Java: How to configure System.out to have autoflush enabled?

Question

I used reflection like so to print out the properties of the System.out object:

System.out.println("Class: " + System.out.getClass().getName());
for (Field field : ObjectUtils.getAllFields(System.out)) {
    field.setAccessible(true);
    System.out.println("> " + field.getType().getSimpleName() + ' ' + field.getName() + " = " + field.get(System.out));
}

This was the result:

Class: java.io.PrintStream
> boolean autoFlush = false
> boolean trouble = false
> Formatter formatter = null
> BufferedWriter textOut = java.io.BufferedWriter@43c1b556
> OutputStreamWriter charOut = java.io.OutputStreamWriter@587e5365
> boolean closing = false
> OutputStream out = org.apache.tools.ant.util.TeeOutputStream@22fcf7ab

As you can see, the autoflush is set to false. So my question is simple -- how do I configure System.out to have autoflush set to true?

What jvm are you using? I receive autoFlush = true, which is consistent with OpenJDK source code, both for Java 8 and Java 11. For Java11 check: https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/share/classes/java/lang/System.java#L1968 and https://github.com/AdoptOpenJDK/openjdk-jdk11/blob/master/src/java.base/share/classes/java/lang/System.java#L1886 — Lesiak, Jan 29 '20 at 21:26

nylanderDev · Accepted Answer · 2020-01-29T20:41:43.630

5

Wrap it in another stream:

PrintStream newOut = new PrintStream(System.out, true);
// And then set it to out (Credit to David Zimmerman in the comments)
System.setOut(newOut);

edited Jan 29 '20 at 20:41

answered Jan 29 '20 at 20:33

nylanderDev

531
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2

Then System.setOut(newOut) – David Zimmerman Jan 29 '20 at 20:40
1

For more details check the javadoc https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/PrintStream.html#%3Cinit%3E(java.io.OutputStream,boolean) – JuanMoreno Jan 29 '20 at 20:43
1

Or a one-liner: `System.setOut(new PrintStream(System.out, true));` – Dasmowenator Jan 30 '20 at 01:53

score -1 · Answer 2 · edited Jan 29 '20 at 23:10

-1

After System.out.println() execute System.out.flush()

edited Jan 29 '20 at 23:10

JuanMoreno

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answered Jan 29 '20 at 20:34

Sergio Ricardo

17
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1

Not really what **auto**-flush means though. – Zabuzard Jan 30 '20 at 00:00

Java: How to configure System.out to have autoflush enabled?

2 Answers2

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