Java socket....
in [Java Programming]
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From: Felce e Mirtillo on 19 Apr 2010 06:10 Hi all, I'm writing an application to interface a device ( industrial balance ) to a PC via TCP/IP... well the device acts as Server and my application is a listening client. Th client receive a single string <stx>dd/mm/yyyy;hh:mm;0000000000;A;0000000000<etx> that I read with... a method like this: .... byte[] buffer = new byte[100]; int count = 0, offset = 0; count = socket.getInputStream().read(); while (count > 0 && count != 3) { buffer[offset++] = count; count = socket.getInputStream().read(); } String line = new String(buffer, 1, offset); String[] dati = new String[5] offset = 0; for(StringTokenizer t = new StringTokenizer(line, ";"); t.hasMoreTokens();) dati[offset++] = t.nextToken(); .... well the method is in a loop where I'd would trap some events. The most important is... if someone swich off the device and then switch off... the previous method remain 'blocked' waiting the next byte ... I've tryed several Socket methods.. but no one of them is usefull in order to intercept the death of tcp/ip connection... What can I do... ??? Any Idea ??? Thanks in advance... Dario (I apologize for my poor english.. I hope it is better than your average italian :P :P )
From: Roedy Green on 20 Apr 2010 06:39 On Mon, 19 Apr 2010 12:10:10 +0200, Felce e Mirtillo <dario.fantoni(a)gmail.com> wrote, quoted or indirectly quoted someone who said : >count = socket.getInputStream().read(); >while (count > 0 && count != 3) { you are going two layers lower protocol layer than you need. See http://mindprod.com/jgloss/http.html -- Roedy Green Canadian Mind Products http://mindprod.com It�s amazing how much structure natural languages have when you consider who speaks them and how they evolved.
From: Mike Amling on 20 Apr 2010 08:38 EJP wrote: > On 20/04/2010 12:13 AM, Mike Amling wrote: >> >> You need some kind of ping to make sure the device. > > No you don't, you just need a read timeout. Socket.setSoTimeout(). A read timeout does not distinguish between a dead device and a healthy device that has nothing to say. --Mike Amling
From: Mike Amling on 19 Apr 2010 10:13 Felce e Mirtillo wrote: > Hi all, > > I'm writing an application to interface a device ( industrial balance ) > to a PC via TCP/IP... well the device acts as Server and my application > is a listening client. > > Th client receive a single string > <stx>dd/mm/yyyy;hh:mm;0000000000;A;0000000000<etx> > that I read with... a method like this: > > ... > byte[] buffer = new byte[100]; > int count = 0, offset = 0; > > count = socket.getInputStream().read(); > while (count > 0 && count != 3) { > buffer[offset++] = count; > count = socket.getInputStream().read(); > } > String line = new String(buffer, 1, offset); > String[] dati = new String[5] > offset = 0; > for(StringTokenizer t = new StringTokenizer(line, ";"); > t.hasMoreTokens();) dati[offset++] = t.nextToken(); > ... > > well the method is in a loop where I'd would trap > some events. The most important is... if someone > swich off the device and then switch off... the > previous method remain 'blocked' waiting the next > byte ... > I've tryed several Socket methods.. but no one of > them is usefull in order to intercept the death > of tcp/ip connection... > > What can I do... ??? > Any Idea ??? > Thanks in advance... You need some kind of ping to make sure the device. When the device is turned off, all the control blocks for the TCP connection on the machine running Java remain valid. If no packets are being exchanged, there's no indication that anything is wrong. Is there a harmless message you could send to the device that would have no side effects? If so, send it every once in a while from a second Thread, and after the device is off, you should get an I/O error on the send, which will probably cause your blocked read to get either end-of-file or an I/O error. There's also a Socket.setKeepAlive(true), but I don't know exactly what it's defined to do. --Mike Amling
From: Mike Amling on 19 Apr 2010 10:19
Mike Amling wrote: > > You need some kind of ping to make sure the device. ...to make sure the device is still running. |