有没有可能在log4j中给堆栈跟踪的每一行都加上前缀？[英] Is it possible to prefix every line of a stacktrace in log4j?

问题描述

when you write

logger.error("message", exception);

log4j produces the message and the complete stack trace :

Aug  9 06:26:13 10.175.60.14 myPrefix: [error] [TP-Processor114] [my.class.Name] message : exception
at fatherOfException
at fatherof_fatherOfException
at fatherof_fatherof_fatherOfException
...

my conversion pattern is

log4j.appender.syslog.layout.ConversionPattern=myPrefix: [%p] [%t] [%c] [%x] - %m%n

So, is it possible to prefix every line with myPrefix, as :

    Aug  9 06:26:13 10.175.60.14 myPrefix: [error] [TP-Processor114] [my.class.Name] message : exception
myPrefix    at fatherOfException
myPrefix    at fatherof_fatherOfException
myPrefix    at fatherof_fatherof_fatherOfException
    ...

When I grep my logs on myPrefix, i don't see the stack trace. We have many different prefixes (one per module)

Thanks in advance.

推荐答案

Subclass ThrowableRenderer, for example:

import org.apache.log4j.DefaultThrowableRenderer;
import org.apache.log4j.spi.ThrowableRenderer;

public class LogThrowableRenderer implements ThrowableRenderer {

    DefaultThrowableRenderer def = new DefaultThrowableRenderer();

    @Override
    public String[] doRender(Throwable t) {
        String[] temp = def.doRender(t);
        for (int i = 0; i < temp.length; i++) {
            temp[i] = "myPrefix "+temp[i];
        }
        return temp;
    }

}

Add to your log4j.properties:

log4j.throwableRenderer=whatever.package.LogThrowableRenderer

This uses the existing DefaultThrowableRenderer to render the stacktrace in the familiar way before adding the prefix, so it will include the Throwable class, message, and cause.

其他推荐答案

Refer to Alex's answer as it's a cleaner one.

You can write your own implementation of org.apache.log4j.spi.ThrowableRenderer:

http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/spi/ThrowableRenderer.html

Then, edit your log4j configuration:

log4j.throwableRenderer=your-custom-class-name

The ThrowableRenderer returns an array of Strings. Here's your code:

String prefix = "myPrefix"; // Or some constant

List<String> l = new LinkedList<String>();
l.add(String.format("%s %s: %s", prefix, t.getClass().getName(), t.getMessage()));

for (StackTraceElement ste: t.getStackTrace()){
    l.add(String.format("%s %s", prefix, ste.toString()));
}

return (String[]) l.toArray();

Another idea would be to print the Throwable into a PrintWriter that is wrapping some Writer that writes into memory, and then re-iterate over strings delimited by line.separator, adding each line to a list:

StringWriter sw = new StringWriter();
t.printStackTrace(new PrintWriter(sw));

List<String> l = new LinkedList<String>();
for (String s: sw.toString().split(System.lineSeparator())) {
    l.add(String.format("%s %s", prefix, s));
}

return (String[]) l.toArray();

其他推荐答案

With log4j2 you can add a prefix to each new line of your stacktraces by specifying the separator as a newline followed by your prefix:

%xThrowable{separator(\nmyPrefix)}%n

You can similarly add prefixes to each new line of each multi-line message:

%replace{%m}{[\r\n]+}{\nmyPrefix}

For example, to add a whitespace prefix to each multi-line log and stacktrace line:

appender.rolling.layout.pattern = %d [%t] %-5p %c %L - %replace{%m}{[\r\n]+}{\n }%xThrowable{separator(\n )}%n

Note that you want place the %xThrowable bit after your %m.