How do I add a prefix to log4j messages (at the object level)

Question

I use log4j2 and I would like to add a prefix to all my messages. This prefix is passed to the constructor parameter and it depends on the instance of the class. So we're at the object level (not class or thread).

For example, I have an A class instantiated like new A(152), so when I use log.error("message") on this class, 152: is written just before the message. For new A(155), 155: will be displayed instead.

Thanks for your help

Different threads can put different values for the same key. The map is threadlocal so every thread has a separate copy. — Remko Popma, May 24 '13 at 16:20
Finally I created a class LogMessage which implement MessageFactory ans I concatenate message with prefix. After I create logger like this `private Logger logger = LogManager.getLogger("MyClass", new LogMessage(prefix));` and it's work — Lucie, May 29 '13 at 18:20

score 7 · Answer 1 · answered May 23 '13 at 20:18

7

Use MDC to achive this

In your constructor put

 MDC.put("prefix", yourvalue);

and in your XML use it like this in pattern

      %X{prefix}

answered May 23 '13 at 20:18

NullPointerException

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Different threads can put different values for the same key. The map is threadlocal so every thread has a separate copy. – Remko Popma May 24 '13 at 16:19

DairyLea · Answer 2 · 2016-03-11T00:34:47.667

5

Based on Bill Clars answer:

public class LogWrapper
{
    private Logger log;
    private String prefix;

    public LogWrapper(Logger log, String prefix) {
        this.log = log;
        this.prefix = prefix;
    }

    public void error(String msg)
    {
        log.error(prefix + ": " + msg);
    }
}

Then you set as instance variable in your class

public class MyClass {
    private LogWrapper log;

    public MyClass(int prefix) {
        log = new LogWrapper(Logger.getLogger(this.getClass()), String.valueOf(prefix));

        // then log away
        log.error("Test");
    }
}

edited Mar 11 '16 at 00:34

answered May 23 '13 at 20:23

DairyLea

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Or you could extend `Logger` and override the logging methods – DairyLea May 23 '13 at 20:26
1

I tried this before... It will always print the exact same `file:line` as the log message origin. It will always be `LogWrapper:26` because you log4j logger call is at line (e.g.) 26 in your `LogWrapper` class. You'd need to extend the log4j logger, but that's still not trivial (at least, it wasn't on log4j 1.2). – Joanis May 24 '13 at 15:46
As I understood it the question asked to simply prefix a number before all messages... – DairyLea May 24 '13 at 17:50
1

I'm just pointing out that, although answering the question, it's not very practical since you are losing valuable information. Unless you don't care where your logs come from, in which case I'd wonder why you're logging using a logging framework and not simply printing the desired information to a file. – Joanis May 25 '13 at 02:05

jjurm · Answer 3 · 2014-08-25T19:00:56.120

Here is one simple workaround solution: you can wrap the string with a method that adds the prefix to it and returns concatenated string to the error method.

public class A {
    private static final Logger LOG = LogManager.getLogger();

    final int index;

    public A(int index) {
        this.index = index;
    }

    public static void f(String message) {
        return String.valueOf(index) + ": ";
    }

    public void method() {

        // ...

        LOG.error(f("message"));

    }

}

Advantages:

Simple
You can log messages with and also without the prefix in one class/method
You don't have to permanently add something like %X{prefix} to the log4j2 configuration

Disadvantages:

You always have to use the wrapper method if you want to add the prefix

And if you want to use this wrapper method in each class you create, you can use static import instead of declaring the method in each class — jjurm, Aug 25 '14 at 19:02

score 0 · Answer 4 · answered May 23 '13 at 20:13

0

One solution is a wrapper class.

public class YourLogger
{
    private Logger log;

    public void error(int value, String msg)
    {
        log.error(String.valueOf(value) + ": " + msg);
    }
}

answered May 23 '13 at 20:13

Bill Clar

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I try this but the calling class and the line number are lost. – Lucie May 23 '13 at 20:19
@Boubee i thing your variable contain effected code line number.is it ? – KhAn SaAb May 23 '13 at 20:45
No, my variable is a serial number – Lucie May 24 '13 at 13:50
See comment I wrote on DiaryLea's answer. – Joanis May 24 '13 at 15:47

KhAn SaAb · Answer 5 · 2013-05-23T20:31:18.673

0

try this

public void writeError(String msg,int intValue) {
logger.error(intValue+" "+msg);
}

edited May 23 '13 at 20:31

answered May 23 '13 at 20:23

KhAn SaAb

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With this, wouldn't you have to create a method for each logging level, in each class you create? – Joanis May 23 '13 at 20:32
yes i know no need to create seprate methods.for OP 'S understanding i wrote this. – KhAn SaAb May 23 '13 at 20:42

How do I add a prefix to log4j messages (at the object level)

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