How to make System.err write in one block

I'd like to solve following issue: imagine that you are doing lots of outputs in System.out, and from time to time there is an Exception thrown. When you look into the console, you can see that the exception's trace text is mixed up with normal output done by System.out. I understand that these two are开发者_如何学JAVA different streams (System.out and System.err) and I guess that the output of the exception is done internally by some other thread, that is why it is mixed up.

However, is it somehow possible for the code to stop until output for the exception is done? The only solution I can think of is to put Thread.sleep, but maybe there might be some option I am not aware of.

Just curious really :) It'd be nice for debugging (that's the reason I ask, because reading the output and exceptions mixed up in between is terrible)

If you have multiple threads and their output is getting interleaved, you should think about using a logging facility rather than trying to share the stderr and stdout-

http://download.oracle.com/javase/6/docs/api/java/util/logging/package-summary.html

Or apache's log4j:

http://logging.apache.org/log4j/1.2/

How about redirecting System.err to a file?

System.setErr( ... );

The problem needs to be solved elsewhere, in the process which merges two file streams into the output you see - by only printing out a line when it is done. Since that is most likely not an option to you if you are talking about the "java.exe" output, you need to investigate elsewhere.

I have not tested, but I would start with having a look at invoking flush() on System.out before you send output to System.err.

When java implicitly imports the lang (java.lang.*) package, the System class has 2 standard output streams.

System.err System.out

And because these both output to the same standard output, you have to choose one and change it from standard output to file output. My recommendation would be to change the System.err output like so:

import java.io.* ......

System.setErr (new PrintWriter (new FileWriter ("Errors.txt")));

Hope this helps!

EDIT

Sorry, can't leave comments yet, but the logging idea above is very good. Depending on what you are doing, logging will be an optimal solution. But I try to avoid logging because it tends to become very memory extensive if it is used too much.

Write to a separate stream in memory to format your output, then write the single string at once. You may still end up with your single string in the middle of an exception's text, though. Fundamentally what you are doing requires synchronization, or a separate stream (think one output file per thread).

I don't see how Thread.sleep will do anything other than complicate the issue.

Create a new PrintStream to file descriptor 2 with autoflush set to false.

 System.setErr(new PrintStream(new FileOutputStream(FileDescriptor.err, false, "UTF-8")));

Just make sure to call System.err.flush after important error messages.

If you want to merge stderr into stdout, you can do the above but with FileDescriptor.out.