System.err

what is the perpose of 'err' reference variable in System class. and how to use it?

System.out leads the output to the standard output stream (normally mapped to the console screen). System.err leads the output to the standard error stream (and, by default to the console, as well). The idea behind having these two is that the standard output should be used for regular program output, and standard error should be used for error messages.
Both the streams can be redirected to different destinations. If it is desired to redirect the output to an output file and error messages to a different log file, than on UNIX it can be done as follows:
java MyClass > output.log 2>error.log
This causes the regular output (using System.out) to be stored in output.log and error messages (using System.err) to be stored in error.log.
If you have put error messages in your program, but you don�t want to see them, the technique given below can be used to do it:
Java MyClass 2> /null
This redirects the System.err messages to /null, so no error messages appear on the screen, but the normal program output can still be seen.
Once again, google is your friend!!
regards,
Manuel Leiria

Similar Messages

[Feature Request] Seperate tab in log window for System.err

By default, the stack traces of exceptions (and throwables in general) are printed to the System.err stream. So, wouldn't it be useful to include a 2nd tab for System.err messages?
It could be optional to either include or leave out the System.err output in the System.out tab.
The whole idea of this 2nd tab is to set it up like the search output tab: a tree-like list which can be expanded to see the stack trace of each exception that occured during runtime. A small parser can parse the stack trace when an exception is printed on the System.err stream and format it.
If this option would be availble in the debugger only, that would be ok too, I guess. Although, the debugger already has some other means of jumping through code when an exception is thrown (ie, when the debugger 'pauses' runtime).

I've logged an Enhancement request to improve the handling of System.err messages (2811508). There are ways to enhance the treatment of System.err messages without introducing a new tab, through the use of color, links back to the source code, and collapsing of entire stack traces to a single line (with a button to see the entire trace).
Thanks!
-- Brian

How to capture System.err and System.out in a method?

Is there some way to capture everything that is sent to System.err or System.out and have it instead go to e.g. a method as a String?
The reason I want to do is this: I am invoking some method from a class that sends output to System.err and System.out but while that method is run, I want everything that goes to System.out or System.err to instead go to a String buffer or a Swing Scroll Pane.
What is the easiest way to do this?

I want everything that goes to System.out or System.err to instead go to a String buffer or a Swing Scroll Pane.Then maybe you should be searching (and then posting) in the Swing forum. Thats where I've seen this question asked and answered many times in the past.

Passing System.out/System.err as parameters

I'm sure there must be a simple answer to this that I'm just not seeing, suggestions please.
I have a method in a logging utility that takes either a PrintWriter or a Printstream parameter as a target for logging and a second method that closes the log.
In principle either System.out or System.err could be passed in either directly or wrapped in a PrintWriter.
In the closing method I want to determine if one of these two PrintStreams were passed and if so skip the close() operation so as not to lose connectivity to stdout or stderr.
In the case of the PrintStream parameter I can use an identity check and condition a boolean to control closing the file.
The problem is the PrintWriter, if the utility user wraps these PrintStreams.
1: As I understand it closing the PrintWriter will cause the underlying OutputStream to close.
2: Since it's a protected field the underlying OutputStream is not visible to me.
3: I don't wish to subclass PrintWriter if there's another way to solve the problem.
Any ideas?

Why don't you use a BufferedWriter() ?

Redirecting System.err on a mobile phone?

Hi,
Is there a way of redirecting System.err? Unfortunately, System.setErr does not exist in MIDP, so I haven't been able to write my own PrintStream to replace err.
I need to know what the output of Exception.printStackTrace() is at a certain point. There is certainly a way of accessing System.err, otherwise it wouldn't be present in MIDP ... .
Thanks!
Stefan

Hi
J2ME Polish provides a logging framework, which offers different logging levels and the ability to view logging messages on real devices.
Mihai

System.out and System.err

Hi all,
This is a stupid newbie question, but I could not find the answer on the Web
site, so here goes: Where do System.out and System.err get written to? I'm
trying to deploy some plain-vanilla stateless session beans that do a bunch
of println() calls, but I can't see the output anywhere! The WebLogic
Console shows no messages, /myserver/weblogic.log has nothing interesting,
and there are no .log files anywhere that I can see. I even searched /tmp
and found nothing of interest. What am I missing? Do I have to explicitly
open a file for System.out and/or System.err? That doesn't sound right...
- danz

The simple answer to your questions are no and no.
I recently logged a problem with BEA WebLogic technical support regarding
this issue and their response is:
You have two choices. You can either use standard Java file i/o to write
your output to a file, or you can use our t3loggingservices to append
messages into the weblogic.log
The "jump point" for the logging services is at --
http://www.weblogic.com/docs51/classdocs/javadocs/weblogic/common/LogService
sDef.html
It is actually very easy to use -- after you import the proper packages into
your web application it is just as easy to use as System.out.println.
John J. Feigal Voice (651)766-8787 (main)
Sr. Technical Consultant (651)766-7249 (direct)
Ensodex, Inc. Fax (651)766-8792
4105 N. Lexington Ave., Suite 150 email [email protected]
Arden Hills, MN 55126 WebSite http://www.ensodex.com
"Jon Wynett" <[email protected]> wrote in message
news:[email protected]...
I'm running WebLogic as an NT Service. Is there any way to see the
System.out.println messages? Can they be redirected to the weblogic.log
file?
We were running through a DOS Window and saw all the messages, however we
ideally want to run Weblogic as a service.
"Rob Woollen" <[email protected]> wrote in message
news:[email protected]...
I'm guessing that you started the server with the .exe file on Windows.
If you're debugging with printlns, it's generally more conventient to
use the startWebLogic.sh or startWebLogic.cmd files to start the server
from a shell.
By default, you'll see stdout and stderr in the window.
-- Rob
Dan Zivkovic wrote:
Hi all,
This is a stupid newbie question, but I could not find the answer on
the
Web
site, so here goes: Where do System.out and System.err get written to?I'm
trying to deploy some plain-vanilla stateless session beans that do abunch
of println() calls, but I can't see the output anywhere! The WebLogic
Console shows no messages, /myserver/weblogic.log has nothinginteresting,
and there are no .log files anywhere that I can see. I even searched/tmp
and found nothing of interest. What am I missing? Do I have toexplicitly
open a file for System.out and/or System.err? That doesn't soundright...
- danz

Using System.err.println() from within the classes of WAS ?

hi,
I am using admin.jar,a jar file which is being used by Web Application Server in my own class.
I am referencing some of the classes from admin.jar from my class.
I tried to print some trace statements,using System.err.println() from within the classes in admin.jar but they did not reflect in defaulttrace0.trc.
I made these changes in the admin.jar being used by WAS.
I restarted the server and even restarted the machine but without success.
I want to know how to print System.out.println() statements from within the classes in admin.jar.
Also, am i looking for these statements in the right file for eg. defaulttrace0.trc. or is it some other file that i need to look into.
I need urgent help on this.
Reward points assured.
thanks a lot.
Saurav

thanks craig,
ur answer has helped me a lot.but it didnt quite help me.
nevertheless i am trying to set different levels of severity.
Is there anything else that i can do.
Also,i commented out a line of code today in one of the class DataSourceManagerImpl.java in sapj2eenginedeploy.jar
for eg. temp.delete in it deploy method.Buth that line still executed.
I m totally lost as to wht to do.
I m trying to create a datasource from my application in WAS.For that i m using the WAS APIs.But its not working completely.
I am using the above jar and its method createdatasource.
I am callin it from my application's class.
It creates a datasource and i can see it in JDBC Connector list in Visual Administrator.But it appears with red sign meaning its not started.When i start it from the tool then it starts.
But in defaulttrace.trc file it shows an error "FileNotFindException". This happens,and i am very much sure, in the deploy() of DataSourceManagerImpl.java class of sapj2eenginedeploy.jar.
i want to apply println inside this method so i may know where exactly i ma getting the error and get so more info so i may solve my problem.
pls help me.
its really urgent.
thanks again
saurav

One JVM with different system.out / system.err files

I have a menu application which allows me to launch different swingapps which runs inside one single JVM.
All applications have their own properties.file which is read and handled at the start of each application.
One property allows me to print all kind of system.err / system.out which i want to redirect to a specific file. This is implemented with following code:
        if (isTRACE_ENABLED()){
            try {
                setTrace_out_log(new PrintStream(
                          new BufferedOutputStream(
                                new FileOutputStream(props.getProperty("TRACE_OUTLOG_FILE")),128), true));
                System.setOut(getTrace_out_log());
                setTrace_err_log(new PrintStream(
                        new BufferedOutputStream(
                              new FileOutputStream(props.getProperty("TRACE_ERRLOG_FILE")),128), true));
                System.setErr(getTrace_err_log());
            } catch(IOException e) {
                e.printStackTrace();
        }This works file but... all system.out and system.err is redirected to same file... which is not what i want.
Example:
debug property for menu application = enabled
debug property for app 1 = disabled
debug property for app 2 = enabled
In above case i want to have 4 new files:
- menuapp_out
- menuapp_err
- app2_out
- app2_err
This doesn't work, the files are created but after starting app2, the print-statements for the menu application are alse redirected to the app_2_xxx files. And when i finish app2, i do not get any print-output anymore
IMHO this is because the JVM only has 1 system.out and 1 system.err file. Is there some way to solve this?

I understand that i need to use java.util.logger (JUL) or Log4j
Are there any (free) tools availabe to read/analyze the logfiles created by above tools?

Redirecting System.err to a JOptionPane

Hello,
I tried to write a piece of code which shows all exceptions in a JOptionPane instead of the console. But I meet two difficulties:
1. I don't know how to detect the line count of the error message (so that currently I have to display the optionPane for each error line, which is unacceptable).
2. I receive more error messages than expected. The produced parse error gives 5 lines on a console, but here I receive 60.
What's wrong?
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
class Redirecting extends JFrame {
public Redirecting() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(300,300);
    JTextAreaOutputStream err= new JTextAreaOutputStream();
    System.setErr(new PrintStream(err));
    JButton b= new JButton("Produce error");
    b.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
     System.out.println(Integer.parseInt("1"));
     System.out.println(Integer.parseInt("2"));
     System.out.println(Integer.parseInt("Error"));
    add(b, BorderLayout.SOUTH);
    setVisible(true);
public static void main(String[] args) throws Exception {
    EventQueue.invokeLater(new Runnable() {
      public void run() {
     new Redirecting();
class JTextAreaOutputStream extends OutputStream {
    int icnt=0;
    private JTextArea area;
    public JTextAreaOutputStream() {
      area= new JTextArea();
    public void flush() throws IOException {
      JOptionPane.showMessageDialog(Redirecting.this, area, "Error",
                              JOptionPane.ERROR_MESSAGE);
//      area.setText("");
    public void write(byte b[]) throws IOException {
      area.append(new String(b));
    public void write(byte b[], int off, int len) throws IOException {
      System.out.println(icnt++);
      String s = new String(b , off , len);
      area.append(s);
      flush(); // to make error lines visible
    public void write(int b) throws IOException {
      area.append(String.valueOf(b));
}

maybe this ?
      * recieving error for testing
      * @param e
     protected void bt_generateError_actionPerformed(ActionEvent e) {
          DateFormat fo = new SimpleDateFormat("mm.dd.yyyy");
          try {
               // Here reciev parsing error
               fo.parse("sacascsa");
          } catch (ParseException e1) {
               String exception = Util.formateException(e1.getStackTrace());
               // show error
               Util.showException(frame, exception);
      * utilita
      * @author Dima
     public static class Util {
           * formateException formating error in way you want
           * @param stack
           * @return
          public static String formateException(StackTraceElement[] stack) {
               String formatedException = "";
               for (int i = 0; i < stack.length; i++) {
                    System.err.println(stack.getClassName() + ""
                              + stack[i].getMethodName() + "" + stack[i].getClass()
                              + " Line" + stack[i].getLineNumber());
                    formatedException = formatedException.concat(
                              stack[i].getClassName()
                              + "."
                              + stack[i].getMethodName()
                              + " "
                              + stack[i].getClass()
                              /** + " Line" + stack[i].getLineNumber() */
                              + "\n"); // remove comment and recieve errors line
                                             // numbers
               return formatedException;
          * showException return JOptionPane with formatted error
          * @param com
          * @param exceptionText
          public static void showException(Component com, String exceptionText) {
               JPanel canva = new JPanel();
               canva.setMinimumSize(new Dimension(300, 200));
               canva.setPreferredSize(new Dimension(300, 200));
               JTextArea area = new JTextArea();
               area.setText(exceptionText);
               JScrollPane pan = new JScrollPane();
               pan.getViewport().setView(area);
               canva.setLayout(new BorderLayout());
               canva.add(pan);
               JOptionPane.showMessageDialog(com, canva, "Error Title",
                         JOptionPane.ERROR_MESSAGE);

Redirecting System.err to a TextArea

Hi there !
I want to redirect the output of System.err to a TextArea.
System.err is everywhere in my project. Is there any simple way to just redirect the output of this err to some TextArea?
Thanks in Advance
Dexter

See the API java.lang.System.setErr()You will then need to start a thread to read from the PrintStream and put the
output in your text area.
- ajay

How do I redirect System.err output in iPlanet 4.1?

All,
I've been trying for days to redirect System.err output from a Java program
to a log file. I followed the instructions here:
http://knowledgebase.iplanet.com/ikb/kb/articles/4790.html
Unfortunately, nothing has been written to any of the log files (even though
I have plenty of System.err.println()'s in my code).
Anyone else get this to work correctly?
Thanks in advance,
--Bill

Hi,
What is the product web server or application server ? If it is application
server then I'm very sure that this output will be seen in the kjs log file in
Unix and in the command window in Windows NT/2K, only if you have allowed the
process to interact with desktop. Please let me know if this answers your
question for me to help you further on this.
Regards
Raj
"news.uswest.net" wrote:
All,
I've been trying for days to redirect System.err output from a Java program
to a log file. I followed the instructions here:
http://knowledgebase.iplanet.com/ikb/kb/articles/4790.html
Unfortunately, nothing has been written to any of the log files (even though
I have plenty of System.err.println()'s in my code).
Anyone else get this to work correctly?
Thanks in advance,
--Bill

System.out and System.err How to get to show up in log

Does anyone know if there is anyway to get System.out and System.err
messages to appear in the log?
Trying to build and debug a JSP project is a complete nightmare when the
remote developers cannot see System.out or System.err messages from helper
classes.
Platform= Windows NT 4.0
Weblogic running as a Service
Thanks in advance!

Write a wrapper class to redirect the std out to what ever stream you want.
HTH
Saman

System.out and System.err to files

Hi !
Could somebody tell me, how I can forward all System.out.println and System.err.println Messages from
my Java modules (EJB, Servlets) to different files respectively.
Thanks
Steve

I think you could create PrinStreamS from your desired output files and then use System.setOut(<...>) and System.setErr(<...>). Place this code in a servlet that you load at startup...

System.out vs. System.err -- best practices?

When I catch an exception, where is the best place to write the stack trace, etc? Should I write it to System.out or System.err?
Thanks,
Curt

If you call printStackTrace() it will by default print to the to the standard error stream.
But really you should look at log4j.

System.out vs System.err questions

Hello,
System.out and System.err both seem to direct regular and error output to the stdout. I have the following questions:
1. I used System.setOut() to direct regular output to "Output.txt" and System.setErr() to direct errors to "Errors.txt". I purposely made the program to throw some exceptions, wanting to redirect them to "Errors.txt". It did not work. My question is "What kind of errors setErr() would direct to an error file?"
2. Without using setErr(), errors go to stdout. My question is "Does Java hava a configuration file I can configue to direct regular output to stdout, but errors to a user-defined file such as errors.log?"
Thanks!

I see the stack trace in file err.txt:
import java.io.*;
public class Example {
    public static void main(String[] args) throws FileNotFoundException {
        System.setOut(new PrintStream(new FileOutputStream("out.txt"), true));
        System.setErr(new PrintStream(new FileOutputStream("err.txt"), true));
        System.out.println("<stdout>");
        System.err.println("<stderr>");
        throw new RuntimeException("here we go");
}

System.our and System.err

Hi,
Is there a buffer size for system.out and System.err.
If so how can we retrieve the buffer size.
Thanking You,
Chamal.

There is no way to determine the characteristics of the OutputStream behind System.out or System.err.
You could provide your own streams (via setOut() and/or setErr() methods)...
Why do you need to know?

System.err

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