IOs } if is1.close() throws an exception, is2, is3 would not close itself. So i have to type many try-catch-finally to control them. is there other way to solve the problem?

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