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Java Forum / General / September 2007PrintWriter woes
I create a PrintWriter with: p = new PrintWriter( new BufferedWriter(new OutputStreamWriter( mystream,"UTF-8"),4096)); and capture the bytes in the write method of mystream that extends OutputStream when I p.print(somestring) a number of times it pushes the bytes to mystream in 8192 chunks. How come when I've set BufferWriter to 4096? > when I p.print(somestring) a number of times it pushes the bytes to mystream > in 8192 chunks. How come when I've set BufferWriter to 4096? A character has a length of 2 bytes. It's not very clear what the API means with the size of the buffer but I assume it's characters. But to make sure you should look into the sources. Maybe there's another buffer (e.g. in OutputStreamWriter) leading to the effect. Regards, Lothar  SignatureLothar Kimmeringer E-Mail: spamfang@kimmeringer.de PGP-encrypted mails preferred (Key-ID: 0x8BC3CD81) Always remember: The answer is forty-two, there can only be wrong questions! >> when I p.print(somestring) a number of times it pushes the bytes to >> mystream [quoted text clipped - 7 lines] > > Regards, Lothar It doesn't matter what size is given to BufferedWriter it still sends buffers of 8192. Does sun.nio.cs.StreamEncoder buffer? And where is it? On Sun, 02 Sep 2007 00:34:54 GMT, "Crouchez" <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly quoted someone who said : >It doesn't matter what size is given to BufferedWriter it still sends >buffers of 8192. D How did you discover this? SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > It doesn't matter what size is given to BufferedWriter it still sends > buffers of 8192. Can you post the source you wrote for testing this? With the constructor Roedy was showing I would expect the number of bytes being sent to the underlying stream is dependent on the characters being written and the encoding to be used. With x characters written and UTF-8 used as encoding the number of bytes should vary between x (ASCII) and 3x (0x800 - 0xffff). So with a buffer-size of 4096 the number of bytes in your example could reach up to 12288. I don't know how OutputStreamWriter works internally but if there is a buffer as well this might be the reason, why you always get the same number of bytes. But I'm not going to look into that further until you posted your test-code. > Does sun.nio.cs.StreamEncoder buffer? And where is it? In rt.jar or charset.jar, but I would expect it in the first one. Regards, Lothar SignatureLothar Kimmeringer E-Mail: spamfang@kimmeringer.de PGP-encrypted mails preferred (Key-ID: 0x8BC3CD81) Always remember: The answer is forty-two, there can only be wrong questions! On Sat, 01 Sep 2007 20:58:43 GMT, "Crouchez" <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly quoted someone who said : >I create a PrintWriter with: >p = new PrintWriter( [quoted text clipped - 6 lines] >when I p.print(somestring) a number of times it pushes the bytes to mystream >in 8192 chunks. How come when I've set BufferWriter to 4096? look at the code for the BufferedWriter constructor. public BufferedWriter(Writer out, int sz) { super(out); if (sz <= 0) throw new IllegalArgumentException("Buffer size <= 0"); this.out = out; cb = new char[sz]; The size of the buffer is specified in chars. See http://mindprod.com/applet/fileio.html When it generates code for you it now documents the unit of measure for buffer sizes. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Sat, 01 Sep 2007 20:58:43 GMT, "Crouchez" <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly quoted someone who said : >when I p.print(somestring) a number of times it pushes the bytes to mystream >in 8192 chunks. How come when I've set BufferWriter to 4096? In short BufferedWriter constructor takes the size in chars. 4096 chars = 8192 bytes. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > On Sat, 01 Sep 2007 20:58:43 GMT, "Crouchez" > <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly [quoted text clipped - 6 lines] > In short BufferedWriter constructor takes the size in chars. 4096 > chars = 8192 bytes. It doesn't matter if you put a buffer of 1024 it still pushes a buffer through of 8192 out = new AnOutputStream( 1024); //buf then set as 1024 p = new PrintWriter( new BufferedWriter(new OutputStreamWriter( out,"UTF-8"),1024)); p.print(string) x 4000 times eg. result of public synchronized void write(byte b[], int off, int len) in out len:8192 ... > out = new AnOutputStream( 1024); //buf then set as 1024 > p = new PrintWriter( > new BufferedWriter(new OutputStreamWriter( > out,"UTF-8"),1024)); > > len:8192 > when I p.print(somestring) a number of times it pushes the bytes to mystream a.k.a. "out" > in 8192 chunks. How come when I've set BufferWriter to 4096? To be clear - you are seeing writes to the underlying stream in 8 KiB chunks? You aren't measuring the writes in either of the Writers? Had you considered reading the API docs for OutputStreamWriter? <http://java.sun.com/javase/6/docs/api/java/io/OutputStreamWriter.html> wherein it lets you know that: > Each invocation of a write() method causes the encoding converter to be invoked on the given character(s). > The resulting bytes are accumulated in a buffer before being written to the underlying output stream. The size of this buffer may be specified, but by default it is large enough for most purposes. Dollars to doughnuts the size of that OutputStreamWriter buffer on your system is 8 KiB. Any takers? Aren't the API docs wonderful? SignatureLew >> out = new AnOutputStream( 1024); //buf then set as 1024 >> p = new PrintWriter( [quoted text clipped - 24 lines] > > Aren't the API docs wonderful? So you can't set this value unless you create your own version of it? So sun.nio.cs.StreamEncoder buffers at 8192 potentially causing buffer overflows at the end of the line? "The size of this buffer may be specified, but by default it is large enough for most purposes. " Specified where exactly? "Lew" <lew@lewscanon.com> wrote in message >> Aren't the API docs wonderful? > So you can't set this value unless you create your own version of it? So > sun.nio.cs.StreamEncoder buffers at 8192 potentially causing buffer I'm not sure that's the class defining the buffer. How are you determining that it is? > overflows at the end of the line? There should be no risk of buffer overflow. > "The size of this buffer may be specified, but by default it is large enough > for most purposes. " > > Specified where exactly? Sometimes the API docs are not so wonderful. There is no apparent method or constructor to set the value. Regardless, you can always get the buffer to flush by calling flush(), so you don't need to worry about crud being caught in the buffer. Just put a finally { p.flush(); } in the right place, and you should be fine. Where the API docs are not so wonderful is in the documentation of these Writers' buffer strategies, although we've seen that they at least document that they have them. It makes it hard on us programmers to account for multiple buffers and the concomitant inefficiencies. Unless the Writers in question are smart enough to share their buffers? I don't know - I am far too lazy to read through the publicly available source code to find out for myself. I do know that one can at least make sure, as you've done, that there are at least some buffers. Your BufferedWriter of size 4096 will hold 8192 bytes in its buffer, apparently a good match for the default (and ineluctable) OutputStreamWriter buffer. Finish with a flush() and all should be well. SignatureLew On Sun, 02 Sep 2007 18:11:14 GMT, "Crouchez" <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly quoted someone who said : >It doesn't matter if you put a buffer of 1024 it still pushes a buffer >through of 8192 Again, how do you know this? SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Sat, 01 Sep 2007 20:58:43 GMT, "Crouchez" <blah@bllllllahblllbllahblahblahhh.com> wrote, quoted or indirectly quoted someone who said : >I create a PrintWriter with: >p = new PrintWriter( > new BufferedWriter(new OutputStreamWriter( > mystream,"UTF-8"),4096)); OutputStreamWriter extends Writer which has a 1024 char buffer. StreamEncoder has a default buffer of 8096 bytes. These buffers cascade, so like a multistage colon would act like a larger buffer. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com Free MagazinesGet these publications absolutely FREE for up to 12 months. 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