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Java Forum / General / November 2006File /dev/null in Java ?
Hi, is there a garbage file in Java like /dev/null in UNIX? I want temporarily throw away System.out outputs. PrintStream out_orig=System.out; System.setOut(new PrintStream(new File("trash.txt"))); ... System.setOut(out_orig); The file "trash.txt" is created always, but I don't need it (and don't want it). What could I do? Juergen > is there a garbage file in Java like /dev/null in UNIX? > I want temporarily throw away System.out outputs. [quoted text clipped - 6 lines] > The file "trash.txt" is created always, but I don't need it (and > don't want it). What could I do? You could subclass PrintStream with methods that do nothing. It may be enough to override its three write methods: public class NullPrintStream extends PrintStream { void write(byte[] buf, int off, int len) {} void write(int b) {} void write(byte [] b) {} } Then just: System.setOut(new NullPrintStream()); I'm not sure, but this is how I would start. > > is there a garbage file in Java like /dev/null in UNIX? > > I want temporarily throw away System.out outputs. [quoted text clipped - 15 lines] > void write(byte [] b) {} > } Good but better would be to subclass OutputStream. It would be sufficient to write one write method. Then you could use it as an argument to the PrintStream constructor System . setOut ( new java . io . PrintStream ( new java . io . OutputStream ( ) { public void write ( int b ) { } } ) ) ; > Then just: > > System.setOut(new NullPrintStream()); > > I'm not sure, but this is how I would start. >>> is there a garbage file in Java like /dev/null in UNIX? >>> I want temporarily throw away System.out outputs. ... >> You could subclass PrintStream with methods that do nothing. It may be >> enough to override its three write methods: [quoted text clipped - 11 lines] > System . setOut ( new java . io . PrintStream ( new java . io . > OutputStream ( ) { public void write ( int b ) { } } ) ) ; Nice. That may be the solution. > System . setOut ( new java . io . PrintStream ( new java . io . > OutputStream ( ) { public void write ( int b ) { } } ) ) ; This works greatly. Thank you! Juergen J?rgen Gerstacker wrote: > > System . setOut ( new java . io . PrintStream ( new java . io . > > OutputStream ( ) { public void write ( int b ) { } } ) ) ; > > This works greatly. Thank you! > Juergen Bitte! > Hi, > is there a garbage file in Java like /dev/null in UNIX? [quoted text clipped - 7 lines] > The file "trash.txt" is created always, but I don't need it (and don't > want it). What could I do? Did you try this? System.setOut(null); I believe I did that a long time ago, and it seemed to work (silenced the output, didn't throw null pointer exceptions). - Oliver >> is there a garbage file in Java like /dev/null in UNIX? >> I want temporarily throw away System.out outputs. ... > Did you try this? > > System.setOut(null); > > I believe I did that a long time ago, and it seemed to work > (silenced the output, didn't throw null pointer exceptions). The main problem I would have with that is that the docs do not say anything about it - I just looked up System.setOut(PrintStream) for Java 1.5.0 again. A lesser problem is that when I tried it, it sure threw the exception: [510] cat Roska.java class Roska { public static void main(String [] args) { System.setOut(null); System.out.println("Hello?"); }} [511] javac Roska.java [512] java -cp . Roska Exception in thread "main" java.lang.NullPointerException at Roska.main(Roska.java:3) This is from version 1.4.0; they haven't updated for a while. Maybe you did it in a program that does not use System.out? The exception is not from setOut() but from println() after that. > The main problem I would have with that is that the docs do not say > anything about it - I just looked up System.setOut(PrintStream) for [quoted text clipped - 16 lines] > Maybe you did it in a program that does not use System.out? The > exception is not from setOut() but from println() after that. It's not surprising, you are dereferencing a null. There are three alternatives that come to mind: 1). Don't use System.out, but I guess if that were viable you wouldn't be asking. 2). Redirect stdout to /dev/null outside of the VM: java MyClass > /dev/null 3). Create a sub-class of PrintStream that discards everything and use setOut to point to that. Dan.  SignatureDaniel Dyer http://www.dandyer.co.uk ... >> A lesser problem is that when I tried it, it sure threw the exception: ... >> class Roska { public static void main(String [] args) { >> System.setOut(null); >> System.out.println("Hello?"); >> }} ... > It's not surprising, you are dereferencing a null. It's not just System.out = null; and while the docs say setOut 'reassigns the "standard" output stream', they don't say that it simply reassigns it to its argument as is. > There are three alternatives that come to mind: > > 1). Don't use System.out, but I guess if that were viable you > wouldn't be asking. (The one asking was somebody else. I was just curious about a claim that System.setOut(null) would, maybe, work, so I tried.) > 2). Redirect stdout to /dev/null outside of the VM: > > java MyClass > /dev/null > > 3). Create a sub-class of PrintStream that discards everything and > use setOut to point to that. The winning way so far appears to be to subclass OutputStream so, and pass the resulting OutputStream to the appropriate PrintStream constructor. It's in another branch of this thread already, after I had suggested your number 3. >> There are three alternatives that come to mind: >> [quoted text clipped - 15 lines] > constructor. It's in another branch of this thread already, after I > had suggested your number 3. My apologies, I seem to have missed the other branch of this thread, didn't mean to be redundant. Dan. SignatureDaniel Dyer http://www.dandyer.co.uk >>> is there a garbage file in Java like /dev/null in UNIX? >>> I want temporarily throw away System.out outputs. [quoted text clipped - 21 lines] > Exception in thread "main" java.lang.NullPointerException > at Roska.main(Roska.java:3) I tried it again in 1.6, and it threw the NPE also. I guess I misremembered what I had done. - Oliver Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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