Setting log level of message at runtime in slf4j

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When using log4j, the Logger.log(Priority p, Object message) method is available and can be used to log a message at a log level determined at runtime. We're using this fact and this tip to redirect stderr to a logger at a specific log level.

slf4j doesn't have a generic log() method that I can find. Does that mean there's no way to implement the above?

There is no way to do this with slf4j.

I imagine that the reason that this functionality is missing is that it is next to impossible to construct a Level type for slf4j that can be efficiently mapped to the Level (or equivalent) type used in all of the possible logging implementations behind the facade. Alternatively, the designers decided that your use-case is too unusual to justify the overheads of supporting it.

Concerning @ripper234's use-case (unit testing), I think the pragmatic solution is modify the unit test(s) to hard-wire knowledge of what logging system is behind the slf4j facade ... when running the unit tests.

change log level at runtime (logback and slf4j) � GitHub, We want to try to write concise informative messages that are self-explanatory and able to be dumped soon after, as needed. Here are some of� Setting log level of message at runtime in slf4j (8) . Anyone wanting a drop-in fully SLF4J compatible solution to this problem might want to check out Lidalia SLF4J Extensions - it's on Maven Central.

Richard Fearn has the right idea, so I wrote up the full class based on his skeleton code. It's hopefully short enough to post here. Copy & paste for enjoyment. I should probably add some magic incantation, too: "This code is released to the public domain"

import org.slf4j.Logger;

public class LogLevel {

    /**
     * Allowed levels, as an enum. Import using "import [package].LogLevel.Level"
     * Every logging implementation has something like this except SLF4J.
     */

    public static enum Level {
        TRACE, DEBUG, INFO, WARN, ERROR
    }

    /**
     * This class cannot be instantiated, why would you want to?
     */

    private LogLevel() {
        // Unreachable
    }

    /**
     * Log at the specified level. If the "logger" is null, nothing is logged.
     * If the "level" is null, nothing is logged. If the "txt" is null,
     * behaviour depends on the SLF4J implementation.
     */

    public static void log(Logger logger, Level level, String txt) {
        if (logger != null && level != null) {
            switch (level) {
            case TRACE:
                logger.trace(txt);
                break;
            case DEBUG:
                logger.debug(txt);
                break;
            case INFO:
                logger.info(txt);
                break;
            case WARN:
                logger.warn(txt);
                break;
            case ERROR:
                logger.error(txt);
                break;
            }
        }
    }

    /**
     * Log at the specified level. If the "logger" is null, nothing is logged.
     * If the "level" is null, nothing is logged. If the "format" or the "argArray"
     * are null, behaviour depends on the SLF4J-backing implementation.
     */

    public static void log(Logger logger, Level level, String format, Object[] argArray) {
        if (logger != null && level != null) {
            switch (level) {
            case TRACE:
                logger.trace(format, argArray);
                break;
            case DEBUG:
                logger.debug(format, argArray);
                break;
            case INFO:
                logger.info(format, argArray);
                break;
            case WARN:
                logger.warn(format, argArray);
                break;
            case ERROR:
                logger.error(format, argArray);
                break;
            }
        }
    }

    /**
     * Log at the specified level, with a Throwable on top. If the "logger" is null,
     * nothing is logged. If the "level" is null, nothing is logged. If the "format" or
     * the "argArray" or the "throwable" are null, behaviour depends on the SLF4J-backing
     * implementation.
     */

    public static void log(Logger logger, Level level, String txt, Throwable throwable) {
        if (logger != null && level != null) {
            switch (level) {
            case TRACE:
                logger.trace(txt, throwable);
                break;
            case DEBUG:
                logger.debug(txt, throwable);
                break;
            case INFO:
                logger.info(txt, throwable);
                break;
            case WARN:
                logger.warn(txt, throwable);
                break;
            case ERROR:
                logger.error(txt, throwable);
                break;
            }
        }
    }

    /**
     * Check whether a SLF4J logger is enabled for a certain loglevel. 
     * If the "logger" or the "level" is null, false is returned.
     */

    public static boolean isEnabledFor(Logger logger, Level level) {
        boolean res = false;
        if (logger != null && level != null) {
            switch (level) {
            case TRACE:
                res = logger.isTraceEnabled();
                break;
            case DEBUG:
                res = logger.isDebugEnabled();
                break;
            case INFO:
                res = logger.isInfoEnabled();
                break;
            case WARN:
                res = logger.isWarnEnabled();
                break;
            case ERROR:
                res = logger.isErrorEnabled();
                break;
            }
        }
        return res;
    }
}

How to dynamically change log level in SLF4j Log4J with , Most applications set the logger level to INFO in the production environment, but sometimes we need more detailed logging messages to� I understand the it's currently impossible to configure SLF4J's log level's at runtime. I don't fully understand the reasons for this. This is the first thing that I tried to do with SLF4J 10 minutes after integrating it - I would like to reduce the clutter I'm getting when running unit tests, and I would prefer to do this via code and not

Try switching to Logback and use

ch.qos.logback.classic.Logger rootLogger = (ch.qos.logback.classic.Logger)LoggerFactory.getLogger(ch.qos.logback.classic.Logger.ROOT_LOGGER_NAME);
rootLogger.setLevel(Level.toLevel("info"));

I believe this will be the only call to Logback and the rest of your code will remain unchanged. Logback uses SLF4J and the migration will be painless, just the xml config files will have to be changed.

Remember to set the log level back after you're done.

Logback Change Log Level at Runtime Example, Then check out our detailed example on SLF4J Logging Levels! We have defined logback as the runtime dependency. SSS} [%thread] %-5level %logger {36} %msg%n and encoder is set to PatternLayoutEncoder by� log4j provides you configuration file based level setting which sets you free from changing the source code when you want to change the debugging level. Following is an example configuration file which would perform the same task as we did using the log.setLevel(Level.WARN) method in the above example.

You can implement this using Java 8 lambdas.

import java.util.HashMap;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.event.Level;

public class LevelLogger {
    private static final Logger LOGGER = LoggerFactory.getLogger(LevelLogger.class);
    private static final Map<Level, LoggingFunction> map;

    static {
        map = new HashMap<>();
        map.put(Level.TRACE, (o) -> LOGGER.trace(o));
        map.put(Level.DEBUG, (o) -> LOGGER.debug(o));
        map.put(Level.INFO, (o) -> LOGGER.info(o));
        map.put(Level.WARN, (o) -> LOGGER.warn(o));
        map.put(Level.ERROR, (o) -> LOGGER.error(o));
    }

    public static void log(Level level, String s) {
        map.get(level).log(s);
    }

    @FunctionalInterface
    private interface LoggingFunction {
        public void log(String arg);
    }
}

SLF4J Logging Levels Example, incurs the cost of constructing the message parameter, On the other hand, if the logger is enabled for the DEBUG level, you will incur the which will print as "Set {1,2} differs from 3". For setting level on your own package use different file per logging implementation. Setting log level of message at runtime in slf4j. 1350. String formatting

This can be done with an enum and a helper method:

enum LogLevel {
    TRACE,
    DEBUG,
    INFO,
    WARN,
    ERROR,
}

public static void log(Logger logger, LogLevel level, String format, Object[] argArray) {
    switch (level) {
        case TRACE:
            logger.trace(format, argArray);
            break;
        case DEBUG:
            logger.debug(format, argArray);
            break;
        case INFO:
            logger.info(format, argArray);
            break;
        case WARN:
            logger.warn(format, argArray);
            break;
        case ERROR:
            logger.error(format, argArray);
            break;
    }
}

// example usage:
private static final Logger logger = ...
final LogLevel level = ...
log(logger, level, "Something bad happened", ...);

You could add other variants of log, say if you wanted generic equivalents of SLF4J's 1-parameter or 2-parameter warn/error/etc. methods.

SLF4J FAQ, Explore different ways of controlling the logging level at runtime in a Spring Boot Application. log.trace("This is a TRACE level message"); By default, our Spring Boot applications are using the Logback logging library. Slf4j and Log4j Binding. Changing LogLevel Dynamically. We do not have a way to change log level from slf4j api and we need to rely on implementation, in our case log4j api. First get rootLogger with log4j then set the level on it. Here is an example code for the same

Changing the Logging Level at the Runtime for a Spring Boot , util.logging. So If you want to change the log level, the best way to do this is via the configuration of your logging implementation: See� If unspecified, the level of nearest parent logger will be used, and if none is set, then the value specified by org.slf4j.simpleLogger.defaultLogLevel will be used. org.slf4j.simpleLogger.showDateTime - Set to true if you want the current date and time to be included in output messages.

Update slf4j Log Level Programmatically – web/code, In your runtime, you also need a SLF4J backend. If you set the loglevel to a higher level than DEBUG , any DEBUG while the underlying infrastructure writes the log messages to disk or other configured destination. You mentioned the slf4j-jdk14-1.6.1.jar. This provides the slf4j binding to java.util.logging. You need to have that in your classpath, but make sure you also have the slf4j api (slf4j-api-1.7.12.jar) in your classpath as well.

Classic Logging • Akka Documentation, DataStax Java driver uses the popular SLF4J library to emit log messages; SLF4J has set up their classpath and runtime configuration to be able to capture log messages You need to set the above loggers to DEBUG level to turn them on. An SLF4J binding designates an artifact such as slf4j-jdk14.jar or slf4j-log4j12.jar used to bind slf4j to an underlying logging framework, say, java.util.logging and respectively log4j. From the client's perspective all versions of slf4j-api are compatible.

Comments
  • It looks like there's some discussion of adding this to slf4j 2.0 on the dev mailing list: qos.ch/pipermail/slf4j-dev/2010-March/002865.html
  • take a look at Marker, this is custom data you can pass to log chain.
  • @tuxSlayer can you please elaborate how to use Marker in this case?
  • Probably its not the best idea for "logging" but you can use several markers for log entry "priority" (high|low|normal, info|warn|fatal) and use filtering in logback or custom appender to consume markers and drive log entries into separate channels (log info, email fatal etc). However, the more straight way is to have a facade for this as was pointed in answers below.
  • This feature is supposed to be part of slf4j 2.0. jira.qos.ch/browse/SLF4J-124 See my answer for details and for a possible slf4j 1.x-workaround.
  • There's no mapping necessary really. There are five levels already implicitly defined by the methods in org.slf4j.Logger: debug, error, info, trace, warn.
  • And the issues got closed as Invalid. As far as I understand this, it is a deliberate design choice.
  • @ripper234 - I don't think your bug addressed the same issue as scompt.com's original question. You asked about configuring the level of the underlying logging system via the SLF4J API. What scompt.com was after was a generic 'log' method in the SLF4J API, that takes the logging level of the message as a parameter.
  • +1 @RichardFearn And one cannot undo the comment upvote after 60 seconds, meh. Feature request is existing meanwhile: bugzilla.slf4j.org/show_bug.cgi?id=133
  • The RFE links don't resolve any more. The relevant links are now: jira.qos.ch/browse/SLF4J-124 and jira.qos.ch/browse/SLF4J-197 ... and both have been closed. Read the comments for the rationale.
  • This would be easier to use with a variadic (Object...) args parameter.